textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Monday afternoon shower chances in the Piedmont have been removed.

KEY MESSAGES

1. A few showers and thunderstorms are possible this afternoon and evening. An isolated severe storm is possible, posing mainly a threat of large hail. 2. Near record warmth on Sunday. A cold front crosses the area Monday afternoon perhaps triggering a few showers. Gusty wind and low relative humidity values give rise to low-end fire weather concerns Monday afternoon. 3. Temperatures returning to values closer to the early Spring normal Tuesday and Wednesday. Unsettled, but generally low- impact, weather continues through the end of the week.

DISCUSSION

Key message 1: A few showers and thunderstorms are possible this afternoon and evening. An isolated severe storm is possible, posing mainly a threat of large hail.

A very ill-defined E-W oriented front is sagging south into the area at AFD time, pushed along by a shortwave aloft moving into the Suthern Appalachians. Moisture attendant with the shortwave collocated with a small area of upper divergence and a weak inversion at about 800mb has led to the development of orographic cirrus across the forecast area. This has kept temperatures running below forecast through the morning, but the cirrus is beginning to erode from the SW and temperatures are responding in kind. With that, still expecting to see well above-normal highs this afternoon, lower to mid 80s across much of the Piedmont, and as the inversion breaks with increased surface heating and afternoon mixing, SBCAPEs and low-level lapse rates will increase. Limited surface/boundary layer moisture will lead to a deep mixed layer with high LCLs, but given the lapse rates as well as the DPVA and lift from the shortwave, isolated severe convection is certainly not out of the question. CAMs remain in general agreement firing convection this afternoon near the TN border and spreading it southeast, but there are still members that want to initiate a separate area of multicell clusters in the Piedmont around peak heating. Convection that develops will work its way SE, with the SPC Marginal Risk outlining this area well. Hail still likely the main threat as best DCAPE remains to our SE a little displaced from the upper forcing, but given the steep lapse rates both wind and hail threats are possible.

Key message 2: Near record warmth on Sunday. A cold front crosses the area Monday afternoon perhaps triggering a few showers. Gusty wind and low relative humidity values give rise to low-end fire weather concerns Monday afternoon.

The combination of rising upper level heights atop the SE CONUS along with an uptick in the llvl WSW flow will promote further warming on Sunday, perhaps maximums reaching the upper 80s in parts of the Piedmont.

Coincident with the approach and passage of a moisture starved cold front, there remains the possibility of late night showers reaching the Tennessee border counties before ashing out later Monday morning. The latest model blend solution with respect to the redevelopment of any deeper convection as the front progress into the Piedmont, is now advertising re-initiation of showers closer to the coastal plain where llvl convergence is slated to increase.

Developing gusty westerly and then northwesterly winds will accompany the aforementioned cold frontal passage. Downslope and post-frontal drying will allow minimum RH values to approach critical level, giving rise to fire weather concern Monday afternoon. We will continue to monitor conditions...

Key message 3: Temperatures returning to values closer to the early Spring normal Tuesday and Wednesday. Unsettled, but generally low- impact, weather continues through the end of the week.

In the wake of Monday's cold frontal passage, cooler sfc ridging and easterly flow looks to develop on Tuesday and linger through Wednesday. During the latter half of the work week within developing llvl southerly flow, weak but steady moisture advection is on tap giving rise to shower chances ramping back up, especially on Friday or Friday night coincident with the approach of the next cold front.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: VFR through the period, except around any lingering showers and thunderstorms this evening. Confidence is increasing that TSRA will not form/impact KCLT, but will hold on to a PROB30 for 01-03z, as convection crosses the mountains and approaches KCLT. Also, with KAVL receiving some rainfall and then light winds overnight, could see some fog form there, so added some MVFR vsby. SW winds will be light overnight, then pick up again Sunday afternoon with gusts in the 15-20 kt range. Plenty of mid and high clouds across the area this evening, should clear out overnight, with generally clear or a few cu Sunday aftn.

Outlook: VFR through midweek. Periodic restrictions with diurnal convection possible later in the week with frontal zone near the area.

CLIMATE

RECORDS FOR 03-21

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 82 1948 34 1960 58 1948 14 1965 1958 KCLT 87 1935 35 1914 65 1912 18 1965 KGSP 88 1907 43 1958 60 1948 18 1965 1906 1927 1906 1921

RECORDS FOR 03-22

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 86 1907 32 1915 58 1991 15 1965 KCLT 89 1907 38 1883 64 1948 24 1965 KGSP 85 1935 42 1985 62 1948 20 1906 1914

GSP WATCHES/WARNINGS/ADVISORIES

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