textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Aviation discussion updated for the 00Z TAFs.

KEY MESSAGES

1. Frosty temperatures are likely again tonight and on Monday night, even as high temperatures warm above normal. 2. A strong frontal system increases precipitation chances late in the week, including the potential for mountain snow as much colder air overtakes the region.

DISCUSSION

Key message 1: Frosty temperatures are likely again tonight and on Monday night, even as high temperatures warm above normal.

Heights will steadily rise, while a ridge of dry high pressure will remain over the Southeast through mid-week. The result will be warm/above-normal (by around 5 degrees) high temps Mon through Wed. The dry air mass will support large diurnal temperature ranges, with near-to-below normal lows forecast. Good radiational cooling conditions will support temperatures cool enough for frost formation across the NC foothills and northwest Piedmont tonight, and a Frost Advisory has been issued for these areas. Another round of frost is possible across these same areas Mon night...which incidentally will be the last night that Frost/Freeze products will be issued for any part of our area until the spring growing season begins.

Key message 2: A strong frontal system increases precipitation chances late in the week, including the potential for mountain snow as much colder air overtakes the region.

Global models remain in agreement in strongly amplifying the upper air pattern by mid-week, with a massive ridge building across the West. Multiple short wave troughs originating from increasingly higher latitudes will dive down the central-to-east part of the Conus during the latter half of the week, carving out of an anomalous long wave trough/upper low over the East by Friday. Associated arctic frontal zone is forecast to cross our area in the late Thursday/Thu night time frame. Surface low is likely to cross the central Appalachians/Mid-Atlantic before intensifying as it moves off the Mid-Atlantic coast late Friday. The emerging guidance consensus is that moisture interaction with the frontal system will be such that the chances for organized warm sector precip will be low, and PoPs are generally limited to 20-30% ahead of the front. However, as the surface low intensifies Friday into Fri night, so will northwest/cold advection flow across the southern Appalachians and vicinity. This will interact with post-frontal moisture to result in upslope/wrap-around showers. With snow-levels falling quickly during this time frame, mountain snow showers are likely for at least the high elevations, and confidence is increasing that accumulating snow will occur. While confidence is highest that snow will accumulate above 3500 feet along the TN/NC border, accums are possible in favored valley locations of the TN border counties as well. Otherwise, temps will decrease from around normal on Thursday/Thu night, to a solid 10+ degrees below climo Friday through at least Sat night. Much of the area outside the mountains is likely to finally experience the first freezing temps of the season next weekend.

AVIATION /00Z MONDAY THROUGH FRIDAY/

At KCLT and elsewhere: Dry and VFR through the 00Z TAF period. If patchy mountain valley fog/low stratus develops, it should not reach KAVL. Winds will remain WNW/NW at KAVL through the period, with low- end gusts developing by Monday afternoon. Lighter wind speeds are expected east of the mountains through the period, starting out SW this evening before gradually turning more WNW/NW overnight. Mostly SKC but a few cirrus may track overhead briefly Monday morning.

Outlook: Dry and largely VFR through Wednesday, outside of some patchy mountain valley fog/low stratus each morning. A cold front may bring precipitation and associated restrictions Thursday into Friday but confidence is low at this time.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...Frost Advisory from midnight tonight to 9 AM EST Monday for NCZ035>037-056-057-068-069-502-504-506-508. SC...None.