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.
Slick Roads On The Wise Plateau – Friday Afternoon – Professor Wally Smith
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.
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.
Stream Level Up to 6.3 Feet ( 0.2 feet below flood stage ) At 3:15 PM
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 ).
Snow Accumulation On Eagle Knob At 11:43 AM Friday
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 Just Beginning To Fall At UVA-Wise At 11:43 AM Friday
Snow began falling at UVA-Wise around 11:30 AM.
Heavy Snow Makes Roadways Slick In Wise During Early Afternoon Friday
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 In High Chaparral
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 ).
Snow Covered Roads In High Chaparral At 4:30 PM Friday
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 ).
Eagle Knob of High Knob Massif At Sunset Friday ( Around 8″ of snow )
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.
European 51-Member Ensemble Mean 500 MB Height Anomalies: Days 0-4
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.
European 51-Member Ensemble Mean 500 MB Height Anomalies: Days 6-10
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 ).
Mean Temperature At 90 Degrees North Latitude and 10 MB
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.
European Model Atmospheric Analysis At 7 AM December 21, 2018
Note the changes at 60 N and 10 MB in 10 days.
European Model Atmospheric Forecast At 7 AM December 31, 2018
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.
*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.
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.
Low Clouds Dominated The Mountain Landscape Sunday_UVA-Wise
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.
Strong Rises On Streams ( Steep Creeks ) DrainingThe 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.
Mountain Wave Winds Develop Along Pine Mountain
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.
Mountain Waves & A Standing Wave Visible Along High Knob Massif
The standing waves will remain for hours, even though they may not always be visible as condensation moisture ( other clouds ) obscures them.
Eagle Knob of High Knob Massif – Dense Fog and Strong SE-SSE Winds
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.
European Model 51-Member 500 MB Ensemble Mean Anomalies
ALERT For A Continuation Of Hazardous Road Conditions – Especially Secondary Routes Into Tuesday
Secondary roads remain snow covered and locally impassible, with more time being needed for VDOT work to be completed on these roadways.
ALERT For ALL Roads Tonight-Tuesday Morning With Refreezing And Black Ice
A sharp temperature drop tonight into Tuesday morning will create icy patches with refreezing.
Air temperatures are expected to plunge into single digits and 10s, except locally colder in high mountain valleys at upper elevations where dry advection will be occurring to enhance cold air drainage over deep snow cover.
To see larger images, and a short time-lapse of the storm, reference the High Knob Landform and scroll down to the Major Winter Storm section.
Orographic Snow Clouds Capping High Knob Massif – December 10, 2018
Majestic orographic snow clouds capped the high country for both many miles and hours Monday morning, laying across heads of the Big Cherry Lake to High Knob Lake corridor ( as seen above ). This was adding even more moisture to trees.
Storm snowfall totals ended up as expected within the lifting zones of the High Knob Massif where a general 1 to 2 feet of snow accumulated.
Totals varied from around a foot in Wise to 19″ at High Chaparral ( 3300 feet elevation ) to 2 feet or more in the main crest zone of the massif.
This included the Scott County side where air was rising up toward the High Knob Massif, with a foot or more of snow reported from Natural Tunnel State Park and Duffield to Castlewood & Abingdon downstream of the massif.
Eagle Knob of High Knob Massif – Orographic Clouds At 10:44 AM (Dec 10)Orographic Snow Clouds Viewed From UVA-Wise
One of the most dramatic short-distance contrasts observed anywhere with this storm occurred as air flowed across the High Knob Massif and through an orographic standing wave to subside and warm amid lee-ward ( downslope ) locales from Powell Valley to Big Stone Gap and Pennington Gap.
GOES-16 Visible Image – High Knob Massif Snow Shadow
Air flow trajectories in the 900 to 600 mb layer were streaming across Scott County and through the wave standing along the High Knob Massif.
NAM Model Analyzed 850 MB Streamline Flow At 1:00 PM Sunday (Dec 9)
Snowfall was enhanced on the rising air side and diminished along and downstream of the subsidence, or sinking, air side of the massif.
This event, and many past storm events, revealed a transition zone of mixed precipitation that became orographically anchored along the lee-ward side where warmer air was being forced to sink as colder air ( on the rising side ) was being lifted upward over the high country ( a Thermally Indirect Circulation ).
This is more than just a mountain-valley phenomenon as this and many past events demonstrate, with significantly less snow depth & total precipitation at high elevations in adjacent Black Mountain.
*More than 2.00″ of water equivalent in the High Knob Massif during this event was 1.00″ or more above what was reported on Black Mountain.
NAM Model Analyzed 700 MB Streamline Flow At 1:00 PM Sunday (Dec 9)
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.
High Knob Massif Webcam – University Of Virginia’s College At Wise
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.
NAM 12 KM Model Run At 7:00 AM Friday
NAM 12 KM Model Run At 1:00 PM Friday
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).
NAM 12 KM Model Run At 1:00 PM Friday – December 7, 2018
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 ).
Canadian (GEM) Model Run At 7:00 AM Friday – December 7, 2018
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.
Updated Storm Snowfall Forecast – Made December 8, 2018
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).
850 MB Moisture and Streamline Forecast At 7:00 AM Sunday 925 MB Moisture and Streamline Forecast At 7:00 AM Sunday
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.
NAM 12 KM Model Run At 7:00 PM Friday – December 7, 2018
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.
NAM 3 KM Model Run At 7:00 PM Friday – December 7, 2018
The latest GFS-FV3 is supporting heavy-excessive snowfall with its 7:00 PM Friday run.
GFS-FV3 Model Run 7:00 PM Friday – Total 66h Precipitation
The latest GEM (Canadian) model run continues to predict heavy-excessive snowfall.
GEM Model Run At 7:00 PM Friday – December 7, 2018
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.
NAM 12 KM Model Run At 7 AM Saturday – December 8, 2018NAM 12 KM Model Run At 1:00 PM Saturday – December 8, 2018NAM 3 KM Model Run At 7:00 AM Saturday – December 8, 2018NAM 3 KM Model Run At 1:00 PM Saturday – December 8, 2018Canadian GEM Model Run At 7:00 AM Saturday – December 8, 2018GFS-FV3 Model Run At 7:00 AM Saturday – Total Precipitation
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.
GFS-FV3 Model Run At 1:00 PM Saturday – Total Precipitation
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 ).
NAM 12 KM Model Run At 7:00 PM Saturday – December 8, 2018
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.
NAM 3 KM Model Run At 7:00 PM Saturday – December 8, 2018
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.
High Knob Massif Webcam – University Of Virginia’s College At Wise
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.
High Knob Massif Webcam – University Of Virginia’s College At Wise
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.
GFS 21-Member Ensemble Mean Total Snowfall Forecast
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.
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.
High Knob Massif Webcam – University Of Virginia’s College At Wise
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.
Black Mountain Mesonet
I first highlighted the possible need for an alert in my headlines for the 113018 Forecast period.
Lonesome Pine Airport In Wise
*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.
ALERT For Dense Fog At Mid-Upper Elevations Along And SW of the High Knob Massif-Tennessee Valley Divide ( This Includes The Town of Wise )
High Knob Massif Webcam – University Of Virginia’s College At Wise
Now that the low-level jet streak has passed ( which was only predicted here ) the ALERT is now changed to one for low clouds bases ( Dense Fog ) with SW upslope flow.
Lonesome Pine Airport
Travelers should use extreme caution along U.S. 23 through the head of Powell Valley where this type of flow can often generate some of the most dense fog.
Former Alert
ALERT For A Period Of Strong SSW to WSW Winds Developing Into Friday Morning — Especially At The Middle-Upper Elevations
A low-level jet streak near the 850 MB level will move over the mountains into Friday morning. Wind gusts of 20-40+ mph will develop at mid-upper elevations, with local gusts over 50 mph being possible on the highest peaks.
*Rain showers will continue overnight into morning hours of Friday, becoming increasingly wind driven and locally heavy. Downpours will be most likely with strong SW upslope flow into the High Knob Massif and Tennessee Valley Divide.
Expect the high country to be engulfed in clouds, with fog drip from trees adding to rainfall, throughout Friday into Saturday morning across the High Knob Massif.
*A wet pattern will continue into early Sunday with another round of strong winds. Another ALERT may be needed on Saturday.
Another prolonged period in the clouds, with fog drip from trees, will develop later Saturday into Sunday at the upper elevations in the High Knob Massif.
*A wintry pattern develops next week. Systems with possible accumulating snow are being monitored for the December 4-6 and December 8-9 periods. Stay tuned for later timing updates.
ALERT Continues For Hazardous Conditions Into Wednesday Morning With Unseasonable Cold and Slick Roads ( Patchy snow on main roads, widespread snow on secondary roads )
Former Alert
ALERT For Hazardous Road Conditions Late Monday Into Tuesday Morning, Especially On Secondary Roads At Middle To Upper Elevations
Much colder air will pour into the mountain area Monday afternoon into Tuesday, with bitter wind chills and a prolonged period of below freezing air temperatures expected ( Monday into Thursday ) at middle to upper elevations.
Rain showers will change to snow showers-flurries Monday afternoon, with accumulating snow levels dropping from upper elevations into middle-lower elevations by late Monday into Monday night.
*A Snow Squall potential will exist by later Tuesday into Tuesday evening, with bursts of intense snow becoming possible. An alert for hazardous travel conditions may be needed.
*A prolonged rime formation event is expected at upper elevations across the High Knob Massif starting Monday afternoon and extending into the predawn to morning hours of Wednesday ( November 28 ).
*Strong & gusty SW-WSW winds are expected at mid-upper elevations late Thursday into Friday as milder air pushes into the mountain area ( sensible warming will be offset by increased wind chills ).
Mountain Area Forecast Details
Overnight Into Monday Morning
Windy with rain showers. A period of downpours possible. Winds S-SW at 10-20 mph, with higher gusts, at elevations below 3000 feet. S-SW winds 15-30 mph, with higher gusts, on mountain ridges above 3000 feet. Widespread temps in the 40s, with 30s at high elevations toward morning. Dense fog ( orographic clouds ) at upper elevations. Wind chills dropping into the 20s & 30s ( coldest highest elevations ) into morning. Light winds in sheltered valleys will give way to strong wind gusts into morning.
Mid-Morning Monday Through The Afternoon
Windy. Turning much colder. Rain showers changing to snow showers & flurries. Low clouds. Riming developing at upper elevations. Winds WSW to WNW at 10-25 mph, with higher gusts. Temperatures falling through the 30s at low-middle elevations and through the 20s at upper elevations. Wind chills dropping into the 20s & 10s, except single digits to near 0 degrees at high elevations by late.
Monday Night Into Tuesday Morning
Snow showers & flurries. Windy & unseasonably cold. Winds W-NW at 5-15 mph, with higher gusts, below 2700 feet. W-NW winds 10-20 mph, with higher gusts, above 2700 feet. Temperatures dropping into the mid 10s to the middle 20s ( coldest at highest elevations ). Wind chills in 10s, except single digits above and below zero at the upper elevations. Riming at upper elevations.
Tuesday Afternoon-Evening
Cloudy with a chance of snow showers-flurries. Local snow squalls becoming possible ( bursts of intense snow ). Winds W-WNW at 10-20 mph, with higher gusts. Temperatures in the 20s to near 30 degrees at lower-middle elevations along and north of the High Knob Massif-Tennessee Valley Divide and in the 10s to lower 20s at upper elevations. Wind chills in the 10s to lower 20s, except single digits to low 10s at the upper elevations. Riming at high elevations.
Overnight Into Wednesday Morning
Snow showers-flurries and light snow. Unseasonably cold. WNW-NW winds 5-15 mph with some higher gusts. Temps varying from single digits at high elevations to the 10s to near 20 degrees. Wind chills in single digits to low 10s at lower-middle elevations and 0 to -15 below zero at upper elevations ( coldest in gusts at highest elevations ).
Mid-Morning Wednesday Through The Afternoon
Flurries ending. Becoming partly to mostly sunny. Cold. Some increase in high clouds possible by late. W to WNW winds at 5-10 mph with some higher gusts. Temperatures varying from lower 20s to the lower 30s ( coldest at the highest elevations ). Wind chills varying from the 20s at low-middle elevations to the 10s ( single digits in gusts on highest peaks ).
*Seasonally cold weather will dominate conditions during Thanksgiving Week across the mountains.
*Rain showers Monday night will give way to snow showers & flurries into Tuesday as air turns colder.
*Although only light snow amounts are expected, I do expect sticking at high elevations and another period with significant rime formation Tuesday (via moisture capture by trees) into early Wednesday within upper elevations, above 3000 feet, in the High Knob Massif.
Rime Covered Northern Slopes of High Knob Massif – November 14, 2018
*The potential for major storm development is being monitored for the final days of November into early December. Stay tuned for later updates.
Mountain Area Forecast ( Nov 18-21 )
Sunday Night Into Monday Morning
Partly-mostly cloudy (mid-high clouds). SSW-WSW winds at 5-15 mph along mid-upper elevation mountain ridges. Temperatures varying from lower 30s to the lower 40s, except locally colder within sheltered mountain valleys. Wind chills generally in the 30s, except 20s in gusts on highest peaks.
Monday Afternoon
Increasing and lowering clouds with a chance of rain showers, especially by late. Winds S-SW at 10-20 mph with higher gusts ( winds may gust over 30 mph along the higher mountain ridges ). Temperatures varying from 40s in upper elevations to the mid-upper 50s in downslope locations of northern Wise and Dickenson counties. Wind chills in the 30s to lower 40s at higher elevations.
Monday Night Into Tuesday Morning
Rain showers developing. Turning colder. Rain showers will change to snow showers at high elevations by morning. Winds SSW-SW at 5-15 mph, with higher gusts on mountain ridges and plateaus below 2700 feet. Winds SW-W at 10-20 mph, with higher gusts, on mountain ridges above 2700 ft. Winds shifting WNW-NW by morning. Clouds lowering to obscure higher mountain ridges. Temperatures falling into the 30s to around 40 degrees, except to around 30 degrees on highest peaks, by morning. Wind chills in the 20s & 30s, except dropping into 10s on high peaks by morning.
Tuesday Morning Through The Afternoon
Low clouds & cold. A chance of drizzle, flurries, and snow showers. Orographic clouds with dense fog-riming at high elevations. Winds WNW-NW at 5-15 mph with some higher gusts. Temperatures nearly steady to slowly falling in the 30s at lower-middle elevations along and west to north of the High Knob Massif-Tennessee Valley Divide, and into 20s at upper elevations. Wind chill factors in 20s to around 30 degrees, except 10s to lower 20s at high elevations.
Tuesday Night Into Wednesday Morning
Mostly cloudy & cold. Winds W-WNW at 5-15 mph, with higher gusts, on mid-upper elevation mountain ridges. Riming continuing at high elevations. Temps dropping into the 20s to around 30 degrees, except around 20 F at high elevations. Wind chills in the 10s & 20s along mid-upper elevation mountain ridges, with single digits on highest mountain ridges and peaks.
Holiday Season Discussion
This week marks the official beginning of the holiday season, with a passing early week front expected to turn conditions colder prior to Thanksgiving day…but nothing like appears to be upcoming to close out November 2018.
Looking From High Country of Rime Covered Big Cherry Lake Basin
This chilly trend shows up on the 5-day mean charts from the European Model and its 51-member ensemble group; although, some moderation follows briefly the extended trend is looking to turn sharply colder.
European 51-Member Ensemble Mean 500 MB Height Anomalies: Days 1-5
November 20-22 will be the coolest days in this period, especially Tuesday into Wednesday ( November 20-21 ), leading up to Thanksgiving day.
Brief moderation is then looking to be followed by an active pattern which turns sharply colder during the final days of November into early December ( to emphasize this again ).
European Model 850 MB Temperature Anomalies Forecast: Days 1-5
Some late week-weekend moderation is currently expected ahead of what looks to be an interesting period to finish out November and open December 2018 ( are you beginning to sense that I am trying to shift your focus toward the week after Thanksgiving ).
European 51-Member Ensemble Mean 500 MB Height Anomalies: Days 6-10
Ridging across Greenland is expected to aid increasingly negative AO and NAO teleconnections, which with a trend toward an increasingly +PNA after November 24 will act to bring wintry conditions into the mountain region. If the EPO also trends negative, as currently suggested, that will up the ante for some serious winter weather.
