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FXUS64 KMRX 080334 AFDMRX

Area Forecast Discussion National Weather Service Morristown TN 1034 PM EST Thu Dec 7 2023

New UPDATE

UPDATE
Issued at 1028 PM EST Thu Dec 7 2023

Bulk of the forecast is on track tonight, adjusted the temperature grids slightly for a handful of locations that were several degrees cooler than forecast. Patchy high clouds moving across the area will continue to do so overnight. Forecast is otherwise on track.

SHORT TERM
(This evening through Friday)
Issued at 244 PM EST Thu Dec 7 2023

Key Messages:

Mostly clear skies and a warming trend continues today and tomorrow.

Discussion:

Currently clear skies under high pressure near the surface and increasing ridging moving in from the west in the mid and upper levels of the atmosphere. Southwest winds are starting to see an uptick this afternoon, but will calm down once the sun begins to set. Quiet weather continues overnight tonight with passing high level clouds coming out of the southern plains towards the east coast expected to make a short appearance before we begin to clear out again tomorrow. Tomorrow will see temperatures around 5 degrees warmer today with the ridge strengthening over the region and southerly to southwesterly winds increasing again bringing in warmer

LONG TERM
(Friday night through next Thursday)
Issued at 244 PM EST Thu Dec 7 2023

Key Messages:

1. A strong system is expected Saturday through Sunday night.
Threats include: High winds and mountain waves, widespread rainfall with some rumbles of thunder, with likely minor accumulating snow in the high terrain areas. Light snow accumulations now possible for the Cumberland Plateau, northeast TN, and southwest VA.

2. Dry conditions expected Monday through Thursday.

Discussion:

See key message 1 for weekend overview.

Rain:

Precip chances begin to increase Friday night ahead of our incoming long wave trough and cold front. Light and scattered showers are expected with QPF amounts less than one tenth of an inch. Light and scattered showers continue on Saturday with increasing POPs through the day with QPF generally less than one tenth of an inch. There is still some slight model disagreement on when the heaviest rain arrives, whether it's midnight Saturday or holds off until Sunday morning. It really depends on the progression and speed of the cold front. Nonetheless, as the moderate rain moves through the area, storm total QPF will range from 1.5 to 2.5 inches for most places.
The heaviest precip exits late Sunday afteroon with a few light lingering showers through Sunday evening. WPC has our area under a marginal risk of excessive rainfall for when the heaviest precip moves through. Also, a few rumbles of thunder can't be ruled out due to minor elevated instability Saturday night into Sunday morning.

Wind:

Southwest flow ramps up from Friday night through Saturday. 850mb winds will generally range from 30 to 40 knots through the day on Saturday. Winds will breezy across the higher elevations of the east TN mountains with gusts from 25 to 35 mph. The 850mb winds further increase Saturday night through Sunday morning just ahead of the cold front with speeds from 40 to 50 knots. During this time mountain waves are likely due to favorable wind/slope alignment.
Wings gusts from 40 to 50 mph appear likely with our highest peaks, such as Cove Mountain TN, gusting to 60 mph. Other locations such as the Cumberland Plateau, and the mountains of southwest VA and NC, will see gusts from 30 to 40 mph. A Wind Advisory will likely be needed within the next day or two. Winds lessen in intensity behind the cold front but remain breezy with 20 to 30 knots of 850mb flow out of the northwest.

Snow:

Now that some of the higher res guidance is starting to come in, mainly the NAM. It appears increasingly likely that the higher elevations of the east TN and southwest VA will see at least some minor accumulating snowfall with this system. Soundings show a rapid changeover of rain to snow Sunday afternoon as cold air plunges into the area. There will be a narrow window of time where snowfall rates will be moderate before the moisture dries up Sunday evening. The current forecast calls for up to 2 inches above 4000 feet and 0.5 to 1 inch above 3000 feet across the east TN and southwest VA mountains. Trace amounts up to a few tenths of an inch are possible across the northern Cumberland Plateau, northeast TN, southwest VA and southwest NC. The rest of the east TN Valley will likely see a few flakes flying around as well but no accumulation expected. The rain/snow transition won't occur in valley locations until Sunday evening, as the bulk of the moisture has already exited.

Below normal temperatures expected Monday behind the cold front with temps slowly moderating thorugh the rest of the extended along with dry conditions.

AVIATION
(00Z TAFS)
Issued at 634 PM EST Thu Dec 7 2023

VFR and dry conditions through TAF period. A band of high clouds will traverse through overnight. Light winds will flow up the Tennessee valley tomorrow.

PRELIMINARY POINT TEMPS/POPS
Chattanooga Airport, TN 37 61 50 64 / 0 0 40 70 Knoxville McGhee Tyson Airport, TN 36 60 46 67 / 0 0 30 50 Oak Ridge, TN 36 59 46 64 / 0 0 30 50 Tri Cities Airport, TN 32 57 37 65 / 0 0 10 20

MRX WATCHES/WARNINGS/ADVISORIES
NC...NONE.
TN...NONE.
VA...NONE.

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