Sunrise 6:35 AM   Sunset 8:18 PM Moonrise 3:03 AM   Moonset 2:27 PM

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FXUS62 KGSP 031038 AFDGSP

Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 638 AM EDT Fri May 3 2024

SYNOPSIS
Dry and warm high pressure moves off the Carolina coast as a front approaches from the west then stalls over our region for the weekend. This front will result in periodic thunderstorms and showers starting today and lingering through the weekend. A general summertime pattern sets up early next week, which will likely support scattered thunderstorm development each afternoon.

NEAR TERM /THROUGH TONIGHT/
As of 630 am EDT Friday: Height falls will impact the East through the near term, with associated slow-moving/zonally-oriented frontal zone expected to sag toward our forecast area later today into tonight
Deep layer lift
albeit relatively weak...will approach the CWA late today into tonight, while SW flow will result in increasing levels of moisture, with forecast soundings indicating precipitable waters will be in the ~90th percentile category for the day. Therefore, conditions will become increasingly favorable for convective development as the day progresses. Scattered showers are already covering much of north GA and east TN this morning, and some of these appear poised to move over portions of our GA counties as well as far SW NC through the morning, warranting steadily increasing PoPs in those areas over the next 2-6 hours.

Otherwise, high and mid level clouds will continue to increase through the morning...resulting in cooler conditions than on Thursday, while mid-level lapse rates are forecast to be poor. As such, surface-based instability will be quite tame at 1000-1500 J/kg of CAPE this afternoon. Meanwhile, wind shear parameters will be very unremarkable, with 0-6km bulk shear ~20 kts. So, the conditional probability of severe storms is about as close to 0 as it gets. There could be locally heavy rainfall with deeper cells and/or if an area of training cells manages to materialize. However, dry antecedent conditions should preclude a notable excessive rainfall threat.

While a general decrease in coverage and intensity of convection is expected this evening, high moisture content combined with continued modest lift is expected to result in scattered convection (primarily showers) persisting well into the overnight, with perhaps a locally heavy rainfall event or two possible. Temps will be 5-10 degrees above climo through the period.

SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/
As of 300 AM EDT Friday: Upper ridging will remain over the East Coast on Saturday before gradually pushing east into the western Atlantic Saturday night into Sunday. At the sfc the forecast area will be caught in-between two sfc highs (one over New England/SE Canada and one over the Northern Plains/Upper Midwest) as a cold front slowly approaches out of the west. The front should remain north and west of the forecast area Sunday into Sunday night. This messy pattern will lead to 850 mb S/SW'ly flow allowing for an influx of Gulf moisture across Southeast through the weekend, leading to scattered to widespread showers and thunderstorms each day. Went with likely to categorical PoPs Saturday through early Sunday evening and chance PoPs Sunday night. With PWATs expected to climb well above climo (~1.6 inches east of the mtns and ~1.3 inches across the mtns) and weak shear (~10-15 kts) leading to slow storm motion, heavy rainfall will accompany shower and thunderstorm activity. However, the overall threat for flash flooding looks to remain low due to dry antecedent conditions. Nuisance flooding cannot be entirely ruled out, especially for areas that see heavy rainfall repeatedly track over the same locations. SBCAPE looks to range from ~700-1500 J/kg each afternoon per the HRRR, GFS, Canadian and ECMWF. The NAM and NAMNest are much more bullish regarding SBCAPE through the weekend but this looks overdone as widespread cloud cover from the influx of Gulf moisture should limit destabilization somewhat. Thus, the severe potential looks rather low through the weekend thanks to the low wind shear and increased cloud cover. The SPC Day 2 and 3 Severe Weather Outlooks have the GSP forecast area in a general thunder risk which looks reasonable at this time. However, a few strong storms cannot be entirely ruled out, especially for any areas that see breaks in cloud cover. Highs on Saturday will end up near climo to a few degrees below climo thanks to SSE'ly sfc winds, convection and cloud cover. Highs on Sunday will climb to around 3-5 degrees above climo thanks to sfc winds turning more S/SSW. Lows through the short term will end up around 10-13 degrees above climo thanks to clouds limiting radiational cooling.

LONG TERM /MONDAY THROUGH THURSDAY/
As of 330 AM EDT Friday: The workweek will kick off similar to the weekend as the aforementioned cold front remains stalled over the Lower Midwest/Ohio Valley region. This will allow for another round of scattered to widespread showers and thunderstorms on Monday.
Despite SBCAPE looking slightly higher on Monday compared to the weekend, widespread cloud cover and weak shear should linger, allowing the severe weather threat to remain low. Highs on Monday will be similar to Sunday's, ending up around 3-5 degrees above climo. Lows Monday night will remain around 10-12 degrees above climo thanks to some lingering cloud cover. Drier conditions may return for most of the forecast area, with the exception of the NC/TN border, Tuesday through early Thursday as the stalled front gradually lifts northward across the Ohio Valley/eastern Great Lakes region. Convective chances increase again late Thursday into Friday as an upper low approaches out of the northwest. Highs should climb into the mid to upper 80s Tuesday through Friday, which is around 7- 12 degrees above climo. Lows should remain around 10-12 degrees above climo through the long term.

AVIATION /12Z FRIDAY THROUGH TUESDAY/
At KCLT and elsewhere: VFR conditions are expected to persist across the Terminal Forecast Area through the day, with steadily increasing high/mid clouds expected. An upper level disturbance and associated moisture plume will approach the area throughout the day, allowing for expansion of showers and thunderstorms, mainly during the afternoon and evening. However, scattered showers are already amassing just upstream of the area across north GA and east TN. Some of these initial SHRA could brush past the upstate SC terminals and KAVL later this morning, but the better chances should hold off until this afternoon. Scattered coverage of convection is expected this pm
at least across the western half of the area
warranting Prob30s for -TSRA at most sites during the afternoon/early evening.
Current indications are that instability will decrease toward the east, so thunder is omitted from the KCLT TAF for the time being.

While some diminishment of convective coverage is expected this evening...showers will remain possible well into the overnight hours/early Saturday. A consensus of high resolution guidance suggests another period of scattered showers circa 12Z Sat, so most TAFs receive another Prob30 (for SHRA) during that time frame.
Chances for restrictions in fog/stratus will also increase toward sunrise Sat, and MVFR conditions are included at all sites. Winds will generally be calm or light/variable early this morning, becoming SW at 5-10 kts by afternoon.

Outlook: Enhanced moisture will combine with a weak/stalled front through early next week, resulting in a period of active/mainly diurnal convective weather each day. There will also be the potential for restrictions associated with widespread fog and/or low clouds each morning.

GSP WATCHES/WARNINGS/ADVISORIES
GA...None.
NC...None.
SC...None.

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