217 FXUS62 KCHS 291548 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 1048 AM EST Tue Jan 29 2019 .SYNOPSIS... A strong cold front will move through the region today, pushing offshore by this evening. High pressure will then dominate into late week. A more unsettled pattern may develop by the weekend and into early next week with moderating temperatures. && .NEAR TERM /THROUGH TONIGHT/... Today: No significant changes made with the latest update. A cold front is expected to move toward the coast bringing some showers this afternoon but really not a lot of rain given the limited available moisture. Best rain chances and amounts will be closer to the CSRA/Midlands/Pee Dee where up to 0.2 inches is possible. Temperatures will be limited by the cloud cover but should be able to reach near 60 inland and lower 60s nearer the Hwy 17 corridor, possibly even mid 60s in some spots. Southwest winds will become gusty this afternoon as high as around 25 mph. Tonight: With the passage of the short wave aloft and surface cold front offshore this evening, whatever is left of the showers will rapidly diminish. An arctic air mass will overspread the region on brisk northwest winds. Skies will become mostly clear or clear, and an advective freeze is expected to near the intra- coastal or US-17 corridor. Black ice does not appear to be a concern given that there will be plenty of time for drying before temps fall below freezing. Lake Winds: A few gusts could approach marginal Advisory criteria of 25 kt on Lake Moultrie later this afternoon through tonight but no plans to issue one at this point due to low confidence. && .SHORT TERM /WEDNESDAY THROUGH FRIDAY/... The large scale upper level pattern will start off with a broad and deep upper low covering much of the eastern U.S.. By Thursday, this upper trough will gradually shift eastward resulting in more zonal flow, followed by slight mid/upper level ridging on Friday. At the surface, strong/cold high pressure will remain centered northwest of the region Wednesday, then shift to generally due north of the area Thursday and Friday. A reinforcing cold front still looks to push through without any precipitation late Wednesday night/early Thursday. Temperatures will start off well below normal Wednesday and into Thursday, then moderate toward normal by Friday. No significant chance for precipitation is expected through the period. In fact, the only period with a slight chance for precipitation is on Friday as a weak wave and associated moisture pass mainly south of the area. The GFS and ECMWF differ on how far north the moisture reaches on Friday, with the ECMWF much further south with the moisture than the GFS. Thus, due to uncertainty, have kept slight chance PoPs for the extreme southeast GA zones for light showers/rain. && .LONG TERM /FRIDAY NIGHT THROUGH MONDAY/... Models continue to indicate a more progressive pattern as the upper flow oscillates between low amplitude mid/upper level ridges and weak troughs/zonal flow through much of the period. The details at the surface are not quite as clear cut. Overall, it appears the surface ridge moves eastward off the mid-Atlantic coast early in the period, with the main storm track and best moisture remaining generally to the north and west of the area. The ECMWF seems a tad more moist than the GFS, especially by Sunday through Tuesday. However, have stuck with a solution of keeping the best chances for PoPs just northwest of the area, leaving slight chance to low end chance PoPs through the period. Model guidance continues to point toward a moderating trend in temperatures. Near to slightly above normal temperatures will be possible Saturday and Sunday, then even warmer Monday and Tuesday as the low level becomes more south-southwest. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... Mainly VFR through 12Z Wednesday. A strong cold front will push east-southeast across the forecast area late this afternoon and evening. Gusty SW winds at 15-20 kt will occur for several hours in advance of the front, and perhaps still a little gusty for a few hours in wake of the front. A band of light showers in association with the cold front should pass over KCHS and KSAV from about 21Z today through 01Z Wednesday. While a very brief period of sub-VFR weather could occur, probabilities are too low to include in the latest set of TAFs. Extended Aviation Outlook: VFR conditions expected to prevail at both KCHS and KSAV through Saturday. && .MARINE... Today: High pressure initially over and near the waters will give way to a strong cold front that approaches by late in the day. Warm advection in advance of the front will temper the mixing, so we have SW winds mainly no more than 15-20 kt through late afternoon. Seas will be a mixture of swells and wind driven waves, building to 3-4 ft within 20 nm and 4-6 ft beyond 20 nm. Tonight: The cold front will quickly pass through in the evening, followed by continental high pressure from both the Gulf Coast region and also the arctic high building out of the Northern Plains. Cold advection and isallobaric pressure climbs of about 2 mb every 3 hours will support NW winds reaching 15-20 kt and gusty on the nearshore waters, and 20-25 kt on the outer Georgia waters. We feel more confident on raising a Small Craft Advisory on the AMZ374 waters where the best mixing will occur, but additional advisories are certain possible elsewhere. Seas will be restricted some by the offshore trajectories, but will still reach 3 or 4 ft within 20 nm and 5 or 6 ft further offshore. Wednesday through Sunday: No highlights are expected through the period with winds mainly 15 to 20 knots or less, and seas 4 to 5 feet or less. High pressure will remain generally well north and west of the waters through Friday, then shift more north and east of the waters Saturday and Sunday. Models indicate the potential for a weak wave of low pressure to move well south of the waters later Friday and into Saturday. Winds/seas may increase a bit during this period, especially over the southern half of the waters, but exact speeds will depend on how strong this system gets and how far north it tracks. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...Small Craft Advisory from 4 PM this afternoon to 7 AM EST Wednesday for AMZ374. && $$ NEAR TERM...RJB SHORT TERM... LONG TERM... AVIATION... MARINE...