FXUS62 KCHS 161711 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 111 PM EDT Tue Apr 16 2024 .SYNOPSIS... High pressure will persist through the end of the work week. A cold front is forecasted to impact our area this weekend. && .NEAR TERM /THROUGH TONIGHT/... Early this afternoon: No change to the forecast. Previous discussion continues below. Late this morning: All quiet across the forecast area. Ridging aloft and high pressure at the surface will result in a dry forecast with seasonally warm temperatures. Dewpoints are expected to mix out nicely, so it shouldn't feel too bad despite the expected high temperatures. Low-level thickness values are slightly higher than 24 hours ago, so we expect to see highs very similar to yesterday. Look for upper 80s away from the immediate coast, with a few locations hitting 90. Another well developed and progressive sea breeze is expected with water temperatures still in the upper 60s. Tonight: Another quiet night of weather conditions will prevail with sfc high pressure extending from the western Atlantic and the axis of a ridge directly positioned across the Southeast aloft. The pressure gradient will remain weak, resulting in light southerly winds during the night. Although some radiational cooling is expected, a more substantial amount of cirrus clouds across the local area will limit overall cooling. Overnight lows should remain a few degrees warmer than the previous night as a result, generally ranging in the lower 60s inland to mid-upper 60s near the coast. && .SHORT TERM /WEDNESDAY THROUGH FRIDAY/... Wednesday: Mid-level ridging over the East Coast in the morning will weaken as it slowly shifts offshore during the afternoon. Following this will be zonal flow over our area during the evening and overnight. Surface High pressure will be centered west of Bermuda, shifting westward with time. It's western periphery will stretch into our region. Additionally, Low pressure will be moving through the Great Lakes Region. An attached warm front will remain well to the north of our area, while a cold front approaches from the distant west. However, this front is not expected to reach our area, mainly due to the High pushing it away from us, just to the north. The High will keep our area dry during the day. Synoptic models indicate a band of weak showers associated with the cold front approaching our area overnight. However, these showers are expected to weaken/dissipate before they make it into our area. So while we have POPs across our SC counties rising to ~10% overnight, no measurable rainfall is expected. Southerly surface winds during the day will be followed by an afternoon sea breeze quickly moving inland. Despite partly to mostly cloudy skies, the combination of warm 850 mb temperatures and low-level thickness values support well above normal highs in the mid to upper 80s, except cooler at the beaches. Lows will be mild, generally in the 60s. Thursday: The mid-levels will consist of zonal flow over our region in the morning. Ridging will develop over the Southeast U.S. in the afternoon, then strengthen along the entire East Coast into the evening and overnight. This will yield rising heights over our area. At the surface, a weak cold front will be located to our northwest early in the morning. It'll pass to our north during the morning, then offshore in the afternoon, all while weakening. Weak High pressure to our southeast will then stretch into our region during the afternoon and evening. Another front will approach from the distant west overnight. Though, it won't make it to our area during this time period. Any non-zero POPs at daybreak will drop to zero during the morning. The synoptic models generally keep our area dry through the afternoon. POPs start to creep up in the evening and overnight. But they only max out around 10%, so no measurable rainfall is expected. SW surface winds during the day will be followed by another afternoon sea breeze quickly moving inland. Mostly cloudy skies in the morning will become partly cloudy in the afternoon, then persist into the night. Once again, the combination of warm 850 mb temperatures and low-level thickness values support well above normal highs in the upper 80s to around 90 degrees, except cooler at the beaches. Lows will remain very mild, easily in the 60s. Friday: Mid-level ridging over the East Coast in the morning will shift offshore into the afternoon, leading to lowering heights and the development of zonal flow over our area. Surface High pressure located to our Southeast in the morning will move away into the afternoon. Meanwhile, a cold front will approach from the northwest. Moisture creeps higher ahead of the front, with PWATs rising to ~1.5". Synoptic models indicate some showers developing in the afternoon, partly ahead of the front and partly associated with the afternoon sea breeze moving inland. A few rumbles of thunder cannot be ruled out. While clouds should gradually increase into the afternoon, again the combination of warm 850 mb temperatures and low- level thickness values support well above normal highs in the upper 80s to lower 90s, except cooler at the beaches. && .LONG TERM /FRIDAY NIGHT THROUGH MONDAY/... Mid-level zonal flow will prevail overhead into Saturday. Troughing will start to develop over the Great Lakes Region on Sunday, causing heights to lower over our area. This is followed by large scale troughing starting to develop over the eastern half of the U.S. on Monday. A front will approach our area during the weekend, moving through early next week. There remain distinct differences between the models. The GFS has unsettled weather the entire weekend into early next week. The ECMWF has it mostly dry the entire weekend, with Monday being wet. So we continue to go with the blend until the models start to come into better agreement. Temperatures will remain above normal Saturday, then cool down next week. && .AVIATION /17Z TUESDAY THROUGH SATURDAY/... VFR conditions will prevail at KCHS, KJZI, and KSAV through 18z Wednesday. Passage of the sea breeze this afternoon will bring a few low end gusts of 15-18 knots beginning around 19-20z. Extended Aviation Outlook: VFR through Friday. A front could bring occasional flight restrictions in showers on Saturday. && .MARINE... Today and Tonight: High pressure will remain the dominant weather feature locally, extending from the western Atlantic and across the Southeast United States. Expect southwest winds along the western periphery of the high with speeds up to 10-15 kt across most waters, turning south this afternoon as a seabreeze develops and shifts inland. A few gusts around 20 kt are possible along the coast as the seabreeze takes shape, mainly along the Charleston County coast and across the Charleston Harbor. Winds will become light overnight, remaining around 10 kt or less by midnight. Seas will range between 2-3 ft. High pressure will be stationary over or near Bermuda through at least Thursday. It's periphery will, drive our local winds. Each morning expect backing winds, followed by gusty winds along the land/sea interface in the afternoon due to the formation of the sea breeze. Gusts should be around 20 kt in the Charleston Harbor with its passage. Each evening, winds will veer and increase as some coastal jetting develops overnight. Friday is when a front will approach our area. It's uncertain when the front will move through our area, either during the weekend or early next week. But when it does, winds and seas don't appear to be high enough to prompt Small Craft Advisories. Seas should mostly be 2-3 ft. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...BSH/DPB SHORT TERM... LONG TERM... AVIATION...BSH MARINE...DPB