Rain & Snow Will Develop Today ( Jan 17 ) With Amounts Varying From Little To None Up to 1-3″

I have expanded my accumulations to now include more of the area, with snow accumulating at temperatures above freezing northward to Clintwood.

A fast moving weather system will spread a mix of rain and snow across the mountain area Thursday, with cooling on upslope winds expected to favor locations along and south of the High Knob Massif for greatest snowfall amounts.

A Major Weather Change Is Expected This Weekend With Strong Winds & Rain Saturday Giving Way To Plunging Temperatures & Wind Chills Sunday

Temperature are expected to fall through the 10s at lower-middle elevations, and through the single digits at upper elevations, during Sunday, with colder wind chills.

Former Alerts Ending Late Evening_January 16

ALERT For Low Cloud Bases On Northerly Upslope Flow With Dense Fog Changing To Freezing Fog At Middle-Upper Elevations Along & Northwest-North  Of The High Knob Massif-Tennessee Valley Divide.

Drizzle to freezing drizzle & light snow will also be possible. Any snow accumulations are expected to be light.  

Caution Is Advised For Low Visibility & Icing On Above Ground Objects.  Icy Patches On Roadways, Especially Secondary Routes At Higher Elevations, Will Be Possible.  Dense Fog Will Be Most Consistent And Widespread Above 2500-3000 Feet.

Rime deposition with freezing fog ( clouds ) began at the summit level of the High Knob Massif around 8:00 PM on January 13.  

Freezing levels had dropped downward to higher portions of the Wise Plateau at 11:00 PM on Sunday, and will continue dropping into Monday AM.

Temperatures will remain below freezing at upper elevations through a prolonged period and will also struggle to rise above low-mid 30s, beneath an 875 MB centered inversion, to maintain raw, cold and damp conditions at middle to lower elevations.

Update – Monday Afternoon_January 14, 2019

My alert will continue tonight as freezing fog has become widespread at elevations above 2500 feet, locally dropping to around 2000 feet, in locations on upslope flow along and north of the High Knob Massif and Tennessee Valley Divide.  Be safe and slow down.

Weather Headlines ( January 14-21 )

A short break, with partial mixing out of an inversion centered around 875 MB, on Tuesday PM gave way to more low clouds and renewed riming at the upper elevations where amounts were already significant.

So I left my alert for fog and low clouds through the daylight hours of Wednesday ( riming continues at highest elevations as of 1 AM Thursday ). 

Following another nasty system today ( Jan 17 ) focus will shift to a major event this weekend which will bring the first of what likely will be numerous blasts of arctic air into the Appalachians.

Previous Headlines

Nasty conditions brought by a Miller B style winter storm during the weekend will finally improve on Tuesday as sunshine returns.

Conditions will begin to deteriorate later this week with strong winds and rain developing well in advance of a major arctic outbreak.

Rising heights with building High pressure at high latitudes and lowering heights at middle latitudes will begin driving bitterly cold, arctic air southward later this week into the January 20-21 weekend.

Although specific details remain to be worked out from this distance, and changes are certain to occur from current projections, a threat for severe winter conditions is great enough to begin highlighting it now ( given this could be life threatening for those caught unprepared for such conditions ).

Given a major Sudden Stratospheric Warming that already has occurred, this increases the odds for a major intrusion of bitterly cold air.  This has now been on the table for weeks, so it should not be a surprise that middle latitude weather is poised to turn severe.  In fact, timing is nearly ideal, based upon past climatology for such events.

This major mid-winter warming event ( SSW or Sudden Stratospheric Warming ) at high altitudes above the arctic became official at beginning of the new year on January 1.

This resulted in a splitting of the Polar Vortex, with two major centers currently dominating the 10 MB flow field within the stratosphere.

10 MB Flow Field_Stratosphere

Although temperatures are cooling again in the arctic stratosphere, winds continue to be reversed and are predicted to remain easterly through the next 10 days as the impacts of this major SSW are working downward into the troposphere.

Major teleconnections on both the European and GFS ensembles are trending in the direction conducive for severe winter conditions in the eastern USA.

-AO ( Arctic Oscillation )
-NAO ( North Atlantic Oscillation )
+/-PNA ( Pacific-NA Oscillation )
-EPO ( Eastern Pacific Oscillation )
-WPO ( Western Pacific Oscillation )

A +ENSO ( Modoki type ) is currently running.

A small negative trend in the PNA being offset by a much larger negative trend in the EPO.  A point of notable inflection in these indices, centered on the January 20-21 weekend, is often indicative of major cyclogenesis; otherwise, the longer-term tendency being toward bad-severe winter conditions with or without major cyclogenesis by this weekend.

Since I consider this upcoming pattern to be so important, I have inserted a preliminary look at my weekly weather column, to be officially published on January 16, for those interested in a more plainly worded description of what is expected ( * ).

It should be stressed that the most important aspect that I am trying to get across is not whether a major arctic blast hits exactly on January 20-21, but rather that a hemispheric pattern change forced by changes already observed in the stratosphere will be setting the stage for severe winter conditions during weeks encompassing the second half of winter and possibly into Spring 2019.

*This marks 26 years that I have written weather columns.

January 1985 Arctic Outbreak

The core of this upcoming air mass will have temps at or below -25 degrees Celsius.  Many factors yet to be determined will dictate if that type of air mass can reach the Mountain Empire, with snow cover, both locally and to our north, being critical to how cold temperatures ultimately get in the short-term.

A major winter storm, likely with more than one wave, will be impacting the eastern USA within the baroclinic zone ( temp contrast ) that forms and intensifies ahead of incoming bitter air.

Stay tuned for later updates and details.

Mountain Area Weather Alerts

While Rain Is Expected To Dominate Saturday Night Into Sunday In Most Locations, Prior To A Change To Light Snow, Freezing Rain Remains A Possibility At Upper Elevations Within The High Knob Massif.

Update_10:30 PM Saturday

A major ice storm in mid-November 2018 caused extensive tree damage at highest elevations in the High Knob Massif, blocking roads and severely damaging some trees.  

While I do not expect this event to be nearly that severe, it only takes a little bit of ice to cause trouble.

Caution is advised for travelers into high elevations  of the High Knob Massif where icing has occurred this evening ( January 12 ) at upper elevations, mainly at elevations above 3300 feet, along State Route 619 and adjoining roadways.

A complicated, messy winter storm of the Miller B type is expected to begin impacting mountain area conditions by early Saturday ( January 12 ).

Cold air in place will initially support all snow before a layer of above freezing air aloft moves over the Tennessee Valley and southern Appalachians to force a change in precipitation type to a cold, nasty rain for most ( freezing rain remaining possible at upper elevations within the  High Knob Massif ).

Cloud bases will drop and precipitation will change back to snow by later Sunday into Monday morning with a rather prolonged period of freezing fog ( riming ) possible at the upper elevations along and north of the High Knob Massif-Tennessee Valley Divide ( mid-elevations above 2500 feet could also be impacted ).

Cloud Bases Are Expected To Lower On Northerly Upslope Flow With Dense Fog Changing To Freezing Fog And Becoming Widespread At Upper Elevations Sunday Into Monday.  Snow amounts will be light.

Former Alerts

A Period Of Snow Will Develop During The Predawn-Morning Hours Of Saturday Before A Break Develops In Advance Of Another Wave Of Moisture With Mixed Precipitation By Later Saturday.  Due To The Current Arctic Air Mass Hazardous Road Conditions Will Be Likely Early Saturday.  Caution Is Advised.

 

Mountain Area Forecast ( Jan 11-14 )

Friday Night Into Saturday Morning

Becoming cloudy with snow developing from high to low elevations into the predawn-morning as the air saturates from the top downward.  Light winds, then SSE-SW at 5-10 mph, with higher gusts, on mid-upper elevation mountain ridges toward morning.  Temps dropping into the 20s to around 30 degrees, with lower wind chills on higher ridges by morning.

Saturday Morning Through The Afternoon

Snow becoming mixed with or changing to sleet, rain or freezing rain.  Winds SE to SSW at 5-10 mph, with higher gusts, on middle-upper elevation mountain ridges and exposed plateaus.  Damp and raw with temperatures in the mid-upper 30s.

Saturday Night Into Sunday Morning

Mainly rain.  Freezing rain remaining possible in upslope locations at upper elevations in the High Knob Massif.  SE to S winds 5-15 mph, with higher  gusts, below 2500 to 3000 feet.  SSE-S winds 10-20 mph and gusty at upper elevations.  Temperatures widespread in the 30s.  Areas of fog and low clouds, especially at upper elevations.  Wind chills in the 20s to lower 30s, except 10s in gusts on higher peaks.

Sunday Afternoon-Early Evening

Rain or freezing rain changing back to snow at upper elevations first, then within middle-lower elevations by late in this period.

Dropping cloud bases with fog becoming dense at middle to upper elevations along and north of the High Knob Massif-Tennessee Valley Divide.  Light winds shifting NW-N at mainly 10 mph or less.

Temperatures dropping into upper 20s to mid 30s.

Sunday Night Into Monday Morning

Light snow and snow showers.  Freezing fog at mid-upper elevations along and north of the High Knob Massif-Tennessee Valley Divide.  NW winds mostly less than 10 mph.  Temperatures dropping into the middle-upper 20s, varying from low 20s at highest elevations in the High Knob Massif to lower 30s in downslope locations toward the south.

*Snowfall Forecast – Saturday To Monday

Up to 1″ at elevations below 2500 feet

Up to 2″ at elevations above 3000 feet

Target Snowfall of 0.5″ to 1″ in Norton-Wise area (+/-) 0.5″ error potential, suggesting a dusting to 1″ possible during entire event.  This is a relatively low confidence forecast.

Snowfall totals are for locations along and northwest to northeast of the High Knob Massif-Tennessee Valley Divide, with lesser amounts expected to generally fall toward the south within downslope locations of the Clinch, Powell, and Holston valleys.

*Stay tuned for later adjustments depending upon how the system evolves into Sunday.

 

Weather Discussion ( Miller B = Nasty )

Saturday Afternoon Update

Following a light coating of snow into Saturday AM across northern parts of Wise, Dickenson & Buchanan counties the day has featured a break and widespread temperatures hovering in the 30s to near 40.

While snow began falling on High Knob between 1-2 AM Saturday, subsequent precipitation evaporated as dewpoints tanked ( going sub-zero ) to suggest that sinking air aloft was being generated and completely missed by forecast models which predicted saturation from top to bottom over time.

 Based upon new model runs today I have greatly reduced snow amounts into Monday; however, this continues to be a low confidence forecast setting.

Using past climatology of Miller B systems, rain should dominate from this point forward westward of the cold air damming wedge, with a transition back to snow as winds shift northerly in direction late Sunday into Monday.  Since this system will not deepen into a Nor’easter,  snow amounts should remain light and limited in backside upslope flow.

A notable exception to the above being a continued threat of icing at upper elevations in the High Knob Massif where air temps-dewpoints remain supportive of freezing rain, which I have left in my forecast for upper elevations.

Outside of freezing rain, there is nothing worse and more nasty than a cold rain during winter with air temperatures in the 30s.  NASTY! 

 

Previous January 11 Discussion

The upcoming winter storm is forecast by models to take on characteristics of a Miller B system.  My past climatology of such storms can be summarized by a single word.  NASTY.

Miller B storms tend to throw everything but the proverbial kitchen sink down on the mountain area, and this event will be no different if it does indeed conform to this type of winter storm.

By nature, Miller B events tend to be among the most difficult to forecast with respect to specific amounts of any given precipitation type.

Some Miller B storm systems become Nor’easters.

Some Miller B storms ( like this one ) take a trajectory which carries them outward into the Atlantic Ocean and do not turn up the coast toward New England.

A large difference in snowfall amounts between the NAM 12 KM and its high-resolution 3 KM sibling can be used to illustrate the forecast difficulties.

The 12z run of the operational European Model and many ensembles are closer to the NAM 12 KM locally, but more like the NAM 3 KM toward the south where it transports more above freezing air aloft across the Tennessee Valley and southern Appalachians.

The European Model group and the NAM 3 KM are predicting a setting for  significant icing across much of North Carolina versus the GFS-FV3 and NAM 12 KM . 

The new GFS-FV3 looks too heavy over the Carolinas and more on target for the Greenbrier Valley region of southeastern West Virginia where past climo on Miller B storms shows a maximum in snow.

Totals of frozen precipitation types within upper elevations of the High Knob Massif also tend to be greater than generally indicated by models in this type of Miller B storm setting.

 

Government Shut-Down & USA Models

Is the current government shut-down impacting daily forecasts in the USA?

The  National Weather Service Is Open BUT

It should not in theory, but since high-resolution USA models use the GFS domain it is problematic.  It is not surprising that the GFS has generally struggled with rather significant inconsistencies and it is scheduled for a replacement upgrade to a new dynamical core being called the FV3 for Finite Volume Cubed-Sphere.

While the GFS-FV3 has been in testing mode, it is not yet the official USA model domain for running of the high-resolution terrain models.

The ECMWF and its ensemble mean has been my favored medium range model since I first began using it during the early 1990’s; however, being global in nature it is not designed for detailed topographic resolution.

No model ever generates a totally perfect forecast, especially in complex terrain settings, and all must be adjusted to best fit local terrain and climatology. 

Yet, the better a model performs the better any forecast can theoretically become.

A mostly unspoken factor, but extremely valid, is stress-strain this is putting upon employees of the National Weather Service and their families.  This entire aspect is simply wrong.

Members of the NWS are professionals and while they typically carry onward this is not their fault and they should not be penalized for their public service which, unfortunately, they typically do not receive the credit they deserve even without a shut-down.

 

Cold Blast of January 10-11

Temperatures plunged into the single digits and 10s with this first major cold blast of January 2019, not including wind chills, with a large vertical spread developing this morning ( Friday Jan 11 ) between rising readings into 20s on high mountain ridges versus temps dropping toward 0 degrees in high valleys ( hovering near 10 degrees in Clintwood ).

MAX temperatures January 10 did not rise above lower-mid 10s at highest elevations in the massif, versus mid-upper 20s around Wise and Clintwood.

This was the first cold frontal passage in months, if not longer, to transport limited moisture.

A dusting up to 1″, with most of the area only having a dusting of snow, was observed as the bulk of Great Lake moisture remained northeast of the area.

While I generally expected this, and noted it on my previous forecast page, moisture was a little slower to arrive on Wednesday and slower to leave upslope sides of the mountains on Thursday.

The local mountains were on the southwest edge of the moisture field into Thursday afternoon, with clouds banking up against the Wise County side of the High Knob Massif ( Scott-Lee Counties cleared ) versus clouds which extended farther southeast as air toward the northeast of the massif was not being lifted as efficiently ( allowing solid clouds to reach southeast to the Brumley-Garden mountain area )  nor sinking leeward as vigorously on NNW-NNE winds.

Weather Headlines ( January 7-13 )

ALERT For Accumulating Snowfall Beginning Wednesday Afternoon Into Thursday Morning Within NW Flow Upslope Zones Along And Northwest Of The High Knob Massif & Tennessee Valley Divide

Flurries and snow showers will begin developing during Wednesday afternoon and continue into the mid-morning hours of Thursday.  Caution for slick sections on roadways, with accumulations varying from a dusting up to 2″+ .

ALERT For Strong WNW to NW Winds And Bitter Wind Chills Wednesday Into Thursday – Especially Middle To Upper Elevations.  Caution is advised. 

Strong SSE-SW winds will develop Monday into Monday Night well in advance of a strong cold front.  Wind gusts of 25-40+ mph will be common in upper elevations & exposed mid elevation ridges-plateaus.

A strong and steady temperature decline will begin Tuesday Night and continue into Thursday Morning, with steady to falling temperatures expected during Wednesday as low-level moisture begins increasing.  Strong & gusty WNW-NW winds will make conditions feel much colder with dropping wind chill values.

ALERT for a blast of bitter cold with temperatures falling slowly through the 20s Wednesday at the middle to lower elevations along and northwest of the High Knob Massif, through the lower 20s into the 10s at upper elevations.

Expect much colder wind chill values.

NW flow snow showers and flurries are expected by Wednesday PM into Thursday AM on upslope flow.  Accumulations are expected to be light, with greater Great Lake moisture transport farther northeast in central-northern West Virginia into Pennsylvania.

The potential for a more widespread and significant winter storm system is being monitored for January 12-13.  Stay tuned for later updates.

Mountain Area Forecast ( Jan 9-11 )

Tuesday Night Into Wednesday Morning

Partly-mostly cloudy.  Windy and colder.  Winds W-NW at 10-25 mph with higher gusts.  Temperatures dropping into the lower 20s to the lower 30s, coldest at highest elevations.  Wind chills falling into the 20s and 10s, except single digits at highest elevations.

Wednesday Mid-Day Through The Afternoon

Mostly cloudy.  Windy & cold.  Flurries and snow showers developing.  Temperatures falling slowly through the 20s at middle-lower elevations, and 10s  at upper elevations, along and northwest of the High Knob Massif & Tennessee Valley Divide.  Milder in the downslope locations toward the south.  Wind chill factors in the 10s to lower 20s at elevations below 3000 feet and in single digits to 10s above 3000 feet.  Wind chills dropping below zero highest elevations. Riming at highest elevations.

Wednesday Evening to Mid-Morning Thursday

Snow showers, with a snow burst possible, tapering to flurries.  Windy and bitterly cold.  NW-NNW winds at 10-20 mph with higher gusts.  Temperatures varying from single digits at highest elevations to the mid-upper 10s.  Wind chills 0 to 15 degrees at low-middle elevations and 0 to -15 below at upper elevations.  Riming at highest elevations.

Mid-Morning Thursday Through The Afternoon

Clouds and any flurries giving way to partly sunny skies ( mid-high clouds ).  Unseasonably cold.  NW winds 5-15 mph with higher gusts.  Temperatures varying from mid-upper 10s to middle-upper 20s.  Wind chills varying from single digits to low 20s, except below zero in gusts on highest peaks.

Thursday Night Into Friday Morning

     Partly-mostly clear.  Winds shifting N at 5-10 mph, with some higher gusts, on middle to upper elevation mountain ridges.  Temperatures falling into the single digits & 10s, except locally colder in coldest mountain valleys at upper elevations.

Mountain Area Forecast ( Jan 2-5 )

Rain will change to snow at highest elevations late Friday night into Saturday morning.  Caution for a few slick patches, mainly above 3300 feet, into the early morning hours of Saturday ( Jan 5 ).  

Wednesday Night Into Thursday Morning

Evening showers and areas of drizzle giving way to soaking rain.  Breezing to gusty S-SW winds shifting W-NW and decreasing to 5-10 mph with some higher gusts.  Temperatures dropping into the 30s to lower 40s ( coolest at highest elevations ).  Low clouds with areas of fog, becoming widespread upper elevations. 

Wind chill factors in the 20s to lower 30s at upper elevations and the 30s to low 40s at middle to lower elevations ( mainly along mountain ridges and exposed plateaus ).

Thursday Morning Through The Afternoon

Morning rain and low clouds giving way to mid-high clouds.  Light NW-N winds becoming westerly at high elevations.  Temperatures in the 30s to middle 40s.

Thursday Night Into Friday Morning

Mostly cloudy ( mainly mid-high altitude clouds ) evening skies giving way to lowering cloud bases with rain developing into the predawn-morning.  Winds becoming SE-S and increasing to 5-15 mph, with higher gusts, mid-upper elevation mountain ridges. 

Temperatures in the 30s to lower 40s, steady or rising overnight into morning.  Areas of low clouds and fog developing ( especially at high elevations ).

Friday Morning Through The Afternoon

Morning rain giving way to showers.  Breaks in clouds during the afternoon, especially west to north of the High Knob Massif.  Unseasonably mild.  Winds SE-S at 10 to 20 mph, with higher gusts, at elevations below 2700 feet.  Winds SSE-SSW at 15-25 mph with higher gusts above 2700-3000 feet.  Temps in the 40s to mid-upper 50s.  Low clouds-fog at highest elevations.

Friday Night Into Saturday Morning

Windy & turning colder.  Evening rain showers changing to snow at upper elevations, becoming mixed with or changing to snow showers or mix at middle elevations and becoming mixed with snow or sleet at lower elevations.  Winds shifting SW to WNW at 10-25 mph, with higher gusts, on mountain ridges and exposed plateaus.  Temperatures dropping to around 30 degrees at highest elevations to the mid 30s to around 40 degrees.  Wind chills dropping into the 20s to lower 30s, except 10s in gusts highest peaks.

Snow accumulations of a dusting up to 1-2″ will be possible, mainly at elevations above 3300 feet.

Saturday Morning Through The Afternoon

Morning clouds giving way to mostly sunny skies.  Gusty and seasonally cool.  Winds W-NW at 10-20 mph with higher gusts.  Temperatures mainly in the 40s, with 30s at highest elevations during much of day.  Wind chill factors in the 20s and 30s. 

 An increasingly cold weather pattern is being monitored for the extended 6-10+ day period.  Stay tuned for later updates on a return of wintry conditions.

Weather Discussion ( Winter Not Dead )

Lovers of snow and cold weather should not despair despite a mild, wet beginning to 2019.  In fact, severe winter conditions remain likely to develop in coming weeks across the eastern USA.

Reference Wetness Of 2018 for a few highlights of 2018.

New Year Day 2019 marked not only the beginning of another year but the official designation of a major sudden stratospheric warming above high latitudes within the Northern Hemisphere.

Winds at 10 mb and 60 degrees North must change from westerly to easterly ( blue color above ) and the temperature gradient must become positive in order to meet the technical criteria adopted by the World Meteorological Organization for a Major Mid-Winter Warming or SSW ( Sudden Stratospheric Warming ) event to be designated.

This is an exciting development for meteorologists in the research fields, and a look back at last winter can illustrate why this is so important.

SSW = Sudden Stratospheric Warming

During the 2017-18 winter ( red line above ) a minor stratospheric warming aided an arctic blast which started 2018 as the Polar Vortex temporarily became weaker and the polar jet developed high amplitude.

The Polar Vortex then became stronger in January 2018 with a significant increase in zonal mean wind speeds ( upward spike in red line above ).  A mild and record wet February followed locally as changes at high latitudes generated a major SSW event and the Polar Vortex weakened in February with reversal of winds to easterly ( red line dips below zero above ).

Locally, March into April turned wintry and conditions during March 2018 were colder than February.

Major warming of the stratosphere came late in the winter season last year, with impacts locally being felt during March-April after they propagated down from the stratosphere to impact weather conditions within the troposphere.

This winter a record-level heat flux associated with current major SSW has occurred early in the winter season, with upcoming changes having the potential to be much more significant in terms of tapping air that is much colder ( forming amid darkness at high latitudes and being yet unmodified by rising solar angles ) in nature and transporting it southward.

Every SSW event tends to be different with varied results for middle latitudes, yet it must be recognized that these events tend to increase odds of conditions turning bad in mid-latitudes.  This can result in late season wintry conditions which are bad for the time of year or severe conditions that can occasionally result in extreme events like happened later in January 1985 following a major SSW.

Reference Great Arctic Cold Wave of Jan 1985

Mountain Area Forecast ( Dec 30-Jan 1 )

ALERT For Strong S-SW winds Developing Monday Into New Year Eve_Beginning At Highest Elevations Early And Mixing Down into Middle-Low Elevations 

An increasing pressure gradient will drive strong winds across the Cumberland Mountains during Monday into New Year Eve, with S-SW gusts of 30-40+ mph ( especially on mid-upper elevation mountain ridges-exposed plateaus ).

Sunday Night Into Monday Morning

Evening high cloudiness, then increasing clouds overnight with rain developing toward morning, especially along and west-northwest of the High Knob Massif and Tennessee Valley Divide.  Areas of fog-low clouds developing.  Winds SSW-WSW at 5-15 mph with higher gusts along mid-upper elevation mountain ridges.  Temperatures varying from 30s in colder mountain valleys during the evening ( then rising overnight ) to the 40s to around 50 degrees.

Monday Morning Into New Year Eve

 Morning rain & showers giving way to partly-mostly cloudy skies ( mostly cloudy in upslope areas of the High Knob Massif to partly sunny in downslope sites of northern Wise, Dickenson-Buchanan counties ).  Windy and unseasonably warm.  S to SW winds increasing to 15-25 mph, with higher gusts, below 2700 feet.  Winds SSW-WSW at 20-35 mph, with higher gusts, on mountain ridges above 2700-3000 feet.  Temperatures varying from low 50s at high elevations to the mid-upper 60s.

The Storm Prediction Center has issued a marginal risk of severe thunderstorms along and west of the Cumberland Mountains & Cumberland Plateau for December 31.

New Year Eve Into New Year Morning

Cloudy & windy.  Rain developing.  Downpours with a chance of thunder during the evening giving way to partly cloudy skies overnight-toward morning. Fog possible in valleys sheltered from wind.  SW winds shifting W-WNW and decreasing to 5-15 mph with higher gusts by morning.  Temperatures falling into the 40s to around 50 degrees.

New Year Day

Partly-mostly cloudy.  Breezy & cooler.  Winds WNW-N at 5-15 mph with higher gusts.  Temperatures nearly steady to slowly falling in the 40s at middle to lower elevations along and north of the High Knob Massif-Tennessee Valley Divide ( falling into 30s at highest elevations ).  Wind chills in the 30s to lower 40s, except 20s at highest elevations in gusts.

Possible development of dense fog is being monitored for late New Year Day into New Year Night-Wednesday AM as cloud bases lower on upsloping N winds and cool advection in places along-north of the High Knob Massif-Tennessee Valley Divide.  Stay tuned for a possible alert.

The track of an upper-level low and cold pocket aloft is being monitored for possible accumulating snow by the January 4-5 period.

Weather Discussion ( A New Year )

An active but unseasonably mild weather pattern is closing out the soggy year of 2018, as a Major Sudden Stratospheric Warming ( SSW ) event is underway at high altitudes in the stratosphere.

Conditions in the troposphere and stratophere are not unrelated.  Waves originating within the troposphere have rippled upward into the stratosphere where their breaking has resulted in releases of energy and momentum ( raising air temps ).

Waves from the troposphere began reaching well into the stratosphere during Autumn 2018, with a recent record high amplitude achieved in December ( above ) and a subsequent elevation in temperature as waves lift the air aloft to cause warming.

The lapse rate in the stratosphere tends to be negative or directly opposite to that in the troposphere, such that rising air warms instead of cooling with increasing height.  Waves that lift air in the stratosphere cause warming ( below ).  

Breaking of tropospheric waves in the stratosphere also releases momentum, slowing and even changing the speed and direction of flow ( below ).

The Bottom Line…

The beginning of January 2019 will be a highly transitional period and models will tend to struggle, as recently observed, more than usual given that changes occurring both horizontally and vertically, from the stratosphere to troposphere, will now have to be resolved in order to make accurate forecasts.

I expect more dependable and clear forecasts into the medium range to emerge as this troposphere-stratosphere-troposphere coupling continues to cycle and changes now underway within the stratosphere work down into the troposphere during the next couple of weeks.

 As this major SSW event continues, a changing MJO    or Madden-Julian Oscillation will be moving through phases 5-6 into phases 7-8-1 during January 3-13.

The progression of the MJO from the warm phases of 5-6 into the colder phases of 7-8-1 will be occurring during the January 3-13 period.

If the European Model is correct this suggests that cooling will intensify after January 5-7, so time will tell how all these factors interact with a Modoki El Nino ( central Pacific based warm anomalies ).

Model differences into mid-January are currently exemplified by the 51-members of the European group which predict snow amounts varying from nearly nothing to excessive depths.

Stay tuned for later updates.

Caution For Areas Of Fog Developing Friday Night Into Saturday Morning At Middle-Lower Elevations

Areas of fog, drizzle, and light rain showers will continue into the overnight hours of Saturday.  Orographic clouds will be widespread at upper elevations.

Former Alerts

Weather ALERTS ( December 27-30 )

ALERT For Strong SSE to SW Winds Developing Thursday Into Friday ( December 27-28 )

While strongest general wind speeds will be experienced at middle to upper elevations, mountain waves are expected to produce powerful wind gusts in localized locations where waves break downward on northwestern sides of major mountain barriers.

A strong pressure gradient will drive strong SSE-S winds across the mountains beginning early Thursday at upper elevations and working downward into middle to lower elevations during Thursday afternoon into Friday.

A period of strong SW winds are expected to develop behind a frontal passage on Friday into the Norton-Wise area and mid-upper elevations along the High Knob Massif and Tennessee Valley Divide.

ALERT For Heavy Rainfall, Strong Rises And Possible Flooding On Streams During Friday Into Friday Night

The first of multiple waves will spread heavy rainfall across the mountains Friday.  A Flash Flood Watch Is Now In Effect Through Friday Afternoon.

Updated_Friday Afternoon_December 28

Water levels rises are expected to remain safely below flood stage through Friday into Saturday.

A general 1.00″ to 1.50″ of rain, with locally higher amounts, was less than predicted by models and this will keep stream levels below flood stages ( 0.50″ to 2.50″ being the general rainfall extremes ).

Downstream convection, with up to 12.00″+ of rain along the Mississippi-Louisiana border, was partly responsible for less total rainfall to the northeast.

Melting of high water content snow cover at upper elevations will be adding to run-off from rainfall during Friday into Friday night within places along and downstream of the High Knob Massif, Black Mountains, and other high mountain locations impacted by the December 21 winter storm.

Mountain Area Forecast ( Dec 27-29 )

Thursday Night Into Friday Morning

Rain showers early, then rain developing.  Windy. Downpours likely.  Thunder possible.  Winds SSE-SSW 15 to 35 mph, with higher gusts ( gusts 40-50+ mph at upper elevations and mountain wave zones ). Temps varying from low 40s to low 50s.  Areas of dense fog developing overnight into early morning.  Wind chill factors in the 30s along high mountain ridges ( locally below freezing on highest peaks ).  

Friday Morning Through The Afternoon

Rain, heavy at times.  Thunder possible.  Rain tapering to showers during the afternoon.  Winds shifting SSW-SW at 10-25 mph, with higher gusts.  Temperatures in the 40s to low-mid 50s ( coolest in upper elevations and mildest in downslope areas of northern Wise and Dickenson counties ).  Areas of dense fog, widespread at upper elevations and in the SW flow upslope zone of the High Knob Massif-Tennessee Valley Divide.

Friday Night Into Saturday Morning

Low clouds.  Chance of drizzle.  Areas of dense fog, widespread at the upper elevations.  Turning chilly.  Winds shifting W-NW at 5-15 mph with higher gusts. Temperatures varying from around 30 degrees at highest elevations to around 40 degrees.  Wind chills in 20s & 30s, except 10s in gusts at high elevations.

Saturday Afternoon

Partly cloudy.  Light & variable winds, except SSW-WSW at 5-10 mph and gusty at highest elevations.  Temperatures in the upper 30s to mid-upper 40s, coolest highest elevations.

Wind chill factors in the 20s to lower 30s at highest elevations.

A second upper-air disturbance will trigger more moderate-heavy rains late in this weekend and early next week.  Water level rises will again need to be closely monitored.

This has been well depicted by the 51-member ensemble mean of the European Model group. There is increasing concern for another important, heavy rain producing wave of moisture to impact the mountains late this weekend into early next week.  This is likely to NOT be the final wave in this series of storm systems, with a trend toward colder conditions late in the 7-10 day period.

Please stay tuned for later updates.

Weather Discussion ( Worrisome )

While the short-term period is a concern, of course, I am especially concerned about the big-picture of the pattern upcoming through the next 7+ days.

A positive-tilted upper trough and SW flow aloft is climatologically favorable for heavy precipitation when it changes slowly over time with multiple short waves moving through the long-wave flow regime in this part of the world.  In addition, this is especially true for transitional periods when the synoptic-scale flow pattern is changing from warm to cold ( or cold to warm ).  In this case, the pattern will be undergoing a transition from milder to colder conditions over time.

Add to this anomalously wet antecedent conditions and the ingredients are present for serious problems to develop at any point from now into next week.

Short-range Model Predictions

While strong mountain waves are running on SSE flow in the low-levels, there will be a considerable SSW-SW flow developing at mid-upper elevations into the overnight-morning hours of Friday.

This type of strong change in wind speed and direction ( shear ) enhances convergence in the lower troposphere and often means rainfall amounts are heavier in locations west of the Blue Ridge versus when SE-SSE flow extends upward ( is vertically deeper ) through middle-upper elevations of the mountains.

The high resolution NAM model has been one of the most consistent with placement of the heavy rainfall axis, which will largely dictate what zones will have the greatest high water risk through the short-term.

The GFS Model has been tending to shift the axis of heaviest rainfall toward the northwest, along and northwest of the Cumberland Mountains.

This is similar to the high-resolution NAM.

The European Model has also been relatively consistent through past days, with a tendency toward increasing and shifting the main axis of heaviest rains to the northwest along the front range of the Cumberland Mountains and adjacent plateau.

Given a convective tendency with this system on the synoptic-scale plus an anomalous surge of tropical moisture in advance of an approaching upper wave the placement of heaviest rains can change due to convective influences downstream.

If the axis of heaviest rain does not develop where the high-resolution NAM Model predicts it is not because the model has not been consistent.

The High-Resolution Rapid Refresh ( HRRR ) model is generally in line with the high resolution NAM.

The crunch-time window will be Midnight to Noon for counties along the Cumberland Mountains and VA-KY border, with water level rises expected to continue for a period after rain diminishes during Friday PM.

The new run of the GFS has shifted a little southeast with the axis of heaviest rain, but continues to have it located across far southwestern Virginia into the adjacent sections of Tennessee.

There Is Now Increasing Concern About A Developing Upper Air Flow Pattern Which Could Generate Heavy-Excessive Rainfall From Late December Into The First Week Of January 2019.  ALERTS May Be Needed.

Former Alerts – None Currently Active

ALERT For The Possibility Of Slick Patches Developing On Roadways Late Sunday Into Sunday Night And The Morning Of Christmas Eve Day ( Beginning At Highest Elevations And Dropping Into The Overnight )

Rain & snow showers will develop across the area this afternoon and continue into tonight with falling temperatures.  Slow down and travel safely.

ALERT For Areas Of Dense Fog – Widespread At The Upper Elevations Sunday PM Into Monday Morning

Christmas Holiday Forecast ( Dec 23-26 )

Sunday Afternoon

Cloudy with rain showers developing.  Rain mixing with & quickly changing to snow at elevations above 3300 feet.  Rain mixing with or changing to snow at middle to lower elevations after sunset.  Winds SSE-SSW shifting WNW at 5-15 mph, with higher gusts, below 2700 ft. Winds SSW becoming WNW at 10-20 mph and gusty at elevations above 2700-3000 feet.  Temperatures in the 30s to lower 40s, dropping to around 30 degrees at high elevations by late.  Wind chills in the 20s & 30s, except 10s at upper elevations in gusts.  Areas of fog ( widespread at the upper elevations ).

Snowfall Forecast ( Sunday PM-Monday AM )

Generally a dusting up to 1″

Locally 1″ to 2″ above 3300-3500 feet

Sunday Night Into Monday Morning

Any mix changing to snow showers & flurries.  WNW winds 5-15 mph, with higher gusts, below 2700 feet.  Winds WNW-NW 10-20 mph and gusty above 3000 ft. Temperatures varying from mid-upper 10s to the mid to upper 20s by morning.  Wind chills in single digits and 10s on mid-upper elevation mountain ridges, except below zero in gusts on highest peaks.  Fog widespread at upper elevations with riming.

Monday Morning Through The Afternoon

Morning clouds and any flurries giving way to mostly sunny skies.  Seasonably cold.  Winds WSW-WNW at 5-15 mph with higher gusts.  Temperatures varying from 20s at upper elevations to the mid-upper 30s.  Wind chills in the 10s and 20s.

Christmas Eve Into Christmas Morning

Mostly clear early then increasing mid-high level clouds.  Cold.  Light & variable winds.  Temperatures varying from 10s to low 20s mountain valleys to the 20s, steady or rising late to near 30 degrees on well exposed mountain ridges-plateaus.

Christmas Morning Through The Afternoon

Partly to mostly cloudy.  Slight chance of a sprinkle, flurry, or mixture.  Winds SSW-SW at 5-10 mph with some higher gusts ( windiest on mountain ridges ). Temperatures varying from around freezing at the highest elevations to the low 40s.  Milder south into river valleys of the Clinch, Powell, Holston.

Christmas Night Into Wednesday Morning

Partly to mostly clear. Cold.  Light & variable winds. Temperatures varying from 10s in colder mountain valleys to the 20s ( around 30 degrees on exposed mountain ridges ).

Christmas History ( 1955-2017 )

 

*A wet extended range pattern is being watched which could bring an important flood threat to the mountain region from the end of December into the first week of January 2019 ( ahead of much colder air ).

Stay tuned for updates.

Weather Discussion ( Active Pattern )

This active weather pattern will not even take a break for the Holidays, with an array of systems lined up to impact the mountain region between Christmas Day and New Year’s Day.

A couple of minor systems, Sunday into early Monday and again later on Christmas Day, will occur as temps rise and fall with these passing waves.  Any sticking snow is expected to be light and mostly at the upper elevations ( where significant snow is covering the ground and a White Christmas is now certain* ).

*Mainly at elevations above 2800 feet.

A temporarily milder pattern is coming between Christmas and New Year Day, with December 27-30 currently being the period to monitor for significant rainfall.  Given snow melt at upper elevations, plus antecedent conditions, this will likely cause more strong water level rises and possible flooding.

Another system will be developing within a upper air flow regime conducive to heavy-excessive rainfall in the 5-10 day forecast period, from late December into the first week of January 2019.

Stay tuned for later updates on these systems.

Reference Look Ahead on my 122018 Forecast page to see how near-term warming may change around in a big way heading into January and February.

Mountain Area Forecast ( Dec 20-23 )

ALERT For Streams Around Flood Stage

At 3:15 PM the stream gauge on Big Stony Creek of the High Knob Massif was only 0.2 feet below flood stage.  Caution is advised along and downstream of steep creeks draining the High Knob Massif into Friday night.

ALERT For Strong Rises On Steep Creeks Draining The High Knob Massif Thursday Night Into Friday And On Other Streams Across The Area

Moderate to heavy rain will overspread the mountain landscape Thursday afternoon, with intervals of rainfall expected into Friday when a transition to snow will occur from TOP to Bottom ( from high to lower elevations ).

ALERT For Accumulating Snow Friday Into Friday Night-Saturday Morning With Hazardous Travel Developing From High To Low Elevations

Expect A Period Of Heavy, Wet Snow

A change from rain to snow is expected to begin at highest elevations in the High Knob Massif and to rapidly drop into middle elevations between mid-morning & early afternoon, then into lower elevations north of the High Knob Massif and Tennessee Valley Divide.

Note that power outages can not be ruled out in locations having heavy, wet snow.

*Snowfall Forecast ( Friday-Saturday AM )

General 1″ to 4″ below 2500-3000 feet

General 4″ to 8″+ above 2500-3000 feet

Target Snowfall of 4″ for Norton-Wise (+/-) 1″ error potential.  This implies a potential snowfall range of 3″ to 5″ for the Norton-Wise area, with locally heavier amounts possible.  Snowfall amounts of 1-2″ or less are expected in locations downstream of the High Knob Massif on WNW-NW-N air flow.

*Applicable to locations along and north of the High Knob Massif and Tennessee Valley Divide with moderate-strong orographics for the heavier snow amounts.

UVA-Wise professor and herpetology-wetlands expert Wally Smith highlighted slick road conditions during Friday afternoon snow on the Wise Plateau.

Overnight Into Thursday Morning

Increasing mid-high altitude clouds.  Winds SE-S at 5-15 mph with higher gusts on mountain ridges and exposed plateaus below 2700 feet.  Winds SSE-SSW at 10-20 mph, with higher gusts, on mountain ridges above 2700 feet.  Temperatures varying from upper 20s to low 30s in colder valleys ( tending to rise toward morning ) to the 40s on exposed mid-upper elevation mountain ridges.

Thursday Morning Through The Afternoon

Lowering & thickening clouds with rain developing.  Rain may be heavy at times.  Winds SE to SSE at 10-20 mph with higher gusts, especially over mid-upper elevation mountain ridges.  Temperatures generally in the 40s.  Wind chills in the 30s at upper elevations.  Low clouds with widespread dense fog at upper elevations ( especially along and SE of windward slopes ).  Areas of fog in other locations.

Thursday Night Into Friday Morning

Rain and intervals of showers.  Areas of dense fog, becoming widespread at middle to upper elevations.  Winds shifting SSW-W at 5-15 mph, with higher gusts, below 2700 feet.  Winds SW-W at 10-20 mph with higher gusts on ridges above 2700 feet. Temperatures falling into the 30s to lower 40s.  Wind chills falling into the 20s & 30s ( coldest at upper elevations above 3000-3500 feet ).

Friday Morning Through The Afternoon

Rain becoming mixed with and changing to snow from upper elevations into middle elevations, then into lower elevations north of the High Knob Massif by late.  Winds WNW-NW at 10-20 mph, with higher gusts.  Temperatures falling into the 20s at upper elevations and to around freezing in Norton-Wise by late afternoon.  Winds chills dropping into 10s & 20s.  Low cloud bases with riming at upper elevations.

Early Friday Evening Update ( below ).

Friday Night Into Saturday Morning

Evening mix or valley rain-drizzle giving way to snow and snow showers.  Turning colder into the overnight.  W-NW winds 10-20 mph with higher gusts on mountain ridges below 2700 feet.  WNW-NW winds 15-30 mph, with higher gusts, on mountain ridges above 3000 feet.  Temperatures dropping into the lower 20s to lower 30s.  Wind chill factors dropping into 10s & 20s, except single digits to locally below zero in stronger gusts on highest peaks.  Rime formation at upper elevations.

Saturday Morning Through The Afternoon

Morning snow showers & flurries giving way to partly-mostly sunny skies.  Winds becoming W-SW at 5-15 mph with higher gusts.  Temps varying from upper 20s to low 30s to the upper 30s to low 40s ( coolest at upper elevations and mildest in valleys with bare ground ).  Wind chills in the 10s and 20s by afternoon, colder during the morning hours, especially in gusts.

Saturday Night Into Sunday Morning

Partly to mostly clear.  Large vertical temperature spread developing between colder mountain valleys and exposed mountain ridges.  Winds SSW-WSW at 5-15 mph on mid to upper elevation mountain ridges.  Temperatures varying  from 10s in colder valleys to steady or rising into the 30s  along higher mountain ridges.

*Colder air will return to the mountain area during Christmas Eve Day and later on Christmas.  A couple of upper air waves moving across the mountains will offer the chance for snow showers & flurries, with light accumulations possible in upslope locations.

Reference My Christmas History ( 1963-2017 )

Weather Discussion ( Major Storm )

Another major storm system is bringing multiple threats to the mountain area, with high water levels being observed on creeks draining the High Knob Massif in wake of 2.00-3.00″ of precipitation.

The stream gauge on Big Stony Creek was 0.5 (1/2) foot below flood stage at 2:15 PM ( below ) and had risen to just 0.2 feet ( 2.4″ ) below official flood stage by 3:15 PM on Friday.

A 0.76″ water content difference was observed between the automated rain gauge on Big Stony Creek and Eagle Knob at 4:27 PM on Friday and that actually may be a saving grace to keep water level rises under control as snow blankets middle to upper elevations of the higher terrain ( around 8″ at the summit level ).

The rain gauge water content difference above being mainly due to a change to snow on Eagle Knob ( 4196 feet ) as rain continued to fall on Big Stony Creek ( below 1500 feet ).

An interesting snowfall gradient developed in the vertical with this system, with a change to sticking snow at the summit level of the High Knob Massif between 9:30 to 10:00 AM Friday.

Snow began falling at UVA-Wise around 11:30 AM.

Snow levels dropped to near 2000 feet and snow became heavier at mid-upper elevations into the afternoon of Friday.

Joe Fields measured 6″ of snow depth at his home in High Chaparral during a lull in snowfall at 4:30 PM Friday, with his wife Darlene highlighting the slick roads ( below ).

An little rise in temperatures during late afternoon into early evening of Friday occurred with transport of milder air ahead of a upper-air wave.  Once this passes cold air transport will develop and upslope snow showers will increase into the overnight of Saturday ( December 22 ).

Locations along and north of the High Knob Massif which were below sticking snow levels Friday will have a chance to accumulate some snow into early Saturday morning before the upslope diminishes.

 

Looking Ahead – Major SSW Event

In the near-term, a couple more upper air waves will cross the Appalachians to renew cold air transport into Christmas Eve Day and again late Christmas Day into December 26.  At the least, this will offer snow lovers a chance for more flakes ( help hold snow at mid-upper elevations on northern slopes ) and even offer some sticking snow for upslope locations.

A mean trough position over the eastern USA will be giving way to ridging as huge changes occur in the atmosphere above high latitudes in coming days.

These changes will be associated with a major sudden stratospheric warming (SSW) event.  Note how temps above the North Pole are predicted to rise ( below ).

The European Model is predicting a reversal of winds at 60 degrees North and 10 MB to meet the technical definition for a major SSW event.

Note the changes at 60 N and 10 MB in 10 days.

Note that the negative ( – ) blue color shades represent easterly wind speeds in meters per second, while the positive ( + ) tan-red colors represent the westerlies in meters per second.

Comparing the two plots above, winds at 60 degrees North and 10 MB go from being westerly at 27 m/s to easterly at 10 m/s for a complete reversal. 

While this will aid late month warming and major winter storm development in the Great Plains during the relative short-term, it is more likely to aid the development and southward surge of bitter arctic masses of air into middle latitudes into January and February, with the eastern USA being favored for severe winter conditions.  Stay tuned for updates.

Weather Headlines ( Dec 17-22 )

*Following low clouds into early Monday a period of drier air is expected to bring sunshine back into the afternoon.

Updated 2:00 AM December 18

*A shift to northerly winds will bring low-level cold air into the mountains Monday night into Tuesday.  While low-level moisture transport is generating some clouds in the upslope zone of the High Knob Massif, drier air aloft is looking to dominate.

*A seasonally nice mid-week gives way to a major storm system with rain developing by Thursday.  Locally heavy rain amounts will be possible.

*An ALERT For Strong Rises on Streams Will Likely Be Needed For Late Thursday Into Friday

A general 1.00″ to 3.00″ of total precipitation is expected with this system, including water content of snowfall.

*Colder air wrapping around the system will bring accumulating snowfall Friday into early hours of Saturday, with snow levels dropping from highest elevations downward over time.

A moderate-locally heavy accumulation of snow will be possible in locations along and north of the High Knob Massif and Tennessee Valley Divide.  Much less sticking snow, with 1″ or less, is currently expected within downslope locations lee of the High Knob Massif-Tennessee Valley Divide on NW-N air flow.

Preliminary Snowfall Forecast (Friday-Saturday AM)

General 1″ to 3″ below 3000 feet

General 3″ to 6″ above 3000 feet

Target Snowfall: 2″ in Wise (+/-) 1″ error potential.  This implies potential for 1″ to 3″ in the Norton-Wise area.

Rain will begin changing to snow at the summit level of High Knob by the sunrise to mid-morning period of Friday, with snow levels dropping to the elevation of Wise by mid-late afternoon.

Mountain Area Forecast ( Dec 17-19 )

Overnight Into Monday Morning

Low clouds.  Dense fog at upper elevations.  Areas of fog at middle to lower elevations.  Winds W-WNW at 5-15 mph on mountain ridges below 2700 feet.  WNW-NW winds 10 to 20 mph, with higher gusts, on mountain ridges above 2700 feet.  Temps varying from around 30 to near 40 degrees.  Wind chills within the 20s and 30s, except 10s in gusts along highest mountain ridges.

Monday Afternoon

Partly-mostly sunny.  Winds W-NW at 5-15 mph with some higher gusts.  Temperatures in the 40s, except some 30s at upper elevations.  Wind chills in the 30s to lower 40s, except 20s at upper elevations.

Monday Night Into Tuesday Morning

Partly cloudy.  Turning colder.  Winds NNW to NNE at 5-10 mph with some higher gusts.  Temps dropping into the 20s to around 30 degrees, except 10s in colder valleys at the upper elevations toward morning.

  Tuesday Afternoon

Partly to mostly sunny.  Seasonally cold.  Light northerly winds.  Temperatures in the 30s to low-mid 40s.

Tuesday Night Into Wednesday Morning

Mostly clear into the overnight, then some increasing high clouds.  Large vertical temp spread developing between the colder mountain valleys & milder ridges.  Winds S-SW at 5 to 15 mph on mid-upper elevation mountain ridges & plateaus.  Temperatures varying from 10s to lower 20s in colder valleys to the 30s to low 40s on exposed ridges-plateaus.

Wednesday Afternoon

Hazy sunshine ( high clouds ).  Winds SSE-SW at 5-15 mph with some higher gusts.  Temperatures in the 40s to low-mid 50s ( coolest in upper elevations ).

Wednesday Night Into Thursday Morning

Cloudy ( mid-high clouds ).  Winds SE-SSW at 5-15 mph with higher gusts along mid-upper elevation mountain ridges and exposed plateaus.  Temperatures in the 30s and 40s, coldest in sheltered mountain valleys and hollows.  Wind chills in the 30s along higher mountain ridges. 

Reference Major Winter Storm for updated information on the December 9-10 storm event.

Reference my History Of Christmases Past to review the past 55 years of weather history.

Weather Headlines ( December 13-16 )

Alert For Rises On Streams Into This Weekend

Strong Rises On Streams ( Steep Creeks ) Draining    The High Knob Massif

Updated Saturday Morning – December 15, 2018

Strong water level rises are now being observed on creeks draining the High Knob Massif ( ROARING water ).  Caution Is Advised.

As of 7:30 AM Saturday the stream level on Big Stony Creek was only 1.4 feet below flood stage, and is expected to rise more into the day.

Showers and intervals of rain will overspread the mountain area Friday into Saturday.  Due to slow movement of an upper-level low, precipitation will occur in broken intervals over an extended period   and is not currently expected to present a threat of significant flooding.  Stream levels are expected to rise into this weekend and should be monitored, especially in areas downstream of significant snowpack (e.g., High Knob Massif, Blue Ridge).

A period of snow will be possible late Saturday into Sunday AM for high peaks from the Great Smokies and Mount Mitchell northeast to Mount Rogers as a pocket of cold air aloft passes over the TN-NC border area with a slow moving upper-level low.  Snow-sleet will also be possible atop the High Knob Massif but sticking is currently looking limited on High Knob versus the highest peaks under the coldest air aloft that passes southeast of the Cumberlands.  

High density snow is difficult to melt, and I expect deep snow to linger at upper elevations in the High Knob Massif into this weekend, especially on northern slopes within basin heads of the Big Cherry Lake, High Knob Lake, and   the Norton Reservoirs.

The greatest threat in the High Knob Massif will not be total rainfall as much as it will be engulfing orographic clouds with latent heat of condensation release in saturated air ( a mild, saturated air mass is the greatest threat to rapid snow melt as exemplified in wake of the big January 1996 storm; however, at this present time I do not expect temperatures to be as warm over the snowpack as observed during January 1996 ).

Deep snow will be able to absorb and contain a significant amount of rain at high elevations, with a greater melt potential at lower-middle elevations which were impacted by heavy snowfall during this recent winter storm.  Until rainfall, temps, and fog extent are seen the amount of run-off will remain uncertain but problematic.

Update At 9:00 PM Friday ( December 14, 2018 )

An increase in run-off is beginning to be observed late Friday, so conditions will need to be closely followed through this weekend.

Fog Will Become Widespread And Dense Later Friday Into Saturday – Especially In Places With Snow Cover And Certainly At Upper Elevations Where A Prolonged Period Of Dense Fog Is Expected

Milder air moving over cold, snow covered surfaces will need to be monitored for the potential of widespread fog formation at all elevations (likely at upper elevations) later Friday into Saturday across the mountains.  A prolonged period with orographic clouds (low bases-dense fog) is expected at higher elevations above 2500-3000 feet.

A rather strong surface inversion has trapped cold air in hollows across northern Wise County, Dickenson County and portions of Buchanan County with 30s ( 35 degrees at the official NWS station in Clintwood at 9:45 PM Friday, following a MAX of only 37 degrees ).

A cold, damp, moisture laden air mass is bone-chilling and foggy, with increasing fog at mid-upper elevations.

Mountain waves of all forms-types tend to be common across the High Knob Massif on different air flow trajectories.

Wave forms are so common that essentially everything within the natural world can be described by waves, from sound and beating of the human heart to weather & climate parameters of all types.

Former ALERTS

ALERT For Local ICY Patches In Colder Mountain Valleys Into The Overnight Hours Of Friday

Temperatures amid colder mountain valleys have dropped below freezing ( 29 degrees officially at Clintwood 1 W at 10:00 PM ).  Caution for local icy patches is advised from refreezing with changeable conditions as temperatures vary from well above freezing in exposed locations to 20s with short-distance elevation changes.  Remember sensors like Norton ES are 15-20 feet above the ground and read warmer than closer to the snow and road surfaces.

*ALERT For Strong Winds Developing Friday At The Upper Elevations And Within Mountain Wave Zones

Wind speeds will increase overnight into Friday morning at upper elevations, with mountain waves breaking toward valley floors with locally strong gusts in favored areas.

*Sheltered locations at lower elevations will experience much lighter winds during this period.  Mountain wave gusts can be highly localized as waves may not always break completely to  valley floors with the High Knob Massif being so wide.

Mountain Area Forecast

Overnight Into Thursday Morning

Mostly cloudy.  Chance of a shower or sprinkles.  Freezing within colder locations. Gusty SW winds at 10-20 mph, with higher gusts, over middle-upper elevation mountain ridges and exposed plateaus.  Temperatures varying from 20s to lower 30s in colder locations to the mid-upper 30s to around 40 degrees on exposed middle elevation ridges and plateaus.  Wind chills in the 20s to lower 30s.

Thursday Afternoon

Mostly cloudy early with a decrease in clouds possible during mid-late afternoon.  Winds SE to S at 5 to 15 mph with higher gusts.  Temperatures varying from 30s in upper elevations to the 40s at low-middle elevations, except 50s in locations without snow cover from Powell Valley to Big Stone Gap and Pennington Gap.  Wind chill factors in the 30s to lower 40s, except 20s at high elevations in gusts.

Thursday Night Into Friday Morning

Increasing clouds overnight into morning.  Winds SE to SSE at 5 to 15 mph, with higher gusts, on mountain ridges below 2700 feet.  Winds SSE-SSW at 10-25 mph, with higher gusts, along mountain ridges above 2700 feet.

Temperatures varying in the 30s to lower 40s, except dropping into the 20s in valleys sheltered from evening wind ( tending to rise with increasing clouds overnight ).

Friday Morning Through The Afternoon

Cloudy with rain developing.   Chance of thunder.  Strong winds developing at upper elevations and locally amid mountain wave zones. Winds SE-SSE at 10-25 mph, with higher gusts, below 2700 feet. SE-SSE winds 25 to 35 mph, with gusts 40-50+ mph at the upper elevations and in mountain wave zones.

Temperatures varying from 30s sheltered hollows and low 40s at highest elevations to lower 50s.  Low clouds bases with widespread dense fog at the upper elevations and patches of dense fog at other elevations.  Wind chills in the 20s and 30s (coldest at highest elevations).

Friday Night Into Saturday Morning

Intervals of rain.  Low clouds and areas of dense fog.  Windy across mid-upper elevation mountain ridges.  SSE winds 5-15 mph with higher gusts below 2700 feet.  Winds SSE-SSW at 15-30 mph, with higher gusts, decreasing toward morning, above 2700 feet.  Temperatures mainly in the 40s, with localized 30s in sheltered mountain hollows.

Saturday Morning Through The Afternoon

Morning showers, possible mid-day breaks on the Wise County side of the High Knob Massif, then an increasing chance of mid-late afternoon showers.  Chance of thunder and/or local hail or graupel by late.  Sleet or mixed snow at the highest elevations.  Winds SSE-SSW at 5-15 mph, with higher gusts across mountain ridges.  Temps in the 40s to middle 50s, tending to drop at upper elevations during mid-late afternoon.  Wind chills in the 30s to low 40s at higher elevations.  Low clouds with dense fog at upper elevations, especially along the Scott County side of the massif.

Saturday Night Into Sunday Morning

Showers with a chance of thunder ( especially through the evening ).  Local hail or graupel.  Sleet-snow mix possible at the highest elevations.  Winds shifting SW-W at 10-20 mph with higher gusts.  Temperatures dropping into the 30s to low 40s. Wind chills in the 20s and 30s.  Low cloud bases with widespread dense fog at upper elevations and locally dense to widespread fog at lower-middle elevations.

Weather Discussion ( December 14-16+ )

A large overnight temp difference was observed into Friday morning with 32 degrees in Clintwood at 7 AM being colder than windy mountain peaks.

Strong wind gusts are being observed in local places, with speeds over 40 mph, to contrast with calm conditions in other locations, as mountain waves develop along the mountains from the High Knob Massif to Pine Mountain.

The standing waves will remain for hours, even though they may not always be visible as condensation moisture ( other clouds ) obscures them.

I removed 30s from my forecast on the update last night, but just added them back in this afternoon for sheltered hollows which have remained decoupled across northern Wise and Dickenson counties and  have held in the 30s all day Friday to create a large contrast with places having good mixing.

MAX temperature of 37 degrees at Clintwood 1 W ( 3:45 PM temp of 36 degrees ).  Temperatures are also in the 30s to lower 40s in the colder places within the High Knob Massif.

That illustrates sometimes the original idea on a forecast is correct and should not be changed.

I continue to expect fog to become more of an issue tonight into Saturday, perhaps dissipating some during the day, and increasing again in coverage Saturday night-Sunday.

Looking Ahead

Saturday is looking to be the mildest day before the Sunday-Monday period returns to chillier conditions with low clouds (low fog levels) and temps mainly in the 30s to low 40s beneath an inversion.  A nasty, raw feeling period.

A colder pattern is looking to return by the holiday period, so the chance for more snow will certainly exist.  Stay tuned for later updates.