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FXUS61 KRNK 100101 AFDRNK

Area Forecast Discussion National Weather Service Blacksburg VA 801 PM EST Sat Dec 9 2023

SYNOPSIS
A strong cold front brings a soaking rain late tonight into Sunday. Rain changes to snow behind the front Sunday night before ending east of the mountains, with snow showers likely into Monday across the mountains. High pressure builds in Monday night through midweek.

NEAR TERM /THROUGH SUNDAY/
As of 800 PM EST Saturday...

Forecast remains on track. For the evening update, the only thing additional was to add fog along southern Blue Ridge for the overnight. Remainder of the forecast is unchanged.

Key Messages:

1) Soaking rains late tonight into Sunday. Localized flooding issues possible.

2) Cannot rule out a thunderstorm, with locally damaging wind gust not out of the question east of Danville/Reidsville.

Rain will develop overnight and continue through the day Sunday as cold front along with several low pressure waves arrive in the mountains with powerful 130-150kt jet moves from the TN Valley into New York with the RRQ arriving around 12z. As the 5h trough deepens across the MS Valley, the front starts to get closer to parallel with the upper flow, hence slowing it down. This will allow for areas to receive 1+ inches of rain.
Latest trends favor along/east of the Blue Ridge getting more rain than the mountains.

We have been dry, so antecedent conditions aren't too much of a concern in terms of flash flooding or river flooding. However, given the drier ground, runoff from heavier downpours could result in urban/street flooding and the typical ponding of water on roads, and some narrow culverts overflowing. So not seeing any need for any headlines, as the entire forecast area is in a marginal risk of excessive rainfall.

There is also a chance for stronger storms in the piedmont. Early in the day, models show elevated instability moving from WV to the piedmonts of VA/NC through the day Sunday. Have allowed for just a slight chance of thunderstorms given the strong system dynamics, but no thermodynamics to speak of as we stay cloudy for much of the period overnight-Sunday.

The main concern is the strong shear which could sample the higher winds with showers to bring isolated damaging wind gusts to the piedmont. Confidence is low on severe potential at this time though given cloud cover in place which usually limits winds mixing to the surface.

The front should be across the piedmont by dusk, with colder air lagging about 1-3 hrs behind the front. At this time any snow looks to hold off til dusk or thereafter in the mountains, so limited accumulation for Sunday if any. More about the snow and winds in the Short Term discussion.

Temperatures overnight are expected to remain relatively mild with readings steady or rising ahead of the front...lows in the upper 40s to mid 50s.

Sunday will see temperatures warm early to midday in the lower to mid 60s east, with 50s west, with temperatures falling into 30s and 40s around dusk in the mountains.

Forecast confidence is highest on the entire forecast area getting much needed rainfall late tonight-Sunday. Moderate confidence on temperatures/winds and sky cover, low on severe and flooding threat.

SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/
As of 1220 PM EST Saturday...

Confidence is high for gusty winds and mountain snow showers during Sunday night into Monday, then dry weather returns afterward.

As a cold front moves east of the Mid Atlantic on Sunday night, the wind should shift from the southwest to the northwest. Rain should eventually diminish across the Piedmont due to the increasing downslope flow, but upslope flow will allow the moisture to continue west of the Blue Ridge. With temperatures falling below freezing in the mountains, any rain will transition to snow showers. The highest snowfall accumulations during Sunday night and Monday will be found in western Greenbrier County where one to three inches are possible.

The wind should become gusty by early Monday morning with gusts possibly reaching up to 50 mph, or near wind advisory criteria. The most favorable areas for the strongest wind gusts will be along the southern Blue Ridge from Watauga County to Grayson County. It will take until Monday evening for the gusty northwest wind and the mountain snow showers to gradually fade. High pressure should build across the Appalachian Mountains by Monday night, which will set up more favorable radiational cooling to allow temperatures to plunge into the teens and 20s. Dry weather will persist through Tuesday and Tuesday night as temperatures slowly moderate.

LONG TERM /WEDNESDAY THROUGH SATURDAY/
As of 1220 PM EST Saturday...

Confidence is high for dry weather through the remainder of the week with high pressure in control.

High pressure will remain in firm control across the Mid Atlantic for the remainder of the week. Even though an upper level trough will pass to the north on Wednesday, dry weather should persist throughout this time period. Temperatures should trend roughly close to normal values for this time of year. Model agreement does start to break down a little by Saturday due to discrepancies with an area of low pressure forming somewhere along the Gulf Coast. However, it is way too early to introduce any rainfall chances as the vast majority of the models keep it dry through Saturday.

AVIATION /01Z SUNDAY THROUGH THURSDAY/
As of 800 PM EST Saturday...

Clouds and precip will increase in coverage for the overnight as a strong cold front approaches from the west. Included wind shear for all terminals per strong low level jet ahead of the front.

Ceilings/vsbys are expected to trend lower overnight with potential for IFR/LIFR late tonight and early Sunday.
Expecting mainly light rain or drizzle prior 12z, then moderate to heavier showers are likely in the 12-18z time frame with ceilings/vsbys in the IFR or lower category.

Surface winds will mainly be out of the south at 5-10kts overnight, then some gusty winds ahead of the front to 18-30kts possible Sunday morning btwn 12-18z, becoming southwest to west at BLF/LWB and BCB by 18z, and westerly across the remaining terminals after 18Z.

Some models show elevated instability so cannot rule out a thunderstorm in the 12-18z time frame, but too isolated for tafs.

Forecast confidence is average on the early showers and chance of VFR, and above average on sub-VFR after 04z tonight, and especially around/after 12z Sunday.

Extended Aviation Discussion...

Cold front will cross the area on Sunday afternoon, bringing widespread rain and MVFR to LIFR ceilings through Monday morning. Rain changes to snow Sunday evening in the mountains with snow shower/flurries possible as far east as LYH/DAN by 12z Monday, so not seeing much improvement in aviation conditions until during the day Monday with northwest flow and high pressure clears things out/lifts to VFR east of the Blue Ridge, while the WV mountains linger in sub-VFR and snow showers/flurries for most of Monday with conditions improving Monday night. West to NW winds develop behind the frontal passage Sunday evening into Monday, with winds gusting to 25-30 kts at TAF sites, and stronger winds aloft.

Tue-Thu look dry with VFR.

RNK WATCHES/WARNINGS/ADVISORIES
VA...None.
NC...None.
WV...None.

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Falling Creek entrance
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