Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 180831 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 431 AM EDT Thu Oct 18 2018 .SYNOPSIS... Cooler high pressure will build over the region today and Friday before shifting offshore Saturday. A stronger cold front will advance through the area Saturday night, followed by cool high pressure through the middle of next week. && .NEAR TERM /THROUGH TONIGHT/... Pre-dawn: The cold front was pushing toward the GA/FL border early this morning with gradually increasing northeast flow and falling surface dew points lagging just a bit behind this morning but on schedule to push south through the area prior to daybreak. Cloud coverage is somewhat tricky as elongated areas of mid and high clouds extend over the southeast states but not much in the way of stratocu to this point. Today: High pressure is forecast to build east from the Ohio Valley to the Mid Atlantic region and expand south over GA and the Carolinas. Forecast soundings across our region indicate moisture at stratocu level is expected to pool across southern GA under a well defined inversion between 3-5 kft. Across our SC zones, it looks a bit drier in that layer but soundings suggest more in the way of mid level moisture and higher expectations of altocu hanging around. Given the complexity of the potential sky coverage today, partly sunny skies were an average call at this point. It should remain dry with only small chances for isolated showers along the immediate coastal areas closer to the Altamaha River where slightly deeper moisture is expected to linger into the day. The break from the very warm temps has arrived with temps in the 70s today, coolest northern zones where highs may struggle to top the lower 70s. Across southeast GA, temps should reach the mid 70s with some upper 70s far southern zones (especially if we lesser coverage of stratocu). Breezy conditions on the beaches and barrier islands where northeast flow remains steady in the 20-25 mph range between tight thermal and moisture gradients from north to south and between land and the Gulf Stream. Tonight: We should see a decent low level gradient across much of the forecast area between high pressure over NC and a weak coastal trough off of northeast FL. Dry weather and cooler temps are on tap for the most part. Lows will have dramatic gradients over the area, ranging from the upper 40s northwest tier to the upper 60s on southern barrier locations such as Sapelo Island GA. && .SHORT TERM /FRIDAY THROUGH SUNDAY/... Dry high pressure is expected to prevail over most areas Friday into early Saturday morning. A more developed coastal trough was noted in the synoptic 18/00Z model suite by late Friday night. Model prognoses vary, with the NAM and Canadian most aggressively resolving the trough, and the GFS and ECMWF a little slower with development and overall weaker. Nonetheless, this feature could be responsible for isolated shower development primarily over southernmost coastal waters, though some brushes with nearby coastal zones cannot be entirely ruled out. By Saturday, the next cold front is likely located near the Appalachian mountains and rapidly progressing towards the forecast area. Compression in advance of the front will drive maximum temperatures higher. Of note, the latest GFS fails to show overly impressive soundings for precipitation potential, and peak POPs Saturday have been lowered slightly. The front will then clear the forecast area by late Saturday night, and further declining POPs and temperatures ensue. Behind the front, a rain-free Sunday will feature below-normal temperatures. && .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... Mostly dry conditions and moderating temperatures are expected heading into early next week as surface high pressure builds in behind the cold front. The GFS and ECMWF indicate development of a coastal trough as high pressure pushes offshore Monday night into Tuesday, and slight chance POPs remain for southeasternmost zones. Forecast uncertainty increases after Tuesday with possible pressure falls near the south-central plains. && .AVIATION /07Z THURSDAY THROUGH MONDAY/... VFR. Northeast winds will increase toward daybreak with breezy conditions into midday. Extended Aviation Outlook: VFR conditions are expected to prevail at both terminals. Brief flight restrictions will be possible due to reduced ceilings and/or vsbys under showers as a cold front approaches and crosses the region Saturday into Saturday night. && .MARINE... A significant northeast surge was building down our coast pre-dawn and this trend will continue through the daytime hours, reaching southern GA waters before mid morning. Small craft Advisories are in effect all waters except the CHS Harbor where near-SCA are certainly possible later this morning. Winds will increase to 20-25 kt across most waters and tend to weaken this evening over northern SC waters while model trends keep a strong low level gradient and steady NE flow to the south of the Savannah River well into tonight. Seas will build to 4-6 ft near shore and 5-7 ft well offshore and slowly decrease below SCA levels over CHS waters later tonight. Ongoing Small Craft Advisories will gradually drop off as elevated winds and seas continue to subside through later Friday. Winds will turn onshore later Friday as surface high pressure shifts further offshore, and continue veering SW into Saturday as the next cold front rapidly advances towards the region. With cold front passage expected late Saturday night into pre-sunrise Sunday morning, winds will veer generally north. Rapidly building high pressure will lead to another surge in winds/seas, and Small Craft Advisories may be needed by early Sunday morning. Winds then veer more northeasterly as conditions gradually subside through the day Sunday into Sunday night, with NE flow generally persisting through early next week. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...Small Craft Advisory until 11 PM EDT this evening for AMZ350- 352. Small Craft Advisory until midnight EDT Friday night for AMZ374. Small Craft Advisory until 6 AM EDT Friday for AMZ354. && $$ NEAR TERM... SHORT TERM...JMC LONG TERM...JMC AVIATION...JMC MARINE...JMC

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