textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated aviation discussion for the 12Z TAFs.

KEY MESSAGES

1. Scattered showers and isolated thunderstorms possible through the day. Near-record warmth returns today and continues through Wed. 2. A strong cold front arrives Wednesday night into Thursday morning bringing widespread showers, embedded thunder, and a very low-end severe weather threat. Cooler and drier conditions will spread over the region behind the front on Thursday and Friday. 3. Dry conditions will persist the first half of the weekend before another cold front arrives Sunday into Monday.

DISCUSSION

Key message 1: Scattered showers and isolated thunderstorms possible through the day. Near-record warmth returns today and continues through Wed.

Heights will rise across the area through today...downstream of large scale height falls infiltrating the central part of the country. A broad warm advection regime has become established across the TN Valley into the southern Appalachians this morning, and as a result, an area of convection is moving steadily across east TN. This activity will push into our far western areas through the morning, but will likely weaken as it moves into drier/more stable air across the southern Appalachians...with PoPs increasing to 30- 50% across the mountains of southwest NC and northeast GA.

Coverage of these showers is expected to diminish through the morning, with no worse than partly cloudy skies expected across the entire area by afternoon. With low level moisture steadily increasing on intensifying SW flow, modest destabilization is expected, which should result in isolated/widely scattered showers and some storms. The combo of weak instability and modest shear (~30 kts in the 0-6km layer) should preclude a severe storm threat. Warm frontal activation occurs tonight across the TN and OH Valley alley as a cyclone moves from the Corn Belt into the Great Lakes. Associated showers could brush far western NC...with 20-30 PoPs advertised across the TN border counties.

Under rising height and maturing SW flow, very warm conditions are expected, and the current forecast smashes the daily record of 76 at KAVL, ties the record of 82 at KCLT, and falls just shy of the 84 record at KGSP. The very warm conditions will continue tonight into Wednesday. The current forecast exceeds record warm min temps tonight, and at least ties daily max temp records for Wed.

Key message 2: A strong cold front arrives Wednesday night into Thursday morning bringing widespread showers, embedded thunder, and a very low-end severe weather threat. Cooler and drier con- ditions will spread over the region behind the front on Thursday and Friday.

By Wednesday morning, a remnant cutoff low over western Texas will be interacting with a low-amplitude upper trof extending along the Rocky Mountain front range. The low should begin opening up to the mean flow by late in the day, resulting in an elongated trof axis spanning the entire Mississippi Valley and progged to arrive in the Appalachians by late Wednesday night. At the sfc, a low pressure center will follow the trof axis NE from the lower Midwest into New England thru late Wed night. The associated cold front will approach our fcst area from the NW Wednesday evening. The latest operational model runs continue to trend a bit slower with the progression/approach of the frontal boundary.

Overall, it's still looking like the severe threat will be very limited for our fcst area. Instability is expected to be minimal at best when the front moves thru Thursday morning and when the deeper synoptic forcing is expected to peak. Between roughly 06 and 12z Thursday the models continue to depict a narrow band of up to about 100 J/kg sfc-based CAPE moving out of the mountains and into the NC Piedmont/SC Upstate, paired with roughly 50 to 65 kts of deep layer shear, enough to organize any storms that may develop. Thus, a few isolated storms may develop, and those that do will have the potential to become strong to severe.

Robust, post-frontal CAA will spread over our fcst area beginning Thursday afternoon as the front departs to our east. This will pro- vide a narrow window Thursday aftn/evening for gusty winds across the mtns as well as light NW flow snow showers over the higher peaks and ridges. Any accumulations should be minimal.

Key message 3: Dry conditions will persist the first half of the weekend before another cold front arrives Sunday into Monday.

A weak/dry reinforcing cold front will cross the area on Friday, however the only notable impact on our sensible wx will likely be some gusty winds, mostly over the higher terrain. Thus, we can expect to remain under weak SLY return flow thru the weekend. This will result in the return of at least low-end PoP by Sunday afternoon, confined mainly to the NC mtns, and a warming trend that will persist thru day 7. Rapid cyclogenesis will take place in the lee of the Rockies on Sunday as well. Operational models remain in good agreement that this low will track into the lower Midwest and eventually the Allegheneys by Sunday night, driving another cold front across our area into Monday. The potential for convection associated with this front will depend heavily on its timing and the availability of decent instability and shear. At present, it's still too far in the future to have much confidence regarding the system's severe weather potential.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

At KCLT and elsewhere: VFR conditions are forecast to persist through this forecast cycle. An area of convection over east TN will approach the Terminal Forecast Area this morning. This will most likely weaken before it approaches the TAF sites, but a Prob30 for SHRA begins at 16Z at KAVL. Otherwise, FEW/SCT cumulus in the 045-060 range can be expected later today as the atmosphere becomes unstable. Additional isolated-to-widely scattered showers and possibly a thunderstorm or two will be possible across the area, mainly this afternoon and evening, warranting Prob30s for SHRA at the other NC terminals. TS may need to be added to those Probs in later updates, but coverage is expected to be very isolated at this time. Light SW winds early this morning will increase to around 10 kts at most sites during late morning. Some gusts to near 20 kts are possible during the afternoon, especially at the upstate SC TAF sites. The SW winds will become light again this evening. Increasing moisture will increase the potential for reduced visby early Wed, and will forecast 6SM/BR at several sites. Also can't rule out some low clouds developing, but confidence in this is very low at this time. SW winds will increase to 10-15 kts late Wed morning, with some gusts of over 20 kts expected by early Wed afternoon.

Outlook: Mostly dry conditions linger through Wednesday before SHRA/TSRA chances and associated restrictions return Wednesday night into early Thursday. Gusty winds develop Wednesday into Thursday. Dry conditions return late Thursday into Friday.

CLIMATE

RECORDS FOR 03-10

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 76 1974 29 1932 58 1903 10 1996 1932 KCLT 82 1974 36 1924 59 1903 17 1932 KGSP 84 1974 39 1924 58 2009 17 1932 1997

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.