Mountain Area Forecast ( Feb 14-17 )
ALERT For A Continuation Of Strong SW Winds At Mid-Upper Elevations During Thursday Night Into Friday, With Increasing Gusts Into Lower Elevations During The Overnight-Predawn Of Friday
A strong SW flow of air will continue in advance of an approaching cold front through Thursday Night into the morning hours of Friday before a wind shift to W then N directions occurs during the day Friday. Local power outages will remain possible.
The leading edge of this front may be marked by a line of heavy rainfall, followed by widespread rainfall of lesser intensity. Remain alert for possible water level rises.
An ALERT For DENSE Fog Is Likely For Late Friday Into Friday Night With Dropping Cloud Bases On Northerly Upslope Flow Along & North Of The High Knob Massif And Tennessee Valley Divide ( A Limited Period )
Hydrology ALERT For Significant Rainfall Amounts
A moist low-level air mass will combine with strong SW winds to produce rain showers at times through coming days. Downpours will be possible, especially within the upslope corridor along and southwest of the High Knob Massif & Tennessee Valley Divide.
A large region with significant rainfall will be possible during the next 5-7 days, with heaviest amounts expected to again fall along and west of the Appalachians from the mountains to Ohio River.
Due to saturated conditions in wake of recent flooding persons living along streams and in low-lying, flood prone locations will need to remain alert for the possibility of water level rises.
ALERT For Dense Fog Across Mid-Upper Elevations And Within The SW Flow Funneling Zone Along U.S. 23 At Powell Valley Overlook
Dense fog was present throughout the daylight hours of Wednesday along the flanks of the High Knob Massif and highest elevations, as well as within the Head of Powell Valley where SW flow rises to funnel through Little Stone Mountain Gap ( on either side of Powell Valley Overlook ).
This has been causing a sudden reduction is visibility along U.S. 23 such that caution is advised for those traveling between the Town of Big Stone Gap and City of Norton.
Overnight Into Wednesday Morning
Cloudy and windy. Rain developing with a chance of downpours. Low clouds with widespread dense fog at upper elevations. SSW to SW winds 10-25 mph, with higher gusts. Temperatures widespread in the 40s to around 50 degrees.
Wednesday Morning Through The Afternoon
A chance of rain showers. Local downpours possible. Low clouds with dense fog at high elevations. SSW-SW winds 10-20 mph with higher gusts. Temperatures in the upper 40s to middle 50s.
Wednesday Night Into Thursday Morning
Rain showers. Downpours possible. Low clouds with dense fog at mid to upper elevations. SW winds 10-20 mph, with higher gusts, on mountain ridges-plateaus below 2700 feet. SW-WSW winds 15-25 mph, with higher gusts, on mountain ridges above 2700 feet. Unseasonably mild with temperatures mainly in the 50s.
Thursday Morning Through The Afternoon
A chance of rain showers. Downpours possible. Low clouds with dense fog at upper elevations and in SW upslope flow sites at mid elevations ( e.g., Powell Valley Overlook ). SSW-SW winds 15-25 mph, with higher gusts. Unseasonably mild with temperatures from the low 50s to the low 60s.
Overnight Into Friday Morning
Mostly cloudy. Windy. Unseasonably Warm. Chance of showers developing toward morning. SW Winds 15-30 mph, with higher gusts. Temperatures in the 50s to lower 60s.
Friday Morning Through The Afternoon
Morning rain, heavy at times. Windy. Turning colder with rain tapering to showers or a mix. Rain changing to snow at the upper elevations by mid-late afternoon before ending, or becoming flurries. Morning temperatures in the 50s to lower 60s dropping sharply during mid-late afternoon into the lower 30s to lower 40s ( coldest highest elevations ). A drop in cloud bases with dense fog formation for a period during late afternoon-early evening at elevations above 2500-3000 feet. Developing mid-later afternoon wind chills in the 20s & 30s.
Friday Night Into Saturday Morning
Low clouds & fog giving way to mostly cloudy skies. Areas of dense fog possible at low elevations. Winds becoming light & variable. Temperatures varying from low 20s to lower 30s ( coldest in upper elevations ).
*Another wave of rain, with locally heavy amounts, is expected to overspread the area during Saturday. This could cause strong rises on creeks.
Reference Late Winter In The High Knob Massif for more details.
The currently forecast upper air pattern into next week continues to look most favorable for another high water event, with deep tropical moisture set to generate additional heavy to excessive rainfall. See my updated discussion below for more details.
Weather Discussion ( Wet Pattern )
Thursday Night ( Feb 15 ) Update
A couple more rain producing systems will be crossing the mountain area into this weekend, with strong SW winds in advance of the first system into Friday morning.
A general 1.00″ to 2.00″ of rain will be possible with these two waves ( heaviest amounts centered on the morning to early afternoon hours of Friday and again Saturday afternoon-early Saturday evening ).
Due to orographic clouds capping high elevations, and moderate to strong lift, locally higher rain amounts will be possible. What do I mean by orographic clouds?
Once higher level clouds dissipated the orographic capping clouds became visible. Note how the cloud bank stretched across the High Knob Massif ( above ) is stationary over time ( below ), indicating that it is being supported by orographic lifting on strong SW flow ( in this case ).
This is part of an important seeder-feeder precipitation process in which rain falling out of a higher altitude seeder cloud falls down through the moisture rich environment of the feeder cloud and becomes enhanced, with more rainfall subsequently reaching the surface than falls out of the seeder clouds ( and more than is able to be detected by Doppler radar whose beam shoots over top the orographic feeder clouds capping the high country ).
This is part of the reason why rainfall is always under-estimated for the High Knob Massif area, with my climatology showing that this process is important throughout the year but especially in the orographic forcing season ( November-April ) when strong winds generate long-lived orographic cloud masses.
People living along streams, and in low-lying poor drainage locations, will need to remain alert for water level rises into Friday afternoon and again later Saturday into Saturday night. Given general 5.00″ to 10.00″+ amounts already observed this month, it will not take as much rain to generate water level rises.
As noted above, I continue to think next week will offer a more serious threat to the mountain region with more heavy to excessive rainfall becoming likely.
Although specific rainfall forecasts vary from run to run and among models, and no single model run should be taken as being accurate ( like above ), composite ensemble means for the European Model group and GFS are again showing a strong signal for heavy to excessive rainfall amounts.
A western Atlantic High, analogous to a summer-like Bermuda High, in combination with a deep upper air trough anchored by Gulf of Alaska ridging is truly an ominous signal for heavy-excessive rainfall from the mountains west to the Mississippi River.