Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 230602 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 102 AM EST Sat Feb 23 2019 .SYNOPSIS... A high pressure wedge will persist overnight into Saturday. A warm front will lift north through the area Saturday into Saturday evening. A cold front will move offshore Sunday and be followed by high pressure into mid week. Low pressure will impact the area late next week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... As of 1255 AM: Given a nearly saturated BL and broad isentropic lift, rounds of drizzle or mist may pass over the forecast before sunrise. Steady NE will advect lower dewpoints across the SC Lowcountry and portions of SE GA. The wide dewpoint depressions should reduce the fog potential. I will update the forecast to add a mention of drizzle and adjust fog placement and timing. Previous Discussion: Overnight: As a 1034 mb high builds south out of New York state, the resulting cool air damming wedge will persist inland between the coastal plain and the mountains. Considerable low level moisture, the damp grounds and a feed off the Atlantic will result in patchy to areas of fog, some of which will be locally dense. We have expanded the coverage of the fog, mainly over the coastal counties, and also allowed it to persist through the night. Low stratus and a sharp inversion could allow for a little fine drizzle at times as well. Otherwise our best chance of any measurable rain will occur far northwest tier where the best isentropic ascent will occur. Temps won`t fall too much further through the rest of the night, but quite a bit cooler than it was on Friday. Lows will range from the upper 40s and lower 50s northwest to the mid and upper 50s southeast. && .SHORT TERM /6 AM THIS MORNING THROUGH MONDAY/... Saturday: A warm front will lift north through the area during the day into the early evening hours as the inland in-situ wedge beings to break down in response to the transient parent high shifting offshore the Mid-Atlantic states. As is typical with eroding wedges, high temperatures will highly correlated to how quickly the wedge erodes. Generally took a blend of the warmer GFS with the cooler NAM to construct afternoon highs, but there is a big bust potential here in some areas. Highs look to range from the lower-mid 60s for areas adjacent to the southern Midlands and Pee Dee to the upper 70s in the corridor of interior Southeast Georgia bounded by I-16 and I-95. Guidance shows some weak isentropic assent along/ahead of the warm front, but high condensation deficits suggest measurable rainfall is unlikely. Saturday night looks quite warm for late February as strong low-level jetting ahead of an approaching cold front should keep the boundary layer well mixed. Lows will only drop into the lower-mid 60s. Isolated showers are possible overnight as pre-frontal warm air advection/isentropic assent strengthens with the low-level jet. The cold front looks to approach the far western zones by daybreak Sunday. Sunday: A strong cold front is poised to push west-east across the area as its supporting shortwave digs across the Great Lakes and Ohio Valley. Moisture transport along/ahead of the front looks pretty solid with southerly pre-frontal trajectories favoring moisture advection off the Gulf of Mexico. Model cross-sections suggest deep-layered DPVA/omega associated with the passing shortwave and the right entrance region of the upper jet will pass well to the north, but there is strong low-level omega signal from the boundary later to H8 right along the front surface. This suggests lift and associated rainfall will be primary confined to the front itself and should manifest itself by a somewhat broken line of showers moving from west-east during the day. Pops will be confined to 60% area wide for now. Higher pops may eventually be needed, especially across the far interior and the Charleston Tri- County area where the low-level omega signal and moisture transport is the strongest. Highs will warm into the mid-upper 70s with temperatures falling as rain spreads east. Expect clearing and rain- free conditions Sunday Night with lows ranging from the lower 40s well inland to the upper 40s at the coast. Monday: High pressure will extend across the region. It will be considerably cooler with highs ranging from the mid 60s north to upper 60s south; still slightly above climatological normals for most areas. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... Moderate to high confidence through Tuesday with low confidence thereafter. Dry high pressure will likely persist through at least Tuesday before a coastal trough and/or upper disturbance possibly bring a chance of rain back to the forecast through mid week and eventually a low pressure system later in the week. So chances are pretty good that at least a portion of the mid-late week period will be unsettled but timing and rain amounts are quite uncertain. Temperatures should be near to above normal through at least Wednesday before possibly dropping below normal. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... A strong low level inversion and broad weak forcing will maintain IFR to LIFR ceilings across the terminals through the 6Z TAF period. Ceilings may improve to MVFR during the heat of the afternoon, most likely at KSAV. Given a nearly saturated BL and broad forcing, rounds of drizzle or mist may pass over the terminals prior to sunrise. A warm front is expected to lift across the region tonight, resulting in winds to shift from the SE. Ceilings should gradually lower in the wake of the warm front, the potential for fog will be greater after the 6Z TAF window. Extended Aviation Outlook: Restrictions likely Saturday night into Sunday afternoon at KCHS/KSAV. Strong winds also possible Sunday. More restrictions possible toward the middle of next week. && .MARINE... Overnight: The modest NE pinching persists between an inland wedge and the backdoor cold front south of the local waters and continuing its trek southward. We have maintained a marginal Small Craft Advisory (SCA) for the AMZ350 waters, and just below SCA`s elsewhere. Fog and low stratus will be a continued problem for mariners, resulting in areas of visibilities less than 1 nm on the Georgia and lower South Carolina waters, with pockets of visibility even lower. On the northern South Carolina waters and in Charleston harbor we expect patchy fog with 1 to 3 nm visibility to occur. There is probably too much wind for a Dense Fog Advisory. Saturday through Monday: Solid northeast winds Saturday morning will gradually veer southerly through the day as a warm front lifts north. Southwest winds will increase to 15-20 kt Saturday night as pre-frontal low-level jetting intensifies. Cool shelf waters will limit winds, especially over the Georgia nearshore waters. By Sunday, winds and seas look to reach marginal Small Craft Advisory thresholds over the Georgia offshore and Charleston County legs with winds 20-25 kt and Seas 4-6 ft, while the other legs look to fall just below this. Winds will veer west and eventually northwest Sunday afternoon and Sunday night behind the cold front. Could see some patchy sea fog develop Saturday afternoon across the Georgia waters and spread into the South Carolina waters Saturday Night. Winds look to be a bit too strong Saturday night to support widespread development, but this will have to be watched. If any sea fog develops, it will likely linger in some fashion until FROPA Sunday afternoon. Benign weather will prevail Monday through Wednesday. && .CLIMATE... Record Highs for February 24... KCHS: 81/2017 and previous KCXM: 81/1930 KSAV: 86/2012 Record High Mins for February 24... KCHS: 60/1992 and previous KCXM: 63/2018 KSAV: 64/1980 && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...Small Craft Advisory until 4 AM EST early this morning for AMZ350. && $$ NEAR TERM...NED SHORT TERM...ST LONG TERM...RJB AVIATION...NED MARINE... CLIMATE...

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