textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

A Special Weather Statement for patchy dense fog has been issued for our non-mountain zones. If the fog becomes more widespread, a Dense Fog Advisory may be needed.

Updated the aviation discussion for the 06z TAFs.

Confidence is increasing that a strong cold front will bring a band of rain showers with isolated embedded thunderstorms followed by a significant air mass change Wed night/Thursday.

KEY MESSAGES

1. Areas of fog and low stratus are expected across our area this morning. The fog could become dense and will likely linger well into the morning. Otherwise, drier conditions are expected today with temperatures remaining well-above normal for early March. 2. Near-record warmth returns on Tuesday and Wednesday, with scattered showers and thunderstorms expected Tuesday. 3. A strong cold front arrives Wednesday night producing widespread showers, isolated thunderstorms and perhaps a low end severe weather threat. Much cooler and drier weather develops behind the front for Thu and Fri.

DISCUSSION

Key message 1: Areas of fog and low stratus are expected across our area this morning. The fog could become dense and will likely linger well into the morning. Otherwise, drier conditions are expected today with temperatures remaining well-above normal for early March.

Light to calm winds and a moist boundary layer will create an ideal environment for low stratus and fog to develop across our area over- night. In general, the eastern SC Upstate and NC Piedmont still appear more likely to see widespread dense fog, however we're already seeing sites in the western Upstate and NC mountain valleys with reduced vis- ibilities. A Special Weather Statement for patchy fog has been issued for all of our non-mtn zones. If the fog becomes more widespread, a Dense Fog Advisory will likely be needed. With winds remaining light and low clouds expected to linger thru most of the morning, any fog will likely not burn off until late morning for most locations.

Otherwise, once the morning fog/stratus dissipates, temperatures will rebound into the mid to upper 70s across the lower elevations, ending up 15+ degrees above normal. Nonetheless, the highs will still likely fall short of daily records at our climate sites.

Key message 2: Near-record warmth returns on Tuesday and Wednesday, with scattered showers and thunderstorms expected Tuesday.

A split upper air pattern will be in place atop the country through mid-week, with amplification occurring in the northern stream in response to northwestern Conus height falls...while the southern stream will be dominated by an upper low kicking from the Four Corners into Texas. For Tuesday, low level trajectories originating from the Gulf will ensure elevated moisture levels supporting at least modest levels of instability. Scattered showers and perhaps a storm or two may be ongoing Tue morning, as a dampening short wave trough passes over the region within broader area of height rises. This feature will pass east of our area by afternoon, but additional isolated or widely scattered development is possible during the afternoon within the unstable environment. Deep layer shear of 30-40 kts won't be especially conducive to organized convection given the expected limited instability, but a stray severe storm can't be ruled out.

The bigger story for the mid-week period will be the return of record, or at least near-record warmth, as heights rise and a muggy warm sector regime becomes re-established. The current max temp forecast for Tue is just a degree shy of daily records at KCLT and KGSP, and would break the record at KAVL by a couple of degrees. For Wed, the current forecast exceeds daily records at KCLT and KAVL, and is within a degree of the record at KGSP. Record warm min temps are also likely to be broken Tue night.

Key message 3: A strong cold front arrives Wednesday night producing widespread showers, isolated thunderstorms and perhaps a low end severe weather threat. Much cooler and drier weather develops behind the front for Thu and Fri.

A weakening upper low in the southern stream of a split flow regime will move from Texas into the Deep South Wed night, as a strong northern stream wave will be digging across the Great Lakes and the Ohio Valley...with phasing of the two streams expected over the East on Thursday. Associated strong frontal zone is forecast to move into the forecast area between 06-12Z Thursday, warranting likely-to-categorical PoPs across the entire area from late Wed night through Thu morning. Strong moisture flux will be in place off the Gulf in advance of the front, which combined with warm/well-mixed conditions could maintain a ribbon of weak surface-based instability immediately ahead of the front. The Global models continue to depict a narrow zone of focused ascent along the leading edge of the front, which could interact with the weak instability to produce a low-topped quasi-linear convective system. Limiting factors for an organized severe storm threat are due to the delayed phasing of the upper air pattern...which may not be completed until the upper trough is east of the forecast area. This results in forcing not being as deep and strong as one would usually like to see for low CAPE environments. Additionally, low-level flow will be veered and large unidirectional...resulting in 0-1km shear values of 25-30 kts...strong, but not the 35+ kts that we typically need for anything more than a marginal threat in weakly unstable situations. Nevertheless, the forecast pattern and ingredients will be adequate for a low-end threat.

Strong cold advection will overspread the area during the daylight hours Thursday, and the high elevations may see a transition to a brief period of snow or a rain/snow mix before the precip ends...and even some light accums are possible above 3500 feet or so. Temperatures will return to levels more sane for late winter Thu-Fri, but that will be short-lived as return flow sets up and height rise over the region...downstream of more western Conus height falls. As a result, temps quickly to well-above normal levels over the weekend...although conditions will remain dry as moisture will be slower to increase.

AVIATION /07Z MONDAY THROUGH FRIDAY/

At KCLT and elsewhere: Expect dry, VFR conditions thru most of the 06z TAF period outside of patchy dense fog and low stratus overnight and well into the morning. Conditions have already deteriorated at numerous sites across our area, with a handful of terminals already reporting 1/4 SM and FG. KCLT and KHKY still appear most likely to see LIFR and/or VLIFR thru the morning, but there's a decent chance that the Upstate terminals and KAVL will see similar restrictions. Any restrictions are likely to linger thru most of the morning as winds will remain light to calm and it will take some time for daytime heating to have a substantial impact. Expect all sites to return to VFR by 14 to 15z. Otherwise, winds will be light to calm overnight and well into the morning. Outside the mtns, they will pick up from the WSW/SW during the afternoon with speeds between 5 and 10 kts. At KAVL, winds will remain light today and generally favor a NWLY direction this aftn.

Outlook: The spring-like weather pattern will linger for the next few days with patchy fog/low stratus possible each morning. Isolated TSRA may return Tues with better TSRA chances expected Wed night into early Thurs. Gusty winds will develop Wed into Thurs across the area as well. Drier conditions return late Thurs into Fri.

CLIMATE

RECORDS FOR 03-09

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 80 1974 22 1932 57 1964 8 1996 KCLT 83 2009 30 1960 62 1925 16 1996 1974 1921 1925 KGSP 85 2009 29 1960 60 2009 16 1996 1921

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.