174 FXUS62 KCHS 112248 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 648 PM EDT Tue May 11 2021 .SYNOPSIS... A cold front will advance into the area tonight then will gradually settle south of the area and stall Wednesday. A series of low pressure areas will track along the stationary front until late week. High pressure will expand into the region this weekend into early next week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... This Evening: Latest radar trends indicate isolated thunderstorms developing upstream and moving into western most areas as well as a few thunderstorms developing along an inland moving seabreeze. A few thunderstorms could become strong and/or briefly severe across inland portions of southeast South Carolina and southeast Georgia this evening given sufficient shear (around 35-40 kt 0-6km bulk shear) and instability (MLCAPE around 1000 J/kg) persisting across the area. DCAPE around 800-1000 J/kg and -10C to -30C CAPE between 300-500 J/kg suggest the main concerns to be strong/damaging wind gusts and moderate size hail for the next few hours, particularly along and west of an inland moving seabreeze where the highest parameter values overlap ahead of a h5 shortwave approaching from the west. Later tonight: A slow-moving cold front will stall over the area. Moisture will steadily increase and PWats are progged to peak over 1.6 inches, which is well above early May climatology. With the front in the vicinity, passing shortwave energy and isentropic ascent, coverage of showers should increase, especially after midnight. There is some instability available ahead of the front, so the forecast maintains mention of thunder. Average rainfall totals through tonight will be between a quarter and half of an inch, highest across the interior. Temperatures will be a bit tricky. The current forecast features lows ranging from the upper 50 across the far northwestern tier to the upper 60s near the Georgia coast. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/... Wednesday: A cold front across far northern areas at the start of the day will surge south and move south of southern zones by evening. Precipitable water values from 1.7 to 1.8 inches in the morning will trend a bit downward Wednesday afternoon and Wednesday night. The combination of the front surging south and decent isentropic lifting developing over top of the shallow air mass, specifically along the 295K and 300K surfaces as depicted very well by the NAM and ECMWF and to a slightly less extent the GFS support likely to categorical POPs across most areas. Pushed POPs up a bit in most areas but further upward trends are quite possible. Highest rain chances are in the morning in the north and during the afternoon in the south. There could be some thunder along and south of the front, especially across southeast Georgia during the late morning and into the afternoon. Temperatures will trend downward during the day across most areas with the highs for the day likely occurring early in the north. As lift subsides and moisture drops off a bit, rain chances will lower Wednesday Night, but still in the high chance category, especially during the evening. Thursday: Models have trended toward keeping more moisture around and the potential for more lift to develop, so have raised rain chances a bit for Thursday, with rain chances quickly dropping off Thursday evening. With extensive cloud cover it will be cool for May with highs in the lower to mid 60s. Friday: Drying will commence and this will allow for some sunshine especially by afternoon. Highs should be in the lower 70s. Lake winds: Strengthening low-level winds and unusually cool air flowing over the warmer waters of Lake Moultrie should promote vigorous mixing/occasional wind gusts as high as 20-25 knots Wednesday through Thursday. Hence have issues a Lake Wind Advisory from 11 AM Wednesday through 11 AM Thursday. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... High pressure and a much drier air mass will build into the region and prevail through early next week. A gradual warming trend will continue through the weekend and by Monday, high temperatures will be back in the mid 70s to mid 80s. Friday night will see low temperatures in the low to mid 50s inland and upper 50s to low 60s just along the coast. Thereafter, each night will see temperatures a few degrees warmer than the previous night. && .AVIATION /20Z TUESDAY THROUGH SUNDAY/... VFR is expected to prevail through the afternoon, then the chance of flight restrictions in showers and low clouds increase overnight. Maintained mention of MVFR for now, though IFR is looking more likely. Sub-VFR conditions will persist through the end of the valid TAF period. Gusty north/northeast winds will develop tomorrow morning, especially at KCHS. Extended Aviation Outlook: Flight restrictions possible through Friday morning during periods of low clouds and showers. && .MARINE... Tonight: A slow moving cold front will remain in the vicinity tonight. Outside thunderstorms that could drift offshore this evening tonight, the pressure gradient doesn't really tighten until right after daybreak, so speeds will average around 10 knots through the night. Seas will average 1 to 2 feet. Wednesday through Sunday: As high pressure moves south into the region and a cold front pushes south of the area, a tightened pressure gradient will enhance NE winds and seas. Then, over the weekend, high pressure will build into the area. A Small Craft Advisory will be in effect for the South Carolina nearshore waters starting Wednesday morning, with Small Craft Advisory for both the nearshore and offshore Georgia waters starting Wednesday afternoon. All of these advisories will be through Friday evening as even if winds drop off a bit seas will remain at least in the 5 to 6 foot range. A Small Craft Advisory for the Charleston Harbor will also begin Wednesday morning and last through Thursday for winds gusting over 25 knots. By Sunday, more ideal marine conditions should return. Rip currents: An elevated risk of rip currents is possible through late week due to gusty northeast winds. && .CLIMATE... An unseasonably cool air mass, accompanied by clouds and showers, could challenge the following record low maximum temperatures Wednesday 5/12 and Thursday 5/13. CHS 5/12 69 (1963) 5/13 68 (1996) CXM 5/12 65 (1907) 5/13 68 (1996) SAV 5/12 69 (1885) 5/13 69 (1928) && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...Lake Wind Advisory from 11 AM Wednesday to 11 AM EDT Thursday for SCZ045. MARINE...Small Craft Advisory from 11 AM Wednesday to 10 PM EDT Friday for AMZ350-352. Small Craft Advisory from 4 PM Wednesday to 10 PM EDT Friday for AMZ354-374. Small Craft Advisory from 11 AM Wednesday to 5 PM EDT Thursday for AMZ330. && $$ NEAR TERM...DPB SHORT TERM...MTE LONG TERM...MTE AVIATION...ETM/MTE MARINE...DPB/MTE CLIMATE...