Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 252335 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 735 PM EDT Tue Jul 25 2017 .SYNOPSIS... Broad low pressure will remain across the Carolinas and Georgia through tonight. A weak cold front will then stall over or near southeast South Carolina through Thursday. Another cold front will move into the area this weekend and stall into early next week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... As of 725 pm: At the top of the hour, an automated raingauge at Midville, GA indicated that 3.11 inches of rain fall in one hour. At this time, a multi-cell thunderstorm over McIntosh was producing torrential rainfall rates that ranged close to what was observed at Midville. In addition, a line of thunderstorms should drift north across the Altamaha River Valley, likely raining out and becoming stratiform rain by 10 pm. Elsewhere, light stratiform rain should continue or areas that are dry will remain dry overnight. However, there is a chance that convection may approach Berkeley County form the north. I will update the forecast to reflect the latest radar trends and thinking. Previous Discussion: To start, ahead of an upper low advancing east across southern GA, thunderstorm coverage will range from numerous/widespread across SE GA to isolated/scattered across SE SC into early evening. Primary concerns focus on the threat for locally excessive rainfall within an environment featuring PWATs exceeding 2 inches and weak steering flow, especially where coverage is maximized across SE GA. MLCapes exceeding 2000 j/kg could translate to an isolated/brief pulse severe event with damaging wind gusts, but the probability for severe weather will remain low. Thunderstorms should undergo diurnal weakening/dissipation later this evening. Then, as the upper low continues to roll toward the region, isolated/scattered showers/thunderstorms could redevelop later tonight. Locally heavy rain could again occur, especially along the coast. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/... Troughing will linger through the period, although it will be strongest through Thursday. The deepest moisture is also likely through Thursday so through this time is when we expect the highest rain chances, especially Wednesday. Although cannot rule out isolated severe storms, the bigger risk will be heavy rainfall/flooding given weak wind fields and very deep moisture. This wetter than normal pattern will lead to lower than normal high temperatures and generally above normal low temperatures. By Friday temperatures could reach above normal in the mid 90s with heat index values peaking in the lower 100s. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... Deep moisture will advect to the Southeast United States ahead of a cold front that is expected to move into the area Saturday. PWATs between 2.25 to 2.5 inches and forcing associated with the front support numerous showers and thunderstorms Saturday into Sunday while the front slowly progresses south and eventually stalls over or near southern areas of Southeast Georgia. A few thunderstorms could become more organized than previous days given greater wind fields aloft, but the overall threat of stronger thunderstorms could be limited due to the timing of fropa during earlier hours on Saturday. At least chances of showers and thunderstorms could linger into early next week while moisture continues to lift over or near the stationary front. Temps will generally be a few degrees below normal this weekend and early next week given extensive cloud cover and precip activity. In general, temps should peak in the mid/upper 80s. Overnight lows will range in the low/mid 70s. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... Thunderstorms are expected this afternoon at both terminals, with most significant impacts at KSAV. Then, VFR conditions are forecast at both terminals through the 18Z TAF cycle. However, low-level moisture could support MVFR/IFR ceilings later tonight. Then, as an upper level low advances east and deep- layered moisture spreads north across the region, showers could redevelop late tonight, and thunderstorms could develop before the end of the 18Z TAF period. Any showers/ thunderstorms could produce flight restrictions. Extended Aviation Outlook: Brief flight restrictions are possible with showers and thunderstorms, especially Wednesday into Thursday as weak low pressure approaches the region. VFR conditions should prevail late Thursday and Friday before flight restrictions return with showers and thunderstorms along/near another cold front Saturday. && .MARINE... Seas of 2-3 feet will persist through tonight. The sea breeze and synoptic winds will combine to produce S/SW winds 10-15 knots into early evening, then synoptic SW winds mainly 15 kt or less will prevail for the remainder of tonight. Thunderstorms could produce locally hazardous conditions over GA waters this afternoon/evening and anywhere across the coastal waters later tonight. Wednesday through Sunday: A cold front looks to stall near the SC waters through Thursday before dissipating before another cold front moves into the area this weekend. Conditions are expected to remain below Small Craft Advisory levels through the period. However, a southwest/south flow could gust around 20 knots Friday night into early Saturday until cold fropa occurs. Seas will gradually build from 2-3 ft up to 4 ft at times later this week as the pressure gradient tightens a bit ahead of the front. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...NED/SPR SHORT TERM...RJB LONG TERM...DPB AVIATION...RJB/SPR MARINE...RJB/SPR is the U.S. government's official web portal to all federal, state and local government web resources and services.