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.
