Mountain Area Forecast ( Dec 18-20 )

Dense Freezing Fog Will Now Be The Main Factor Into Monday For Locations At Middle To Upper Elevations Along & North Of The High Knob Massif & Tennessee Valley Divide ( Above 2000-2500 Feet In Elevation )

*Visibility near zero at times, within this orographically generated upslope cloud deck of freezing fog, is expected.  Caution Is Advised.

An ALERT Continues For Strong Winds At Middle To Upper Elevations Into Sunday.  Wind Gusts Of 30-50+ MPH Will Continue Into The Predawn-Sunrise Period.

ALERT For Icing From Mid-Morning To Afternoon Hours On Sunday With Freezing Rain And Sleet In Addition To A Flash Freeze Up In Counties Along Either Side Of The Virginia-Kentucky Border.

**Vertical temperature profiles and wind fields indicate that a change to freezing rain then to sleet will be more likely than snow given that SW-WSW flow continues aloft in the 825-725 MB layer.  

This keeps an above freezing layer aloft which will change snow falling aloft into rain that will initially freeze, before changing into sleet as the cold air deepens in the vertical above the surface.  In addition, any wetness lingering from heavy morning rain will tend to freeze on porches, decks, and other surfaces amid a rapid temperature drop between mid-morning and early afternoon.

 With LUCK the bulk of precipitation will push east before temps drop below freezing; however, freezing fog, drizzle and a general freeze up remain likely.  Therefore I feel that an ALERT is the right call for everyone to become aware of these threats ( as it takes only a bit of icing to cause problems ).

Overnight Into Sunday Morning

Showers with a chance for thunderstorms.  Locally heavy rainfall.  ROARING Winds.  SSW-SW winds 15-25 mph, with higher gusts, along mountain ridges-plateaus below 2700 feet.  Winds SSW-SW 20-35 mph with higher gusts along upper elevation mountain ridges.  Mild with temperatures steady or rising into the 50s to near 60 degrees.

Sunday Mid-Morning Into Sunday Afternoon

Rain mixing with and changing to freezing rain & sleet.  A period of snow possible.  Windy.  Turning sharply colder.  Low cloud bases-freezing fog at upper elevations dropping into mid elevations late.  SW winds shifting NW to N at 5-15 mph, with higher gusts.  Temps falling into the 30s and 20s, except into the upper 10s at highest elevations by late.  Wind chills dropping into 10s & 20s, except single digits at highest elevations by late.

Sunday Night Into Monday Mid-Morning

Low clouds with dense freezing fog across middle to upper elevations.  Chance for light snow, sleet or freezing drizzle.  Winds N-NE at 5-15 mph, with higher gusts.  Temperatures dropping into the mid 10s to mid 20s ( coldest at highest elevations ).  Winds chills in the single digits & 10s, except around or below 0 degrees in gusts on highest peaks.

Monday Mid-Morning Through Monday Afternoon

Cloudy to mostly cloudy below 3600 feet.  Partly to mostly sunny above 3600 feet.  Cold.  Winds N-NE at mostly less than 10 mph.  Temperatures varying from mid 20s to low 30s ( upper 20s to around 30 degrees Norton-Wise ).

Monday Night Into Tuesday Morning

Low clouds below 3600 feet in the evening, then low clouds mainly below 3000 feet by morning.  Partly cloudy above.  Cold.  Winds Light & variable with vertical elevation.  The temperatures varying in the 20s beneath clouds.  Temps rising to around or above freezing along upper elevation mountain ridges above 3300-3500 feet.

 

Weather Discussion ( Nasty Mess )

Monday Morning Update

I have updated my forecast for today to account for epic conditions in the vertical due to a strong inversion that I have highlighted now for a couple days.

Elevations below 3600 feet this morning are beneath a layer of clouds which marks the inversion, while conditions are mostly sunny ( with some high clouds ) above that level.

If vertical mixing increases enough it could mix out the low clouds into middle elevations ( with sunshine ) later today; however, it is likely that lower elevations will remain under the cloud deck.  Middle elevations also have a good chance of staying under the deck.  If so, then it will be a raw, cold day for those places within middle-lower elevations.

Right now, conditions are simply epic with at least a portion of the heavily rimed crest zone of the High Knob Massif like an island above a sea of clouds ( Black Mountain’s summit and the twin Beartown’s are also above the deck ).

 

Sunday Afternoon Update

The main focus now will be on freezing fog and a continued drop in temperatures tonight into Monday morning.  Light frozen forms of precipitation may continue to fall at times, with a warm layer aloft generating a strong inversion that will trap clouds well into Monday.

This is an orographically forced or generated fog so visibility will at times be near zero.  Extreme Caution is advised given that it is also a freezing fog with riming.

While Winter Wonderland Conditions will be developing into Monday, it will take a while before all the terrain will again become visible given this cloud trapping inversion aloft ( the same warm layer which kept snow flakes at a minimum, with freezing rain and sleet being the primary forms reported Sunday ).

Meanwhile, SLOW DOWN and Be Safe…Checking For Ice On Porches, Decks, Walks, Roads And Anything  You Need To Be Walking-Traveling On Outside.

 

Mid-Day Sunday Update

I have updated my forecast to allow for some snow mixing in or a period of light snow.  Temperatures have dropped into the upper 20s on High Knob as of 11:30 AM with some flakes of snow mixing with freezing rain-sleet.

Prior to freeze up the event total precipitation reached 1.84″ on Eagle Knob of the High Knob Massif.  That means more than 2.00″ given tremendous overnight winds = a lowered rain gauge catch.  

Peak wind gusts around 50 MPH were recorded in Wise, where sustained speeds as high as 35 MPH occurred.  Peak wind gusts of 50-70+ MPH were common at higher elevations.

Sleet is now the main precipitation type in Clintwood, so all forms of frozen will be possible into this afternoon.

While the bulk of precipitation will be moving east of the area, the main concern continues to be icing from temps dropping below freezing into this afternoon along with lowering clouds bases and formation of freezing fog at middle-upper elevations along and north to northwest of the High Knob Massif and Tennessee Valley Divide.  Light frozen forms of precipitation will continue to be possible.

 

Previous Discussion

Reference My 121716 Forecast Discussion For More Details.

For those who love snow I have bad news, especially if model forecast soundings in the vertical are on target.

Winter Wonderland Conditions are; however, likely to develop with freezing rain, sleet, freezing fog and, just perhaps, freezing drizzle all occurring.  This will be the most pronounced for those living in middle to upper elevations ( above 2000-2500 feet ), but all of this area should remain alert to these threats.

Models tend to handle temperatures aloft better than within the more complex realm of the planetary boundary layer; thus, more confidence can generally be put into forecast temperatures above the DIRECT frictional influence of terrain features.  They can still be in error, of course, if anything can lift the air enough to erase the warm layer ( in this case ).  A SW-WSW flow aloft is however a notorious set up for frozen forms at the surface other than snow.

The problem is the 825 to 725 mb layer, seen on these soundings by the RED TEMPERATURE LINE that crosses to the right ( above 32 F ) side of the dashed blue line which rises on an angle upward from the 0 ( 0 degree Celsius or 32 Fahrenheit point ) at the bottom.

Observe that occurs above the PBL ( boundary layer ) where low-level winds shift SW-WSW, as indicated by the wind barbs along the right side ( right of the RED-GREEN lines ).  So the model says that warmer air will continue to be transported aloft over cold air transport ( advection ) in low-levels.  That = A MESS.  The only good news being that heaviest precipitation should be east of the area by the time elevations below 3000 feet drop below freezing.

Arctic air will simply surge into the western slopes of the mountains Sunday but a lingering warm layer aloft, above the mountains, will cause snow falling aloft to melt into rain that first freezes below on surfaces near the ground before changing into sleet ( sleet will develop at low-mid elevations, especially, as cold air deepens vertically ).

It appears that the greatest potential for freezing rain and sleet of significance will be from the elevation of Wise upward; however, as many may understand from experience it takes only a little ice to cause problems.  So even if the bulk of precipitation is to the east there remains an icing threat from multiple factors.

Locations along and north to northwest of the High Knob Massif-Tennessee Valley Divide will also be at highest risk given that the terrain will tend to block and slow the incoming arctic air ( delaying it enough to help reduce the risk for locations lee of the front range into river valleys of the Clinch & Holston ).

*If the Virginia side of the border gets lucky ( the KY side being unlucky ) then maybe Black & Pine mountains might be able to slow down the cold air transport enough to allow most of the precipitation to push east.  Locations around and above 3000 feet; however, remain likely in this case to  have temperatures go below freezing before rain ends.  An abundance of lingering low-level moisture will support the formation of freezing fog at elevations above 2000-2500 ft, and freezing drizzle-sleet for all elevations, along & north to northwest of the High Knob Massif-TN Valley Divide from late Sunday into Monday ( so icy conditions to some extent look to be upcoming for most places in this area ).

Meanwhile, ROARING winds continue to be the story at mid to upper elevations along the Cumberland Mountains ahead of an approaching squall line and band of rain west of the Appalachians in Kentucky & Tennessee.

Many gusts over 50 mph ( to around 60 mph ) have been recorded at 2774 feet on Pine Mountain.  No forecasters should doubt that the high country above 3000 to over 4200 feet is not being blasted by this powerful SW flow which climatologically is the most windy and the most common trajectory in the Cumberland Mountains.

Winds are BLASTING the summit of the High Knob Massif with everything rockin’ tonight.  That was, of course, in my forecast and is no wonder given the potent SW wind field over top of the region ( below ).  It should not ever be forgot that hundreds of people live above 3000 feet in the massif, so it is not just trees and the mountain being blasted!

A total of 0.25″ to 0.50″+ ( 0.44″ highest rain gauge report but with significant undercatch in high winds ) has fallen so far across the High Knob Massif, with heavy rains and embedded thunderstorms likely by the predawn of Sunday.

Additional heavy precipitation amounts are likely into Sunday, especially as the strong SW winds help enhance amounts into lifting zones of the High Knob Massif and Black-Pine mountains.

The Storm Prediction Center maintains a marginal risk for severe thunderstorms up to the Virginia-Kentucky border, with the primary risk being wind damage.

Stay tuned to NOAA Weather Radio and your favorite media sources for possible watches-warnings and any other advisories that might be needed.

Temperatures across Kentucky at 3:25 AM Sunday: