697 FXUS62 KCHS 291804 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 104 PM EST Sat Feb 29 2020 .SYNOPSIS... High pressure will extend across the region through Tuesday. A cold front could bring impacts to the region during the middle of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... No major changes with the latest update. Surface high pressure to the west will build into the area as a deep upper trough across the eastern U.S. shifts offshore. The colder air aloft associated with the trough will lead to some cumulus this afternoon, especially in SC. Highs should reach near 60 most locales, although could stay in the mid 50s near the Pee Dee/Midlands where the most cloud cover is expected. Deep mixing of stronger winds aloft will support a breezy day with winds about 15-20 mph and gusts 25-30 mph. Lake Winds: West to northwest winds will remain strong over Lake Moultrie, reaching 15-20 kt. There could be some gusts near 25 kt but we didn't think it warranted a Lake Wind Advisory at this time given the low confidence of high enough speeds/duration. && .SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/... Tonight: High pressure will settle directly over the region as mid-level heights slowly rise through the night. The boundary layer is expected to decouple later in the evening with winds going calm to light for most areas. Clear skies, calm winds and dewpoints in the lower-mid 20s will support strong radiational cooling away from bodies of water with lows poised to drop into the upper 20s/lower 30s inland, lower-mid 30s at the coast with upper 30s/near 40 at the beaches, Downtown Charleston, and areas immediate adjacent to the Santee-Cooper lakes. The freezing line looks to setup roughly along US-17 in south coastal South Carolina and I-95 in coastal Georgia, including parts of the Savannah and Charleston Metro Areas. The local growing season begins on 1 March, so a Freeze Watch has been posted for all but the Georgia coastal zones. Freeze durations will range from 3-6 hours far inland to 1-2 hours near the above mentioned freezing line. Although dewpoints depressions will remain somewhat elevated, soil moisture levels remain quite high and will support the formation of scattered to widespread frost for many areas away from the coast. Sunday: A weak, mid-level ridge will move over the East coast later in the day, then move offshore overnight. Surface high pressure centered overhead in the morning will shift offshore during the afternoon and gradually move away overnight. Plenty of subsidence is in place, leading to a dry and mostly sunny forecast. The combination of mostly sunny skies, warmer 850 mb temperatures, and S to SW surface winds will moderate the airmass. High temperatures will generally be in the 60s. Monday: The mid-levels will consist of zonal flow. At the surface, high pressure offshore is forecasted to move away. During the afternoon, a weak surface trough is expected to form just to our east, causing some showers, Though, most of the models keep these showers over the coastal waters during the afternoon and into the night. Meanwhile, a cold front will be to our distant west, slowly approaching. The models indicate some showers ahead of this front could make it into our western areas during the afternoon and into the night. But they should be light with very little, if any QPF. Hence, we're only going slight chance POPs. Essentially, most locations should be dry a majority of the time. Warmer temperatures are expected within the S to SW surface winds. Highs should be around 70 degrees. Lows should be in the 50s. Tuesday: Mid-level zonal flow should prevail with heights gradually rising. A weak surface trough will remain to our east while a cold front approaches from the west. While the models keep any showers associated with the trough far offshore, they disagree on the precipitation potential from the approaching front. Some indicate it'll be mostly dry while others have decent QPF for us. Since a majority generally have us within the dry slot, and this has been the trend for the past few days, we opted to go this route. Slight chance POPs are limited to far inland. The noticeable change will be the high temperatures. Despite increasing clouds, 850 mb temperatures and thickness values support temperatures into the upper 70s to near 80 degrees. Though, it'll be much cooler at the beaches due to the slightly onshore winds. It'll also be breezy for most locations, especially in the afternoon. && .LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/... The 00Z models still differ quite a bit during the long term. They range from having the front quickly moving through Wednesday night, to hanging around into Thursday or even Thursday night. We trended in the slower direction, but expect more changes will be needed with future forecasts. There remains the concern for severe weather with the front. But this will depend largely on if multiple variables are able to come together. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... VFR at KCHS/KSAV through the 18Z TAF period. Only concern is gusty winds near 25 kt, mainly through about 22Z. Extended Aviation Outlook: Flight restrictions are possible ahead of a cold front Tuesday night into Wednesday. Also, it'll be breezy Tuesday and Wednesday. && .MARINE... Today: Elevated winds will persist across the waters today as cold air advection lingers as shortwave energy passes by. West to northwest winds of 15-20 kt with gusts to 25 kt are expected across the nearshore waters, including Charleston Harbor, with 20-25 kt with gusts to 30 kt over the Georgia offshore leg. Small Craft Advisories remain in force for these areas. Offshore winds will limit wave growth with max significant wave heights ranging from 2-4 ft nearshore (1-2 ft near the immediate coast) with 4-6 ft over the Georgia offshore waters. Tonight: Winds and seas will rapidly diminish as high pressure builds in from the west. Conditions look to drop below Small Craft Advisory thresholds by late evening. Overnight, north to northwest winds will average 10-15 kt with seas 1-2 ft nearshore and 2-3 ft offshore. Sunday: High pressure will be located just off the Southeast coast, causing winds to become S to SW 10 kt or less and seas 2 ft or less. Monday: The high will move further offshore while a weak surface trough forms just east of our coastal waters. Additionally, a cold front will slowly approach from the distant west. The interaction between all of these features will lead to increasing winds and building seas, especially late in the afternoon and overnight. Tuesday: The weak surface trough should persist to the east of our coastal waters while the cold front to our west gets closer and strengthens. An intensifying gradient will cause winds and seas to rapidly increase, especially late. Small Craft Advisories are likely for all of the waters. Wednesday: A strong cold front will approach from the west, possibly moving through late. Ahead of the front, winds will be strong, accompanied by hazardous seas. Small Craft Advisories should be ongoing everywhere, including the Charleston Harbor. It's not out of the question some locations could briefly have gale force gusts. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...Freeze Watch from late tonight through Sunday morning for GAZ087-088-099>101-114>116-118-137-138-140. SC...Freeze Watch from late tonight through Sunday morning for SCZ040-042>045-047>052. MARINE...Small Craft Advisory until 10 PM EST this evening for AMZ350- 352-354-374. Small Craft Advisory until 6 PM EST this evening for AMZ330. && $$ NEAR TERM...RJB SHORT TERM... LONG TERM... AVIATION...RJB MARINE...RJB