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.
