textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Precip chances have increased slightly tonight thru Sunday morning, but still only minimal snow accumulations expected.

Otherwise, no changes since Saturday afternoon.

KEY MESSAGES

1. Light snow possible across the mountains tonight, with a mix of light rain and snow across most of the Piedmont tonight through Sunday morning. Some minor snow accumulations possible, but with little to no impact to area roads expected. 2. Another cold air mass spreads over the region by the middle of next week. A Cold Weather Advisory may be needed for a portion of the mountains Monday night into Tuesday. 3. A weak cold front crosses the area Thursday with a small precip chance. Another frontal system may affect the area Saturday but this is highly uncertain.

DISCUSSION

Key message 1: Light snow possible across the mountains tonight, with a mix of light rain and snow across most of the Piedmont tonight through Sunday morning. Some minor snow accumulations possible, but with little to no impact to area roads expected.

A strong 500 mb vort lobe will rotate and sharpen a deep longwave trough axis over the Lower MS Valley tonight, then track thru the Southeast Sunday. This feature will provide strong mid and upper-level forcing and help produce a band of low-to-mid-level frontogenesis along a stalled cold front along the Appalachians to the central Gulf Coast. SW flow along the front will tap into enough moisture to bring some precip chances into the forecast area tonight. The 12z guidance has come into pretty good agreement on this setup and produces a band of light precip from the FL Panhandle north into the Mid-Atlantic tonight. This is a westward jog from previous model runs, so PoPs have trended up. However, with the front set up over the mountains, the air across the Piedmont has trended warmer as the precip develops overnight. So, snow chances remain only in the chc range for most of the region. Precip will likely start out as mostly rain (except perhaps all snow in the highest elevations), then start mixing with snow and even changing over to all snow in the areas of highest precip rates and at the tail end of the precip shield as it pivots east early Sunday morning. Given temps in the lower 40s to mid 30s thru most of the precip event, even once snow falls, it should mostly stick to elevated and grassy surfaces. But localized areas of around half an inch, which may stick to some bridges/overpasses and secondary roads, cannot be ruled out. Confidence on where that may occur in our CWFA is too low to predict. So for now, have a broad area of mainly 0.1-0.2" of snow accums by 8 am Sunday across most of the Piedmont. Whatever does fall should melt fairly quickly, the front shifts east and temps warm into the upper 30s to lower 40s and the clouds start to clear out from west to east. Will continue to mention in the HWO, and an SPS may be needed if confidence increases, but a Winter Weather Advisory does not appear to be warranted.

Key message 2: Another cold air mass spreads over the region by the middle of next week. A Cold Weather Advisory may be needed for a portion of the mountains Monday night into Tuesday.

A strong area of surface high pressure and a cold air mass will move into the area behind a dry cold front on Monday. The guidance has trended warmer with this system; however, lows Monday night look to be 10 to 15 degrees below normal. Still, with the breezy conditions Monday night into Tuesday morning, wind chill values look to fall below zero for the higher elevations. A Cold Weather Advisory may be needed, especially for the higher elevations. Tuesday night will be nearly as cold but lighter winds keep wind chills above critical values. Tuesday will be the coldest day with highs 10 to 15 degrees below normal.

Key message 3: A weak cold front crosses the area Thursday with a small precip chance. Another frontal system may affect the area Saturday but this is highly uncertain.

A short wave rotates through the deep upper trof over the eastern CONUS Thursday taking the trof axis with it with zonal flow developing Friday and Saturday. The guidance is coming in better agreement on a weak cold front associated with the short wave crossing the area Thursday. Forcing is weak over our area and moisture will be limited. This results in only a slight chance of a wintry mix for the NC mountains Wed nite and Thu morning. There is still some uncertainty but the chance of any impacts looks very low at this time. Another frontal system may affect the area on Saturday; however, there is little model to model or run to run consistency. Therefore, confidence is very low for this part of the forecast. Have followed the model blend which does bring a chance of rain in on Saturday with temps a little above normal.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: Moisture and lift associated with an area of low pressure developing off the Carolina Coast will result in lowering cigs and increasing precip potential across the Terminal Forecast Area tonight. The highest probability for precip and restrictions will be at KCLT, KGSP, and KGMU, where at least tempo MVFR cig and visby conditions and -RA are forecast between 06Z and 12Z. Probabilities are lower at the other sites, but at least Prob30 MVFR conditions are advertised there. This includes a Prob30 for -SNRA at KAVL from 04-08Z.

As colder air spills into the lower elevations between 09-12Z, the potential for -SN will also develop at most other TAF sites, with Prob30s for at least a -SN/RA mix included in the forecast. Also can't rule out a period of IFR conditions circa 12Z Sunday, but confidence is low at this time. Precip potential will diminish and cigs steadily improve through the morning (except perhaps at KCLT), with VFR conditions expected at most sites by mid-afternoon. Light SW winds this evening are expected to become WNW at 5-10 kts throughout the morning.

Outlook: Dry high pressure builds in Sunday night thru midweek, keeping VFR conditions across the region.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...None. SC...None.