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FXUS64 KMRX 102359 AFDMRX

Area Forecast Discussion National Weather Service Morristown TN 659 PM EST Sun Dec 10 2023

New AVIATION

SHORT TERM
(This evening through Monday)
Issued at 249 PM EST Sun Dec 10 2023

Key Messages:

1. Light accumulating snowfall expected across the higher elevations of the east TN and VA mountains. Winter Weather Advisory remains in effect for the east TN mountain zones.

2. A Special Weather Statement has been issued for Wise, Russell, and Washington VA for sub-advisory snowfall amounts.

3. Much colder tomorrow with highs 5 to 10 degrees below normal.
Wind Chills will be in the 30s for most areas through the day and down into the teens in the mountains.

Discussion:

Not much change from the previous forecast in regards to snowfall amounts or timing for this evening through tomorrow morning. At the current hour, rain showers have mostly moved east of I-75. NAM soundings show rain showers will transition to snow between 18 and 20Z for areas above 5000 feet in elevation. This matches up well with what current MRX Dual Pol CC values show, paired with a few of our higher elevation observations. Dual Pol CC shows mixed precip is likely occurring somewhere between 5000 and 6000 feet MSL, with snow likely above 6000 feet. The temp at Newfound Gap as of 2 PM EST is 38 degrees and falling. The rain/snow line will quickly lower in elevation through this evening as cold air rushes in behind the cold front.

There is still a good fetch of moisture moving up across the Appalachians at the current hour. However, the bulk of the moisture moves east of our area between 00Z and 03Z as the trough axis slides east into NC. Prior to the deeper moisture exiting, expect moderate snowfall rates with wet snow. After 03Z, northwest flow snow begins to kick in across the favored upslope areas of the east TN and VA mountains. This will last through the night and gradually end tomorrow morning. Storm total snow, from this evening through tomorrow morning, will still range from 1 to 3 inches above 3500 feet. Locally higher amounts up to 4 inches are possible across the highest mountain peaks in TN. Due to trapped low level moisture, the lower elevations of northeast TN and southwest VA will likely see some light and scattered snow showers overnight but little to no accumulation expected. Special Weather Statement issued for Wise, Russell, and Washington VA for 1 to 2 inches of snowfall across the higher elevations.

Clouds will be slow to clear tomorrow as low level moisture remains trapped. Highs will be 5 to 10 degrees below normal with Wind Chill values in the 30s for most places and down into the teens across the mountains as northwest winds remain breezy.

LONG TERM
(Monday night through next Sunday)
Issued at 249 PM EST Sun Dec 10 2023

Key Messages:

1. Cold and dry Monday night with upper trough overhead and surface high pressure building in.

2. Warming temperatures middle to late week with a zonal flow aloft.

3. Another system to bring precipitation to the region on the weekend but timing uncertainty is still high.

Discussion:

The upper trough that brought the showers and storms overnight will have shifted to the northeastern states and a surface high pressure area will be replacing it with clear skies and cold temperatures overnight Monday night. Lows will be the coldest of the week early Tuesday in the 20s. Starting Tuesday temperatures warm to near and then above normal as surface high pressure settles in and then ridging aloft has temperatures above normal for the last 2 days of the week and continue this weekend. A southwesterly low-level flow returns to the region at the end of the week. This will help increase moisture in the lowest levels Friday night and Saturday.

The next part of the forecast this upcoming weekend is still not too clear. Models are continuing to vary and mostly keeping activity to the south across the southern states. On Saturday a northern shortwave digs southeast across the Great Lakes and a southern stream system developing near the Gulf Coast moves east across the southeast through Sunday. The GFS does bring moisture north into the southeastern Tennessee Valley and southern Appalachians Saturday night into Sunday. However, the forecast area may be caught in the middle and stay mostly dry with not much impact. With the bigger system to the south crossing part of the area Saturday night and Sunday will continue to have a chance of showers in for Sunday.

AVIATION
(00Z TAFS)
Issued at 606 PM EST Sun Dec 10 2023

Rain continues to move east this evening with some SHRA expected at TRI over the next few hours. Post frontal winds will continue from the north/northwest. Some slight amplification of the surface low to the east will result in a tightening of the pressure gradient and subsequent increase in northerly flow. This set of TAFs will feature sustained winds around 10 knots for much of the night eventually relaxing toward Monday afternoon. Low level cloud cover will continue for much of the area, especially TYS and TRI overnight and into Monday with MVFR forecast. Clouds will eventually move out by 18Z Monday. CHA should stay VFR overnight and on Monday.

PRELIMINARY POINT TEMPS/POPS
Chattanooga Airport, TN 31 49 30 53 / 0 0 0 0 Knoxville McGhee Tyson Airport, TN 31 44 27 51 / 10 0 0 0 Oak Ridge, TN 29 45 26 51 / 10 0 0 0 Tri Cities Airport, TN 30 40 24 49 / 70 0 0 0

MRX WATCHES/WARNINGS/ADVISORIES
NC...NONE.
TN...Winter Weather Advisory until noon EST Monday for Blount Smoky Mountains-Cocke Smoky Mountains-Johnson-Sevier Smoky Mountains-Southeast Carter-Southeast Greene-Unicoi.

VA...NONE.

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