Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 190939 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 439 AM EST Mon Feb 19 2018 .SYNOPSIS...
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A warm front is expected to lift across the region today. A large area of high pressure will then prevail for much of the week. A cold front should approach the area early next week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Pre-Dawn: The pattern features a coastal trough and inland wedge. There was a large subsidence inversion aloft and multiple low-level inversions resulting in widespread low clouds. Stratus will continue to expand and likely result in patchy to areas of fog nearing daybreak as it builds down. Latest guidance suggests we may not see a lot of dense fog, but we will be watching southern GA zones where conditions appear most favorable. Temps will linger in the mid and upper 50s. Isolated/spotty showers are possible along coastal parts of the Charleston Tri-County area. Today: Upper ridging across the southeast Atlantic is forecast to build northwest over the southeastern United States. The surface coastal trough will weaken as boundary layer flow becomes more uniform and veers southerly. low level thickness values will be much warmer today and once we see the morning low clouds and fog disperse, we will see more sunshine this afternoon and temps will respond with highs reaching the upper 70s to around 80 degrees inland from the beaches and barrier islands. Dry weather should prevail with only slight chances for a light morning shower or sprinkle across parts of Charleston and Berkeley counties as the coastal trough lifts north. Tonight: Models suggest that conditions will be favorable for a more substantial stratus build-down scenario given higher low level dew points and sustained Atlantic moisture flux below the subsidence inversion. Low clouds should expand inland during the evening hours and fog may be dense in some areas across the region overnight. Low temps will be very mild once again with readings in the upper 50s to lower 60s from inland to coast.
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&& .SHORT TERM /TUESDAY THROUGH THURSDAY/...
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A large ridge of high pressure centered over the western Atlantic will extend across the Southeast United States, setting up unseasonably warm temps through mid week. 1000-850mb thickness values support high temps some 15-20 degrees above normal, peaking in the upper 70s to lower 80s each afternoon. These temps could potentially break record-setting highs Tuesday and Wednesday noted in the climate section below. The expansive ridge will also be responsible for producing a strong inversion over the area each day, helping maintain precip-free conditions for much of the week. Other than warm temps, the main issue should come during late night/early morning hours when a light southeast wind drives moisture onshore and leads to stratus that potentially builds down near the sfc. Given the setup, bouts of fog will be possible as overnight lows dip into the lower 60s. Patchy fog remains in the forecast Tuesday night and Wednesday night.
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&& .LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
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A large ridge of high pressure centered over the western Atlantic will be the primary contributor to the weather over the Southeast United States, allowing warm conditions to persist through the weekend. In general, temps will be well above normal, peaking into the upper 70s/lower 80s Friday, Saturday and Sunday. Overnight lows will be mild, ranging in the upper 50s to lower 60s. The next chance for more substantial shower chances should arrive late Sunday or Monday as a mid/upper trough passes to the north with a southward extending cold front that shifts through the Southeast. Once fropa occurs, temps should be slightly cooler, peaking in the mid/upper 70s on Monday.
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&& .AVIATION /09Z MONDAY THROUGH FRIDAY/...
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At 09Z, stratus had developed many areas and these low clouds will expand and lower overnight resulting in IFR or even late night LIFR conditions locally. Low clouds will take a while Monday morning to lift and eventually scatter by afternoon. Models show an impressive flux of low cigs advecting onshore Monday evening resulting in another round of flight restrictions. Extended Aviation Outlook: Flight restrictions are possible Tuesday night and Wednesday night, mainly due to low stratus and/or fog. Otherwise, VFR conditions should prevail under high pressure.
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&& .MARINE...
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Stratus was noted over the waters on satellite and we suspect there will be reports of visibility restrictions over the waters this morning, perhaps lingering over GA waters this afternoon. Tonight, there will likely be foggy conditions developing on/near the land/sea interface impacting the harbors and sounds as well as the Savannah River Entrance. Marine dense fog advisories are possible. A coastal trough will weaken through tonight with very stable and cool shelf waters reluctant to respond to the developing south to southeast return synoptic flow. Over the coolest near shore waters, the flow will likely remain from the east will speeds less than 15 kt. Over our outer GA waters, there should be a bit more of a southeast component by tonight. Seas will average 2 ft or so near shore and 3-4 ft well offshore closer to the Gulf Stream. Tuesday through Saturday: High pressure will dominate over the coastal waters through late week. The pattern suggests fairly quiet conditions in regards to winds/seas. However, lower 60 dewpts will spread across the coastal waters as a light southeasterly wind develops by midweek. The setup could potentially lead to some sea fog over slightly cooler nearshore waters Tuesday through Thursday. In general, southeast winds should remain at or below 10-15 kt under the influence of strong high pressure. Seas will range between 2-4 ft in nearshore waters and peak near 4-5 ft in offshore Georgia waters.
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&& .CLIMATE... Record Highs Tuesday 2/20 CHS 82 1991 SAV 84 1991 CXM 78 1918 Wednesday 2/21 CHS 82 1991 SAV 83 1991 CXM 80 2001 && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM... SHORT TERM...DPB LONG TERM...DPB AVIATION...DPB MARINE...DPB CLIMATE...

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