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FXUS64 KMRX 090737 AFDMRX

Area Forecast Discussion National Weather Service Morristown TN 237 AM EST Sat Dec 9 2023

New SHORT TERM, LONG TERM

SHORT TERM
(Today and tonight)
Issued at 132 AM EST Sat Dec 9 2023

Key Messages:

1. Light and scattered rain showers today ahead of an approaching cold front.

2. Heavier showers and some storms tonight as a cold front moves through. A few storms may be strong to severe overnight.

2. Winds become strong and gusty across the east TN mountains, especially tonight.

Discussion:

Scattered showers will continue to develop and move through the region this morning as a strong system approaches from the west.
Guidance is in agreement that showers will become more spotty by this afternoon with the main round of showers and storms expected this evening and overnight. Southerly winds will increase today with a strong 850mb jet just to the west. The strongest winds will be in the Plateau counties of Morgan, Scott and Campbell and in the East TN mountains and foothills. Gusts around 30 mph are expected at those locations through this afternoon. After sunset, conditions will become more favorable for downslope wind enhancement in the East TN mountains and foothills as the 850mb jet moves east into the region. The 850mb jet will likely peak around 35 to 40 kt in the mountains overnight. Advisory level winds can be expected in the east TN mountains and foothills starting this evening with gusts up to 50 mph possible in mountain wave prone areas. Winds will be lighter in the Tennessee Valley but gusts up to 25 mph will be possible mainly this afternoon and evening mainly in the Southern and Central Valley.

HRRR guidance looks more favorable for thunderstorms tonight with a line moving through late this evening into the overnight hours.
A few storms may be strong to severe. SPC has most of the region outlooked in marginal risk with a slight risk in our westernmost counties. Low instability will be a limiting factor for storm organization with dew points struggling to reach 60 and very low CAPE expected. However, shear is favorable. The main threat will be damaging winds but a brief, weak tornado spinup or two cannot be ruled out with 0-1 km shear very favorable around 30 knots as the front approaches. Again, low instability will be a limiting factor.

Rain totals through the weekend haven't changed much. Still expecting 1 to 2 inches of widespread rain throughout the whole weekend. Some spots may even see some minor flooding issues as the main line moves through. A lot of the guidance has the line moving through slowly.

LONG TERM
(Sunday through Friday)
Issued at 132 AM EST Sat Dec 9 2023

Key Messages:

1. A strong cold front will move across the area on Sunday with heavy rain at times and gusty winds. Temperatures drop with rain changing to snow across the higher elevations.

2. Dry conditions expected Monday through Friday with high pressure and initially cold temperatures Monday warming through the week.

3. Another system may bring precipitation to the region Friday night into Saturday next weekend.

Discussion:

A cold front will be moving west to east across the forecast area on Sunday with an amplifying longwave trough and cold air advection across the region. With ample moisture, total rainfall of 1 to 3 inches is expected across the region with this system. In the wake of the cold front, boundary layer winds shift to the northwest with 850mb flow of around 20 kt. This will provide ample support for orographically enhanced lift across the higher elevations.

RAP forecast soundings show saturation up to about the -10C level.
While not saturated through a large portion of the DGZ, this will be sufficient for northwest flow snowfall and rime ice across the higher terrain. Most model guidance is favoring 1 to 3 inches of snow across the higher elevations of the mountains with locally higher amounts possible across the highest peaks. Most snowfall will be limited to areas around 2500 feet elevation and above across the East Tennessee and southwest Virginia mountains. No measurable accumulation is expected across the valley with perhaps a light coating for portions of the plateau.

Snow begins to taper off to flurries on Monday morning across the mountains with dry air moving into the region. With longwave troughing and a cold surface airmass, temperatures will be close to 10 degrees below normal on Monday.

As the longwave trough begins to lift with ridging building in late week, temperatures begin to warm with a moderating surface airmass.
With high pressure in control, we remain dry through the end of the week.

As we approach next weekend, a strong shortwave is expected to move across the Lower Mississippi Valley with cyclogenesis across the Southeast CONUS. This may bring precipitation to our area on Friday night into Saturday, but uncertainty with the exact track and location of this system is still high.

AVIATION
(06Z TAFS)
Issued at 1211 AM EST Sat Dec 9 2023

Showers will develop and move through the region overnight and this morning ahead of an approaching frontal system. MVFR CIGs have already moved in to the Southern TN Valley. MVFR CIGs are expected through this TAF cycle at CHA with IFR possible this morning and after sunset tonight. TYS will likely see MVFR CIGs this morning with showers but improving to VFR this afternoon with showers becoming more spotty. TRI will see the least impact weather with VFR conditions and spotty showers. After sunset tonight rain chances increase significantly as a cold front approaches. Some thunder will be possible tonight and TSRA will likely be in the next TAF package.

PRELIMINARY POINT TEMPS/POPS
Chattanooga Airport, TN 64 48 59 31 / 60 100 80 10 Knoxville McGhee Tyson Airport, TN 66 49 59 31 / 40 100 90 30 Oak Ridge, TN 64 47 58 30 / 40 100 90 20 Tri Cities Airport, TN 66 51 60 30 / 30 90 100 70

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

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