010 FXUS62 KCHS 201055 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 655 AM EDT Mon Apr 20 2020 .SYNOPSIS... A warm front will lift north through the area early this morning followed by a cold front later this morning. High pressure will then slowly build in through Wednesday before another storm system impacts the area Thursday and Thursday night. Unsettled weather could then return over the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 650 AM: I will update the forecast to remove all zones but the outer waters from Tornado Watch 126. In addition, the Flash Flood Watch has been cancelled. The band of strong to severe thunderstorms should move beyond the outer waters over the next hour. As of 545 AM: I will update the forecast to remove a western tier of counties from Tornado Watch 126. The strong to severe thunderstorms should push solidly over the waters over the next hour. As of 415 AM: Latest SPC mesoanalysis and sfc observations indicated that the warm front was pushing west across the coastal counties. MLCAPE south and east of the front has increased to 500-1000 J/kg. KCLX detected taller cells with meso, these storms should push over the Altamaha River through 430 AM. To the west, a line of strong to severe storms and an associated cold pool was on track to push across the SE GA and lower SC during the pre-dawn hours. These storms will remain in a well sheared environment, effective bulk shear of 55-60 kts. Storm structure may increase as they move east toward the coast, reaching the warm front, encountering increasing shear and instability. Tornado Watch 126 will remain across most of the forecast area until 11 AM. These storms will push across inland GA, which has seen bands of 3-4 inches of rain fall since Sunday afternoon. In addition, storm motions are expected to parallel the coast early this morning. With high tide around 7 AM, coastal areas will be watched closely for flooding. Flash Flood Watch in effect until noon. See Hydrology section below for additional details. The storms are expected to push offshore this morning, followed by a cold front. Gust WNW winds will develop in the wake of the front, remaining gusty through this afternoon. High pressure will build across the region this evening and overnight. Winds should become light during the evening, then light to calm tonight. Low temperatures are forecast to fall into the mid 50s to around 60. && .SHORT TERM /TUESDAY THROUGH THURSDAY/... High confidence this period. Deep troughing will linger across the area Tuesday with a dry cold front to move through Tuesday night. High pressure will then move in for Wednesday before quickly shifting offshore Wednesday night as another storm system approaches from the west. There could be a few showers Wednesday night due to warm advection and shortwave energy aloft, but the surface warm front will likely not push north through the area until later Thursday morning as low-level jetting ramps up ahead of the developing surface low over the TN Valley. Surface winds even outside any storms could be rather strong. Deep moisture and strong upper forcing should support a good rain event with several inches possible along with at least a slight chance of severe storms Thursday afternoon into the evening due to plentiful deep and low- level shear and modest instability. Near to above normal temperatures are expected except for Wednesday when it should be below normal. && .LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/... Moderate confidence Thursday night with low confidence thereafter. Expect the potential for some severe storms into Thursday evening before a cold front pushes through. Weak high pressure should prevail with dry weather Friday but the forecast gets more complicated thereafter given several disturbances in the fast upper flow that could impact the area through the weekend. Temperatures should be above normal until possibly falling back below normal early next week. && .AVIATION /12Z MONDAY THROUGH FRIDAY/... Prior to the 6Z TAFs, KCLX detected widespread showers across the forecast area with stronger updrafts across SE GA. The sfc warm front was analyzed along and near the SC and GA coast, very close to KCHS. Ceilings near the front were IFR, KCHS is expected to maintain IFR ceilings and MVFR vis until sunrise. KSAV remained a bit west and north of the warm front early this morning, supporting MVFR ceilings. Ongoing severe thunderstorms over southern GA are timed to pass over KSAV between 8-10Z and KCHS 12-14Z, highlighted with a TEMPO. In the wake of the convection and passage of a cold front, WNW winds should gusts between 20-25 kts through this afternoon. Extended Aviation Outlook: High confidence in VFR until restrictions likely return as early as late Wednesday night but most likely Thursday and Thursday night as another storm system impacts the area with strong winds and possible severe storms. VFR should return Friday but more restrictions are possible Saturday as a cold front could impact the area. && .MARINE... Today and tonight: The pressure gradient ahead of a cold front will support gusty SW winds across the waters this morning. Forecast soundings indicate gusts between 35-40 kts. Gale Warning in effect until noon for all zones, except AMZ354 and 330 with Small Craft Advisories. Severe thunderstorms will likely push over or develop over the waters this morning, producing severe winds or waterspouts. Conditions will improve steadily this evening as high pressure builds east over the region. Tonight, ridging high pressure will yield light winds and seas of 2-3 ft. Tuesday through Saturday: Moderate to high confidence this period. There are no significant concerns through Wednesday night, although conditions could reach marginal Small Craft Advisory levels Tuesday afternoon along the Charleston County coast as the gradient pinches ahead of an approaching cold front. A better chance for Small Craft Advisory/possible Gale conditions are expected Thursday into Friday as yet another potent storm system affects the area. Low confidence of more SCA conditions Saturday depending on whether another cold front impacts the area. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...Small Craft Advisory until noon EDT today for AMZ330-354. Gale Warning until noon EDT today for AMZ350-352-374. && $$ NEAR TERM...NED SHORT TERM...RJB LONG TERM...RJB AVIATION...NED/RJB MARINE...NED/RJB