Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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093 FXUS62 KCHS 091757 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 157 PM EDT Thu May 9 2024 .SYNOPSIS... A cold front will approach the area tonight, then move offshore Friday. High pressure will prevail for the weekend into early next week. A storm system could affect the area by the middle of next week. && .NEAR TERM /THROUGH TONIGHT/... Radar indicates a line of strong to severe thunderstorms over our area and moving towards the coast. Temperatures ahead of the line have peaked in the mid to upper 80s, which is a bit lower than the expected highs, owing partially to stratus hanging around a little longer this morning. But even with this, there is plenty of instability in place. SPC Mesoscale Analysis indicates MLCAPE values peaking in the 1,500-2,000 J/kg with effective bulk shear 45-50 kt. DCAPE values have trended a little lower, but combined with the shear, this will continue to bring us an enhanced wind threat. An tornado also cannot be ruled out into late this afternoon given the hodographs. We continue to adjust the POPs/weather grids based on the radar trends. The CAMs continue to indicate the southern end of the line that will move across our GA counties will be slower to reach the coast by about 1-2 hours, followed by stratiform precipitation across our area for about 1-2 hours beyond that. The rainfall will dissipate and move east of the forecast area by mid-evening. The rest of the night should remain generally dry. However, a second MCS will arrive from the west after the pre- dawn hours Friday morning. Rain-cooled temperatures are expected to remain nearly steady around 70 degrees tonight. && .SHORT TERM /FRIDAY THROUGH SUNDAY/... Friday: We remain focused on Friday with another potential severe weather day ahead. By morning, the cold front will be positioned across the SC/GA Midlands. The front is not expected to clear the area until late, therefore we could see another round of convection moving in from the west some time between late morning and afternoon as the boundary presses toward the coast. This is another highly uncertain event with a range of possibilities, noted by differing solutions for nearly each model. Most models do show some sort of line/cluster of showers and thunderstorms moving through the forecast area at some point during the day however. One possibility is that lingering showers/thunderstorms in the morning could delay destabilization, which will inhibit deep convection later in the afternoon. There are also signals of an upstream MCV propagating across southern AL/GA and northern FL, which could advance into southeast Georgia and portions of southeast South Carolina. However these southerly systems have the potential to greatly alter the downstream environment by cutting off southerly flow/moisture across the forecast area, thus inhibiting destabilization. On the other hand, a moderate break from the previous night`s convection and perhaps a slight break in clouds would destabilize the environment early on, allowing for a rich, untapped environment for strong/severe storms to develop. Overall, it is unclear how the severe threat will pan out Friday, and there is a degree of dependence on the evolution of Thursday`s event. With that said, any severe storms that develop would be capable of producing damaging wind gusts, large hail, and/or an isolated tornado. Outside of severe weather, showers and even general thunderstorms could result in locally heavy downpours with PWATS in the 1.6-1.8" range. Guidance hints towards the greatest rainfall amounts falling south of the Savannah River. Showers and thunderstorms should push offshore by the evening with conditions rapidly clearing behind the front. Max temperatures will be slightly cooler due to ongoing or afternoon convection, with highs in the mid 80s. FROPA and clearing skies will cause temperatures to significantly drop Friday night, with lows in the mid to upper 50s inland and lower 60s along the coast. Saturday and Sunday: Quasi-zonal flow will exist aloft and general high pressure will gradually build. A cool, dry air mass will move into the area behind the cold front bringing rain-free conditions. Mostly sunny skies are expected both days with highs peaking in the upper 70s to low 80s Saturday and low to mid 80s Sunday. A relatively cool night is expected Saturday, with lows in the mid to upper 50s inland and lower 60s along the coast. && .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... Early next week will briefly start off quiet before a warm front extending across the Deep South lifts north. Conditions look quite unsettled beginning late Monday night into Wednesday. Rain chances were increased into the likely range (55-70%) during this period due to the consensus of deep moisture moving in, in addition to plentiful forcing aloft with a shortwave traversing the Central U.S. Near normal temperatures are expected to rise through the middle of next week owing to southerly flow. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... 18z TAFs: Radar indicates a line of thunderstorms moving towards the coast. The highest probability of impacts is noted with TEMPO groups, with remnant thunderstorms persisting afterwards, and then stratiform precipitation. The precipitation should end by this evening, with VFR persisting into part of the night. MOS and some of the ensembles then indicate IFR ceilings developing over the terminals late tonight, which we kept in the TAFs. Finally, another round of showers and thunderstorms is expected to bring impacts to the TAF sites late in the TAF time period. Extended Aviation Outlook: Scattered to numerous showers and thunderstorms could continue into Friday afternoon with flight restrictions and gusty winds possible within convection. VFR conditions will return for the weekend into early next week. && .MARINE... Southwest winds will range between 15-20 kt the rest of this afternoon. A few periods of gusts around 25 kt are possible across the Charleston County nearshore waters, but no Small Craft Advisories are planned at this time. Seas should favor values between 3-4 ft, with 5 ft seas possible across portions of the Charleston Co. nearshore. Otherwise, the primary concern remains the passage of a squall line of thunderstorms late this afternoon into early this evening. These storms could produce gusts in excess of 50 kts and possibly a waterspout. Convection should end over the marine zones this evening. Winds tonight will return from the southwest between 15 to 20 kts. Wave heights of 2-4 ft will be common tonight. Friday: A strong cold front will push offshore late, causing SW winds to shift out of the north. Marginal Small Craft Advisory conditions are expected Friday afternoon through Friday night with gusts ranging between 20-25 kt. At this time, the Charleston County nearshore waters out to 20nm and the outer Georgia waters from 20- 60nm look the most promising for any advisories that could be needed. Seas will be slightly elevated with 2-4 ft in the nearshore waters and 5 ft seas beyond 20nm. Another concern for the local waters will be the potential for strong thunderstorms Friday afternoon. There is still a large degree of uncertainty; however, any storms that do develop and move across the waters will be capable of producing strong wind gusts. Saturday through Tuesday: Marine conditions will improve Saturday morning as high pressure builds in from the west. Northerly winds will shift out of the south with speeds dropping to 10 kt or less and seas averaging 1-3 ft through Monday. Monday night into Tuesday winds and seas look to increase/build ahead of the next storm system. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM... SHORT TERM...BRM LONG TERM...BRM AVIATION...BRM MARINE...BRM