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FXUS64 KMRX 040833 AFDMRX

Area Forecast Discussion National Weather Service Morristown TN 333 AM EST Mon Dec 4 2023

New SHORT TERM, LONG TERM

SHORT TERM
(Today and tonight)
Issued at 319 AM EST Mon Dec 4 2023

Key Messages:

1. A low pressure system will bring scattered light showers north of I-40 today, with gusty SW winds south of I-40.

A low pressure system is located over MO this morning, with a weak front extending E-SE across western KY into the I-40 corridor of Middle and East TN. The low will ride along this boundary today.
As seen by current radar over MO, most of the precip is on the eastern and northern sections of the low, and models show this continuing as it moves into our area by the afternoon. Moisture is shallow and forcing is weak, but there will be some steep midlevel lapse rates to generate scattered showers, mainly north of I-40 between 15-00Z. For areas south of I-40, most locations should remain rain-free with partly sunny skies, but the pressure gradient on the southern side of the low will induce gusty W-SW winds up to 25-30 mph. Gusts should subside with sunset with loss of boundary layer mixing and the movement of the low to the east of the mountains.

Some light precip may linger in the mountains with a W-NW upslope flow, but moisture appears too shallow for this to persist for more than a couple hours. A few light flurries or snow showers cannot be ruled out for the mountain peaks. Low clouds may linger in the Valley tonight as the NAM shows a layer of moisture below 850 mb that gets dammed by the mountains in the weak NW flow.

LONG TERM
(Tuesday through Sunday)
Issued at 319 AM EST Mon Dec 4 2023

Key Messages:

1. Shortwave trough brings colder air and a NW flow pattern, with accumulating snowfall expected in the higher elevations Tuesday night and Wednesday.

2. Higher pressure and ridging aloft to quickly warm area up Thursday and Friday.

2. Potential for a stronger system with significant rainfall and winds to affect the region Saturday into Sunday.

Discussion:

Little change since the earlier forecast for the long term period.
The next shortwave will be diving into the area late Tuesday and Tuesday night into Wednesday morning. Colder air will accompany this system as upper trough deepens over the eastern states. The system will move out of the upper midwest and western Great Lakes Tuesday and into the upper Ohio and eastern Tennessee Valley late Tuesday and Tuesday night. This almost due south plunge of cold air the shortwave is bringing with it and decent low level moisture and an upslope flow will combine together to produce some snowfall accumulations in the higher eastern Tennessee and southwest Virginia mountains. There will also be some light snowfall over the northern Cumberland Plateau and northeast Tennessee Valley as well as southwest Virginia valleys but amounts not that significant.
Accumulations will only be a dusting to a trace in the lower elevations. Lows Wednesday will only drop into the mid to upper 30s in the valley but upper 20s to lower 30s higher elevations. Advisory level amounts are expected above about 3 to 4 thousand feet in the Smoky Mountains and northeast Tennessee mountains. Most of the snow will fall late Tuesday night and Wednesday morning. Tuesday temperatures will be in the mid 40s to mid 50s during the day so the ground will still be warm making it harder for the snow to stick at night. Wednesday with the strong cold air advection and cloud cover highs will struggle to reach freezing in the higher elevations and only upper 30s to lower 40s northern Tennessee and southwest Virginia. Current forecast highs may still be a little warm in the northern areas due to the strong cold air advection.

The precipitation will end quickly Wednesday afternoon to around sunset and the cold upper trough will be exiting stage right. High pressure at the surface and aloft will slide back in for a quick warmup Thursday after a cold early morning in the 20s areawide.
Highs will rebound some 10 degrees above Wednesday, possibly more than that in the higher elevations but some snow cover could keep it cold. This fast warmup will continue Friday as surface high shifts east of the Appalchians and a southwest flow aloft returns.
Temperatures will be above normal and skies mostly sunny.

Ensembles then show a deepening trough moving into the central states and low pressure over the southern plains Friday night pushing a large area of moisture northeast. This low pressure and associated cold front will spread a warm airmass and showers eastward Saturday into the forecast area. The surface low looks to deepen as it moves northeast into the Ohio Valley. This could produce some locally heavy rainfall and possible thunderstorms ahead of it Saturday night into Sunday. Highs again Saturday in the 60s, the warmest day of the week but cooling into the 50s Sunday. Winds could become strong ahead of the front as well. Much cooler Sunday night with more winter precipitation possible behind this system.

AVIATION
(06Z TAFS)
Issued at 1218 AM EST Mon Dec 4 2023

Mid and high clouds will be over the area through the rest of the night and tomorrow morning. A low pressure system is expected to cross the area during the day, and it will likely bring some gusty winds to TYS and CHA in the afternoon as the associated cold front moves through. A few showers may accompany the front at TRI, but conditions should remain predominantly VFR.

PRELIMINARY POINT TEMPS/POPS
Chattanooga Airport, TN 60 38 56 39 / 0 0 0 10 Knoxville McGhee Tyson Airport, TN 58 39 52 38 / 10 0 10 70 Oak Ridge, TN 57 37 53 38 / 20 0 10 60 Tri Cities Airport, TN 52 36 48 35 / 30 10 20 80

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

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