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FXUS64 KMRX 061720 AFDMRX

Area Forecast Discussion National Weather Service Morristown TN 1220 PM EST Wed Dec 6 2023

New AVIATION

UPDATE
Issued at 940 AM EST Wed Dec 6 2023

Morning update to make only some minor tweaks to PoPs over the next several hours as a few light bands of precipitation continue to move in from Kentucky. Based on Dual Pol data the melting layer is somewhere between 2,800 - 3,100 feet above sea level. So locations above this could still see some light flurries with precipitation bands, while rain is expected below 2,500 feet.
Light precipitation could continue into the early afternoon along the mountains as the LLJ begins to increase and could squeeze out any lingering low level moisture. For most of the valley locations the forecast remains unchanged.

SHORT TERM
(Today and tonight)
Issued at 309 AM EST Wed Dec 6 2023

Key Messages:

1. Rain and snow showers will be tapering off later this morning.
Additional light accumulations are possible in the higher elevations after sunrise. The Winter Weather Advisory continues.

2. Colder temperatures today with highs in the 40s and lows tonight in the 20s.

Discussion:

We are likely at the peak of precipitation with the passage of a mid/upper level trough axis. Current surface obs in the lower elevations show precip is all rain, but obs sites in the mountains above ~2500 ft are showing temperatures in the upper 20s to lower 30s. The Newfound Gap sensor is reporting 27 degree and snow accumulation of 1.75 inches as of 3 AM, with rates of 0.5-1 inch per hour. Radar trends suggest this will continue for a few more hours. Snow is also falling at Beech Mountain, NC, so locations near the TN border such as Roan Mountain are likely seeing snow as well. KLNP has just started reporting snow. Forecast soundings suggest that lapse rates will continue to steepen over the next few hours. Based on this information, the current Advisory and forecast snow amounts appear to be in good shape, so little change is needed. Still expecting around 1 inch for elevations above 2500 ft, with around 3-5 inches above 4000 ft.

Lapse rates, moisture depth, and NW 850 mb winds decrease this afternoon as the trough continues to exit to the east. Measurable precip should end in most spots by 18Z, although some flurries/sprinkles may linger in SW VA past that time. Although there will be partial clearing of clouds, especially in the lee of the Plateau, cold advection will hold high temps in the 40s in most locations. High pressure builds over the area tonight, and with calm winds and clearing skies, lows will drop into the 20s.

LONG TERM
(Thursday through Tuesday)
Issued at 309 AM EST Wed Dec 6 2023

Key Messages:

1. Dry weather is expected Thursday and Friday.

2. A strong system is expected Saturday night through Sunday night.
Could bring mountain wave winds, widespread rainfall, some rumbles of thunder and even some snow in the higher terrain Sunday night.

Discussion:

Thursday through Saturday morning will be dry with a ridge and high pressure over the Southeast. Temps will be seasonable with highs in the 50s.

A deep trough will move into the Mississippi Valley on Saturday.
Model guidance is in better agreement now on the position of the trough and surface low. GFS and ECMWF are in much better agreement on timing. Both have the system moving slowly through the region.
QPF has gone up considerably for this reason. Storm total QPF is now 1 to 2 inches areawide. The best chance for rain will be Saturday evening through Sunday. A few rumbles of thunder will be possible but overall instability will be low with dew points in the 50s.
Winds will increase ahead of this system by Saturday afternoon or evening. Mountain wave winds will be possible with guidance currently suggesting 850mb winds in the 40 to 50 knot range from the south or southwest Saturday night. The Plateau could also see gusty winds with 850mb winds 40 to 50 knots from Saturday afternoon through Saturday night. So far NBM winds for that timeframe do not look that impressive with gusts around 30mph to 35mph Saturday night for the Plateau and mountain wave prone areas of the East TN mountains.

A changeover to rain/snow mix will be possible Sunday evening into Sunday night for the higher elevations including the Plateau and SW Virginia. Model guidance suggests a broad trough behind this system with flow that is more westerly or zonal. Without good forcing, little to no accumulation is expected.

Monday and Tuesday looks to be dry with seasonable temperatures with high pressure and slight troughing or nearly zonal flow in place.

AVIATION
(18Z TAFS)
Issued at 1216 PM EST Wed Dec 6 2023

Ceilings are slowly lifting as the drier air from the northwest makes its way into the region. Expect mid level ceilings to stick in for a while, before burning off. Fog will be possible overnight, but will wait to see how much clearing occurs before confidence increases on where fog is most likely.

PRELIMINARY POINT TEMPS/POPS
Chattanooga Airport, TN 31 57 37 61 / 0 0 0 0 Knoxville McGhee Tyson Airport, TN 29 54 36 60 / 0 0 0 0 Oak Ridge, TN 27 54 36 58 / 0 0 0 0 Tri Cities Airport, TN 26 51 33 57 / 0 0 0 0

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

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