188 FXUS62 KCHS 160817 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 417 AM EDT Thu May 16 2024 .SYNOPSIS... High pressure will prevail today and persist into Friday. A storm system will affect the area this weekend, followed by high pressure from the north next week. && .NEAR TERM /THROUGH TONIGHT/... Today: Aloft, a longwave trough positioned near the East Coast early this morning will shift further offshore across the western Atlantic, giving way to ridging across the Southeast and Mid- Atlantic states late morning into the afternoon. At the sfc, high pressure will spread across the region, then remain locally for the day. A well defined northwest downslope flow will keep all areas dry across southeast South Carolina and southeast Georgia and support ample sfc heating within sunny/most sunny skies throughout the afternoon. 1000-850mb thickness values support high temps in the mid- upper 80s, with slightly cooler temps at the beaches. Tonight: Quiet weather conditions are expected overnight with sfc high pressure in place and a mid-lvl ridge axis placed across the Southeast United States aloft. Conditions should be favorable for radiational cooling, with winds decoupling early under clear skies and remaining light/calm for several hours away from the immediate coast for much of the night. Late night, some guidance suggests an increase in high clouds from the west, suggesting low temps to occur a few hours prior to daybreak before slightly warming as cloud cover increases aloft. In general, lows should range between the low-mid 60s well inland to upper 60s/lower 70s near the coast. && .SHORT TERM /FRIDAY THROUGH SUNDAY/... Friday: Zonal flow aloft will develop through the daylight hours while a positively tilted mid level trough is positioned over ArkLaTex. At the surface high pressure will retreat out into the Atlantic waters. To the west of the region a low pressure system is forecast to be located in the vicinity of Oklahoma. This feature will slowly progress towards the local forecast area through the day. Generally a quiet weather day is expected across the region, with high temperatures reaching into the mid to upper 80s. Cloud cover will increase throughout the day ahead of the approaching disturbance. By sunset isolated to scattered showers and thunderstorms will be possible across the far inland counties. A warm front is forecast to lift north through the region overnight Friday into Saturday, with PWATs increasing to around 2" by Saturday morning. Precipitation coverage will continue to increase through the overnight hours. Between the rainfall and cloud cover overnight low temperatures will be rather mild, only reaching into the upper 60s far inland with low to mid 70s elsewhere. Saturday and Sunday: Saturday will start with a warm front to the north of the forecast area, putting the region solidly within the warm sector. A cold front will slowly approach from the west, with increasing precipitation chances as the day progresses. Saturday afternoon numerous to widespread showers and thunderstorms will be possible. Both the GFS and ECMWF depict about 1000 J/kg of ML CAPE, which in the presence of 40+ knots of shear could produce a strong to maybe severe thunderstorm on Saturday afternoon. The mid level trough is expected to be rather slow moving and still positioned over the forecast area on Sunday. Models have come into agreement that the an additional surface low pressure system is expected to develop off the NC coastline. A lull in showers and thunderstorms is expected Saturday night, with another round of showers and thunderstorms on Sunday, associated with the low pressure. High temperatures both Saturday and Sunday are forecast to reach into the mid to upper 80s. && .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... By Monday morning the aforementioned mid level trough and associated surface low pressure system will likely be positioned off the NC/SC coastline. Isolated to scattered showers and thunderstorms will be possible, especially along the SC coastal counties. Additionally, with the positioning of the low there is the possibility of a wedge type set up. Some guidance has hinted that high temperatures on Monday may only reach into the upper 70s across southeastern SC. The current forecast does not reflect temperatures this low and instead is a blend showing low to mid 80s. Model trends will need to be watched. After Monday ridging will build in aloft along with high pressure at the surface. Through the middle of the week the forecast features minimal rain chances and warming temperatures, with some locations reaching into the low 90s on Wednesday. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... There could be a period of MVFR cigs due to low stratus for a few hours between 10-14Z Thursday at CHS/JZI terminals, but the probabilities remain too low to include in the latest TAF issuance. Otherwise, expect VFR conditions at CHS/JZI/SAV terminals through 06Z Friday. Extended Aviation Outlook: Showers and thunderstorms could bring flight restrictions to all terminals on Saturday and Sunday as a low pressure system impacts the region. && .MARINE... Today and Tonight: Weak cold air advection in wake of a departing cold front will allow west-northwest winds to gust up to 15-20 kts early morning, but a gradual decrease in wind speeds is expected by mid morning as high pressure settles across local waters and results in the pressure gradient weakening. Winds will gradually turn more southerly this afternoon, remaining around 10-15 kt or less for the rest of the day. Seas will subside throughout the day as well, generally from 2-4 ft to 1-3 ft, remaining largest across offshore Georgia waters and beyond 15 NM from the Charleston County coast. Overnight, conditions remain very quiet across local waters while high pressure prevails. In general, south winds will be no higher than 5-10 kt while seas range between 1-2 ft. Friday through Tuesday: Conditions through the period are expected to remain below Small Craft Advisory criteria. A cold front will push through the region on Saturday, shifting winds more to the W and surging slightly to around 15 knots with gusts to 20 knots. Seas are expected to build on Saturday as well, increasing to 3 to 4 ft. By Monday winds will shift to the NW, generally around 10 knots with seas diminishing to around 1 to 2 ft. High pressure will build in thereafter. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...DPB SHORT TERM...CPM LONG TERM...CPM AVIATION...CPM/DPB MARINE...CPM/DPB