textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated for new Aviation discussion. Minor tweaks to precip chances through Thursday morning.

KEY MESSAGES

1. A strong cold front arrives tonight into Thursday morning bringing widespread showers and thunderstorms, with a very low-end severe weather threat. A brief transition to a wintry mix is expected across the mountains Thursday morning, with light accumulations possible across the higher elevations. 2. Cooler and drier conditions will spread over the region late Thursday and linger thru Saturday. Rain chances return Sunday into Monday, with some snow showers possible near the TN border Monday. 3. Much colder air returns behind a strong cold front Monday night through at least Wednesday. Most areas will likely see freezing low temperatures both Tuesday morning and Wednesday morning.

DISCUSSION

Key message 1: A strong cold front arrives tonight into Thursday morning bringing widespread showers and thunderstorms, with a very low-end severe weather threat. A brief transition to a wintry mix is expected across the mountains Thursday morning, with light accumulations possible across the higher elevations.

A southern stream trough over the Southern Plains will phase with a northern stream trough over the Central Plains today into tonight. This mean trough will swing across the Appalachians tonight into tomorrow morning with height falls overspreading the region. An accompanying surface cold front will crash across the mountains and across the area with an associated band of showers and thunderstorms. Robust wind fields translating across the Carolinas will foster 50-60kts of deep-layer vertical wind shear with 30-35kts of 0-1km shear. In addition, moisture pooling ahead of the boundary will promote a narrow warm sector characteristic of 150-250 J/kg of surface-based CAPE. While not impressively buoyant, strong forcing will help to maintain a convective line into the area overnight into early Thursday morning. A lead portion of the line will push into the mountains late this evening out of east Tennessee, but likely won't make it much farther east. A second line is forecast to develop over Georgia overnight and lift into the Upstate with the potential for an isolated severe weather threat along and south of I- 85. Deep-layer shear is largely parallel to the line, but if any linear segments can surge to the northeast an isolated severe weather threat cannot be discounted. This would be in the from of locally damaging winds and perhaps an isolated tornado. Showers and areas of moderate rain linger behind the line through the morning before clearing out by late morning to early afternoon. Winds will remain gusty overnight and then again behind the front tomorrow. Temperatures will fall behind the front and struggle to warm into the low 50s tomorrow afternoon.

Key message 2: Cooler and drier conditions will spread over the region late Thursday and linger thru Saturday. Rain chances return Sunday into Monday, with some snow showers possible near the TN border Monday.

Cool and dry high pressure briefly settles over the area Thursday night into Friday, bringing back down to a few deg below normal for the first time in a couple weeks. Temps generally 20 deg cooler than the last couple days will be a sharp contrast. Temps rebound somewhat Friday, with highs near normal, then warm to about 5-10 deg above normal for Saturday, as high pressure slides east and brings a return-flow regime.

The next storm system will organize over the Plains Saturday into Sunday, bringing a warm front thru the area. This front may produce isolated to scattered showers, as some sbCAPE works into the area from the SW. Then a cold front will push into the area Sunday night and exit to the east late Monday. Some instability and shear may support a non-zero severe tstm threat. QPF does not look to be that heavy. Models are mixed on how much moisture will linger in NWLY flow behind the front, but an inch or two is possible above 3500 ft along the TN border, before the precip tapers off Monday evening. Monday will be transition day with respect to temps, with lows starting out well-above-normal, then highs near normal and generally falling temps thru the day.

Key message 3: Much colder air returns behind a strong cold front Monday night through at least Wednesday. Most areas will likely see freezing low temperatures both Tuesday morning and Wednesday morning.

A deep upper trough will dig across the middle of the country Monday and set up across the eastern CONUS Tuesday thru at least Wednesday. This will allow a Canadian high pressure system to settle into the region behind a strong cold front. Temps will fall to 5 to 10 deg below normal Monday night, with highs 15 to 20 deg below normal Tuesday. Lows will likely range from the teens to mid 20s in the mountains, and upper 20s to lower 30s across the Piedmont, both Monday night and Tuesday night. While the growing season usually doesn't start this early, the recent very warm weather may be resulting in some tender vegetation blooming, which may be vulnerable to this cold snap. Otherwise, dry conditions expected.

AVIATION /00Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: VFR conditions thru the evening hours with gusty SW wind continuing, then restrictions start moving in from the west in the pre-dawn hours. Convective line on radar over east TN at issuance time is expected to continue weakening and slowing down as it reaches the mtns during the mid-evening, thus the PROB30 at KAVL. It should take until after 07Z and thru 11Z for the leading edge of the precip and restrictions to move in west to east as the better forcing with the cold front finally moves in. Most of the guidance supports keeping the flight category mainly at MVFR for low ceiling. After about two hours, the front will move thru with an abrupt wind shift to NW or N, followed by an extended period of rain for the better part of the rest of the morning. Mainly MVFR is expected, but there could be occasional IFR vis in heavier rain. Cold air behind the front may change the precip over to snow along the TN border, but this is not expected to reach KAVL. Once the precip moves off to the east on Thursday, expect rapid clearing. Deep mixing will bring down frequent strong wind gusts from the NW and N thru the rest of the daylight hours. The wind finally weakens at KCLT after sunset as the boundary layer decouples.

Outlook: VFR from Thursday evening onward. Another cold front may bring showers and associated restrictions Sunday.

CLIMATE

RECORDS FOR 03-11

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 79 1967 29 1924 55 2016 14 1934 1925 KCLT 83 2015 37 1960 60 1986 22 1969 2009 1934 1990 KGSP 84 2009 34 1960 60 1986 17 1969

GSP WATCHES/WARNINGS/ADVISORIES

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