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.

Weather Headlines ( Dec 7-11 )

ALERT For A Heavy To Crippling Fall Of Snow During Sunday ( December 9 )

Snowfall rates during the predawn to mid-day period of Sunday are currently targeted to be most extreme, with many roads likely becoming impassible.  Travel should be avoided and plans to be where you expect to stay Sunday should be made now.

Excessive Snowfall Alert For Mid-Upper Elevations of the High Knob Massif And Tennessee Valley Divide

This now includes the Norton-Wise Area

Prepare for impassible roads and the potential of power outages developing Sunday, especially in locations along and southeast of the VA-KY line, where snow depths of a foot or more will be likely.

ALERT For Blizzard Conditions At Upper Elevations In The High Knob Massif

Strong ESE-ENE winds, with gusts over 40 mph, will generate blizzard conditions and make all roadways impassible at upper elevations.

Forecast Model Discussion

The upcoming storm event will generate huge snowfall gradients, both regionally on the synoptic-scale ( or large scale ) and locally on the meso-scale ( or short distances ).

A general southward shift has been observed in the GFS and European models during the past 24-hours; however, not all ensemble members are so aggressive with pushing it south.  This southward shift is due to stronger High pressure to the north acting to suppress this classic snow storm track.

*The new GFS-FV3 has remained more consistent and farther north with the storm and heavy snow versus the operational GFS model ( as has the GEM noted below and the JMA continues to bring 10-12″ into the Wise area ).

Most forecasting mistakes are made by jumping onto such radical changes, instead of forecasting for the pattern and using past climatology as the reference with past analog storm events (well documented settings).

How models are struggling can be illustrated just today by differences between the 7 AM run of the NAM Model and its latest 1 PM run.

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Observe how snowfall at the Wise gridpoint varied from 2″ on the 7:00 AM run to 17″ on the 1:00 PM run (thus the problem at hand).

Of global-scale models the Canadian remains firm with a heavy hit, but this operational form can not resolve terrain features very well ( that requires the RGEM 48-hour model ).

The 12z European Model group (7AM Friday run) varied from less than 2″ to more than 12″ at the Wise gridpoint, with 5-6″ being the ensemble mean.  It is important to remember that snowfall in Wise tends to be underestimated by this model under the best of circumstances.

Saturday Afternoon Update ( Below )

Mesoscale Snow Depth Forecast

My forecast reflects excessive snow amounts, with a general 1 to 2 feet of snow expected from the Norton-Wise area upward into the high country of the High Knob Massif.  This will also include areas along the Tennessee  Valley Divide ( higher ridges-plateaus from Sandy Ridge and Hazel Mountain to Big A Mountain and the Black Mountains ).

Blowing & drifting snow will complicate this setting  at upper elevations in the High Knob Massif where depths may top 2 feet.

Snow amounts of 6-12″, with locally higher amounts, are expected at elevations below 2000 feet m.s.l. to the north toward Pound and Clintwood.

Snow amounts within the Powell River Valley and the Powell Valley corridor remain most problematic and will be largely dependent upon the development, or not, of a rain-snow transition zone.  If this develops amounts in this corridor will remain lower versus if precipitation remains all snow.

At this time my forecast is based upon downsloping on easterly air flow across the High Knob high country being supportive of a rain-mix transition zone developing over Powell Valley, with a TIM Circulation forming in which cold air will be forced to orographically rise while warming with terrain enhanced subsidence will occur over Powell Valley.

Doppler radar bright-banding, with a notable linear edge against the high country side, will develop if this occurs.

Rain, snow, sleet will all be possible in the transition zone.

By the way, these are the Appa-LATCH-ians not the Appa-LAY-ians as many say ( a disrespectful way to speak about these mountains in the view of many long-time residents and pioneer descendants ).

Based on weak-moderate TIM Circulation development, exclusively identified by Wayne Browning, I expect that a large gradient in snow depths to develop across southern and central portions of Wise County and northern portions of Scott-Lee counties (differences highlighted above are not as great as observed during the January 1998 and December 2009 storm events given this storm is not expected to be as strong as those systems).

It is nearly impossible for the floor of Powell Valley, southwest of the Valley Head, to accumulate significant snow on easterly (E-SE) flow streaming across the high country of the High Knob Massif.  So, if this type of flow develops I expect most of the accumulation toward Big Stone Gap to occur after low-level flow shifts more northerly in direction late Sunday.

Meanwhile, the 7 PM Friday NAM Model group is in and predicts 10″ to 13″ for the Wise gridpoint.

The 12 KM NAM should not be used for mesoscale forecasting, but it can be used for other purposes with the NAM group often being good in complex terrain once weaknesses are learned for any given location and compensated for by forecasters.

Here I am talking about highly detailed local forecasting amid complex terrain (above), as it is obvious by looking at this graphic the model is not accounting for local terrain variations.

A problem with the 3 KM NAM (below) by contrast, is that it tends to over-predict snow in orographic locations near the eastern Continental Divide and to under-predict snowfall in favored lifting zones (like the High Knob Massif) removed from this divide.

Increase the resolution to 3 KM; however, the model becomes much better ( below ).  Note it is predicting more than a foot of snow over Big Cherry Lake basin and the High Knob Massif and as little as 2″ in Powell Valley.  Although this will NOT capture the true, real life gradient it has the right idea versus the broad-brushed depiction shown by the 12 KM NAM.

The latest GFS-FV3 is supporting heavy-excessive snowfall with its 7:00 PM Friday run.

The latest GEM (Canadian) model run continues to predict heavy-excessive snowfall.

Model Runs And Saturday Thoughts

Model runs Saturday have all come in stronger with the storm system, illustrating that the Friday wobble was just that and the pattern is what must always be forecast.  Past such events have hammered the local mountains and there is no current indications to say this will not again happen; although, hopefully not to the extent of January 1998 and December 2009.

The GFS-FV3 is in test mode, being developed to replace the operational GFS package which has major problems related to its mathematical-physical parameterizations of many processes within its atmospheric boundaries.

The 7:00 AM run of the European Model increased its prediction to 14″ for the Wise gridpoint, in line with the NAM Model; although, some ensemble members were higher and some lower ( the 51-member mean was 11″ and well above their Friday forecast ).

The 7:00 PM Saturday NAM Model run is nearly identical to its 1:00 PM forecast, with 16″ to 22″ predicted at the Wise gridpoint.

Mountain Area Forecast ( Dec 3-5 )

Caution Is Advised For Slick Patches On Roadways, Especially Secondary Routes, into Thursday Morning

Former Alerts

Expect Widespread Sticking Snow Along and West to North of the High Knob Massif and Tennessee Valley Divide Into Wednesday AM

ALERT For Accumulating Snowfall Monday Night Into Tuesday Morning and during Tuesday Night Into Mid-Morning Wednesday

Great Lake connected NW Flow snow showers & flurries will develop by Monday night into Tuesday morning along and NW-N of the High Knob Massif-Tennessee Valley Divide.

Showers of sleet, locally heavy, have also been added to the forecast ( especially at low-middle elevations Monday night ).

Slippery road conditions will be possible during these time periods, especially on secondary roads.  Low cloud bases are expected to produce a prolonged period of rime formation at  upper elevations in the High Knob Massif ( on trees ).

An upper air disturbance and NW-WNW flow will cause snow during Tuesday night into mid-morning Wednesday with somewhat deeper moisture and colder air aloft.  Due to cold air aloft, local snow squalls (snow bursts) will remain possible into the afternoon.  

**NOTE: Travelers should use caution at highest elevations in the High Knob Massif along Routes 237, 238, State Route 619 and other Forest Service roads due to lingering limbs and cut trees along roadways in wake of the major ice storm of November 15 as documented and forecast at 111118 Forecast.

Overnight Into Monday Morning

Mostly clear and windy, then becoming partly to mostly cloudy.  Winds SW-W at 10-20 mph, with higher gusts, on mid-upper elevation mountain ridges & exposed plateaus.  Temperatures widespread in the 40s to lower 50s.  Wind chills in the 30s & 40s ( coolest upper elevations ).

Monday Afternoon

Becoming cloudy & turning colder.  Lowering cloud bases by late.  Winds shifting WNW-NW at 5-15 mph with higher gusts.  Temperatures falling through the 40s at low-mid elevations and through the 30s upper elevations ( to around freezing highest elevations ).

Monday Night Into Mid-Morning Tuesday

Snow showers and flurries developing, with showers of sleet during the evening (especially at lower-mid elevations).  Winds NW at 5-15 mph with higher gusts.  Temperatures dropping into the lower 30s to the lower 20s ( coldest at highest elevations ).  Wind chill factors in the 10s & 20s, except single digits in gusts highest peaks.  Riming on trees at upper elevations.

Tuesday Afternoon

Mostly cloudy & cold.  Chance of flurries and snow showers.  NW winds 5-10 mph with some higher gusts.  Temperatures varying from 20s in upper elevations to the low-mid 30s at low-mid elevations along & NW-N of the High Knob Massif-Tennessee Valley Divide.  Wind chills in the 10s & 20s.  Riming on trees at highest elevations.

Tuesday Night Into Mid-Morning Wednesday

Light snow, snow showers & flurries.  Bursts of locally heavy snowfall.  Winds NNW-WNW at 5-10 mph, with higher gusts.  Temperatures varying from mid-upper 10s to the upper 20s ( coldest at highest elevations ).  Wind chills in single digits & 10s to lower 20s ( coldest highest elevations ). Riming at upper elevations.

Wednesday Afternoon

Snow showers & flurries.  Bursts of locally heavy snow possible, especially during early-mid afternoon.  WNW to NW winds 5-15 mph with higher gusts.  Temps in the 10s to lower 20s upper elevations to the 20s to around 30 degrees low-mid elevations.  Wind chills in the 10s and single digits (coldest high elevations).

 

Updated Forecast:

*Snowfall Forecast Monday Night Into Wednesday

General 1″ to 3″ with locally higher amounts for locations along and north-west of the High Knob Massif and Tennessee Valley Divide.

No sticking up to locally 1″ in downslope locations.

*Another period of accumulating snow is expected during Thursday night into Friday morning.

*The potential for major winter storm development is being monitored for the December 9-11 period.  Odds are now increasing for a crippling snow event in the southern Appalachians.  Stay tuned for later updates on timing, amounts, and placement of heaviest snow.

 

Weather Discussion ( Short-Term )

Widespread light snow accumulations, at elevations above 2000 feet, were observed into morning hours of Tuesday within locations along and west-north of the High Knob Massif and Tennessee Valley Divide on NW upslope flow.

A upper air wave and pocket of cold air aloft will combine with a continuation of NW-W flow to caused widespread snow accumulations at all elevations along and north to west of the High Knob Massif & Tennessee Valley Divide during Tuesday night into Wednesday.

Wednesday was a wintry day across the mountain area with widespread 1″ to 4″+ snow accumulations during this event  ( 4″ in Clintwood and 2″ to 4″+ snow depths across the Wise-Norton and High Knob Massif area ).

Crippling Snowfall Potential

Looking ahead a crippling snowfall potential is being monitored for the December 9-10 period, but specific details will have to wait until this system comes into view of short-range terrain models.

The current ensemble mean for the 21-members of the GFS Model is similar to the 51-member mean of what is often the superior European Model (although, the GFS tends to better define the High Knob Massif ).

*I am not allowed to show the European Model information without a very expensive license to legally display its more detailed forecast graphics.

The Wednesday range of the 51-Ensemble Members of the European Model had predicted snowfall totals for the December 8-10 event varying from less than 2″ to more than 24″ at the Wise gridpoint, but the MEAN between all ensembles and the operational run was firmly within the 12″ to 18″ range.

There is likely to be a huge snow depth variation across the area, with not only snow amounts but the density of snowfall being critical factors to impacts.

Locations severely impacted by the January 1998 and December 2009 storm events initially look to be at the greatest risk once again from this storm.  Stay tuned for later updates as details become defined.

Weather Headlines ( Dec 1-9 )

ALERT For Strong Southerly Winds Saturday Afternoon & Evening With 20-40+ MPH Gusts  (Especially At Mid-Upper Elevations)

Residents and travelers at mid-upper elevations should use caution and be alert for the possibility of breaking-falling tree limbs, etc…given wet soil conditions and strong gusts.

Strong winds are generating an array of orographic cloud forms across the High Knob Massif area, with both standing waves and other types ( like lenticular ) being observed.

I first highlighted the possible need for an alert in my headlines for the 113018 Forecast period.

*A wintry pattern returns next week with cold air and several possible snow and rime producing waves.

The first period of interest for snow and cold being during December 4-7, with orographic upslope flow enhancement on NW-N flow.  Rime formation is now expected to begin in the High Knob Massif, at upper elevations, by later on Monday ( December 3 ).

*The potential for major winter storm development is being monitored for the December 8-9 period.  A more widespread regional impact exists during this time.