014 FXUS62 KCHS 220322 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 1022 PM EST Wed Nov 21 2018 .SYNOPSIS... High pressure will prevail through Friday, then a low pressure system will move through on Saturday. A cold front will move through Sunday night followed by high pressure into the middle of next week. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... Temperatures continue to fall quicker than expected within a decoupled boundary layer with nearly ideal radiational conditions in place. Several observations sites across the interior are already in the upper 30s per 21/03z observations and the latest RAP and H3R are both trending cooler with overnight lows. The latest data support lows bottoming out in the mid 30s in the Millen-Allendale corridor. While some recoupling of the boundary layer is likely prior to daybreak as the pressure gradient begins to tighten, it appears there will not be enough wind to preclude scattered frost formation across parts of Jenkins, Screven and Allendale Counties. In fact, some data show a few spots briefly dropping to the freezing mark right at sunrise. A Frost Advisory will be issued from 4-8 AM for Jenkins, Screven and Allendale Counties. Some scattered frost could reach into extreme northern Hampton and northwest Colleton Counties, as well as areas north of Lake Moultrie in Berkeley County, but the impacts areas will remain fairly limited; not enough for an advisory. Elsewhere across the far interior, patchy frost will be possible in mainly sheltered areas. Updated lows range from the mid 30s for areas near the CSRA to the upper 40s along the beaches. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/... Cool high pressure will prevail on Thursday while an upper shortwave digs across the central Gulf Coast states. A coastal trough will slowly develop off our coast Thursday night through Friday, with moist isentropic ascent spreading clouds and scattered showers into the area from the southeast. The best rain chances will be along the coast. A stronger upper trough will move into the mid-Mississippi Valley Friday night, allowing a surface low to develop and move from southern GA to a position off the SC/GA coast by daybreak Saturday. Fairly widespread rain showers are expected across the area Friday night into Saturday morning, quickly abating from southwest to northeast during the day as the low pulls out of the area. Highs will be below normal Thursday and Friday with readings in the mid 50s north to lower 60s south. A warm front will lift north midday Saturday, allowing for a substantial rise in temps with highs reaching the low to mid 70s. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... While a fair bit of uncertainty continues, some improvement in conditions is looking possible Sunday as the low pulls away from the area with a drier atmospheric column filling back in over the region temporarily. An upstream phase-locked low pressure system will then transit northeast near the Great Lakes region, pulling Gulf moisture well inland and supporting an additional period of elevated POPs Sunday night into Monday as a cold front crosses the forecast area. Drier high pressure is then expected to persist into mid-next-week. && .AVIATION /03Z THURSDAY THROUGH MONDAY/... VFR. Extended Aviation Outlook: Flight restrictions become increasingly likely Friday through Saturday as low pressure impacts the area. Otherwise VFR conditions expected. && .MARINE... Tonight: High pressure will build in from the Great Lakes region which will help turn the low level flow from northerly to more northeasterly overnight. As the high builds in, the pressure gradient will tighten considerably, resulting in increasing wind speeds. Winds this evening will start off in the 10-15 knot range, becoming at least 15-20 knots by sunrise Thursday. In fact, winds will strengthen sufficiently across the Charleston County waters and the outer Georgia waters to raise Small Craft Advisories by 10z. The advisories will then expand to other zones beyond that. Seas will increase, becoming 2-4 ft out to 20 nm and 4-5 ft beyond by daybreak Thursday. A tight northeast gradient will exist Thursday through Friday evening due to strengthening high pressure inland and a coastal trough offshore. Solid Small Craft Advisory conditions anticipated during this period outside Charleston Harbor. Thus we've issued Small Craft Advisory headlines for these areas. 25 kt gusts look like a pretty good bet Thursday night into Friday in Charleston Harbor but we held off on a headline for that zone at this time. Seas will gradually subside over the nearshore waters from late Saturday into Sunday but another round of advisories is possible late Sunday into Monday behind another cold front. && .TIDES/COASTAL FLOODING... Strong northeast winds Wednesday night through Friday combined with increasing astronomical effects will likely result in minor to moderate coastal flooding with the morning high tides Thursday through Saturday. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...Frost Advisory from 4 AM to 8 AM EST Thursday for GAZ087-088. SC...Frost Advisory from 4 AM to 8 AM EST Thursday for SCZ040. MARINE...Small Craft Advisory from 7 AM Thursday to 11 PM EST Saturday for AMZ352. Small Craft Advisory from 5 AM Thursday to 5 AM EST Sunday for AMZ350. Small Craft Advisory from 7 AM Thursday to 5 PM EST Saturday for AMZ354. Small Craft Advisory from 5 AM Thursday to 6 PM EST Monday for AMZ374. && $$