364 FXUS62 KCHS 161121 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 721 AM EDT Sun Oct 16 2022 .SYNOPSIS... High pressure over the area will move offshore tonight. A strong cold front will move through the region Monday night, followed by cool high pressure into next weekend. && .NEAR TERM /THROUGH TONIGHT/... The forecast area will remain between sfc high pressure centered over the western Atlantic and a cold front over the Ohio River Valley. This pattern will provide the region with light return flow. Morning IR satellite indicated cirrus increasing from the west. Based on satellite trends and near term guidance, cirrus should remain FEW through most of the day, increasing to SCT by late this afternoon to early evening. The combination of light return flow and mostly sunny conditions, high temperatures are forecast to range in the mid 80s for most areas this afternoon. Tonight, the cold front is forecast to push across the Southern Appalachians, emerging over the Foothills by daybreak Monday. The pressure gradient between the cold front and western Atlantic high should remain high enough to support light and steady SW winds through tonight. HREF indicates that BKN-OVC high and mid clouds will build across the region tonight. The combination of steady SW winds and increasing sky cover should limit cooling to the low to mid 60s. && .SHORT TERM /MONDAY THROUGH WEDNESDAY/... A powerful closed upper low over the Great Lakes region will shift southeast on Monday. At the surface, cold Canadian high pressure will drop southeast across the Central United States, pushing a strong cold front through the area Monday night. Some moisture advection will occur ahead of the front, with surface dewpoints rising into the low/mid 60s near the coast Monday afternoon. With high temps in the lower 80s, surface-based CAPE of 500-1000 J/kg could develop, mainly across the eastern fringe. At least isolated showers and thunderstorms should develop late Monday afternoon or early evening as the front sweeps through, though the best coverage is expected over the marine area once the front moves offshore. Given the modest destabilization and 40-45 kt bulk shear values, SPC continues to highlight the eastern half of our area in a Marginal Risk for severe thunderstorms. Any precipitation that occurs with the front should be off the coast by mid to late Monday evening. Much colder, drier air will overspread the region late Monday night through Wednesday. Strong cold air advection will result in a chilly Tuesday night, with lows dipping into the low/mid 30s far inland, with lower 40s coastal. Some frost is possible far inland but a few knots of wind could preclude more widespread frost development. && .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/... Wednesday night will be the coldest so far this season due to ideal radiational cooling. Clear skies, light winds, and a cold airmass will yield lows in the low to mid 30s across the western half of the area, likely resulting in at least patchy frost. Dry weather and gradually moderating temperatures anticipated Thursday through Saturday. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... VFR conditions are expected at KCHS/KJZI/KSAV terminals through 12Z Monday. Extended Aviation Outlook: Isolated showers and thunderstorms possible late Monday afternoon and early evening ahead of a cold front. && .MARINE... The forecast area will remain between sfc high pressure centered over the western Atlantic and a cold front over the Southern Appalachian region today and tonight. Winds across coastal waters will remain from the south around 10 kts today. Winds are expected to shift from the southwest and increase to 10-15 kts tonight. Seas are expected to generally range between 2-3 ft through the near term. On Monday, southwest winds will increase out ahead of the cold front. Gusts over the SC nearshore waters as well as Charleston Harbor could approach 25 kt during the afternoon hours. Winds will turn to the northwest late Monday night behind the front, then more northerly by Tuesday evening. The strongest wind surge is expected Tuesday night where some 25 kt gusts will be possible. Small Craft Advisories may eventually be needed. Northerly winds will continue through late week but speeds will diminish as the surface high expands over the waters. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...NED SHORT TERM...JRL LONG TERM...JRL AVIATION...JRL/NED MARINE...JRL/NED