Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 220620 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 220 AM EDT Tue Oct 22 2019 .SYNOPSIS... A cold front will approach from the west late tonight and move off the coast late Tuesday. High pressure will rebuild Tuesday night through Thursday before another storm system potentially moves in Friday or Saturday. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... Early this morning: Radar imagery shows that convection is mostly limited to the adjacent coastal waters. This convection is being forced ahead of an advancing warm front and on the leading edge of low level thetaE advection. Instability is mainly limited to the coastal waters, so it doesn`t appear much is going to develop over land areas through sunrise. The main question is what is going to happen to a convective complex ongoing along the Florida panhandle. The good news is that IR satellite shows warming cloud tops so it should be on a weakening trend. The forecast issue is that no model seems to be initializing this feature very well, so it is difficult to determine what it will do as it progresses downstream into southeast Georgia. The forecast tentatively follows the model consensus which is for minimal rain chances through sunrise. && .SHORT TERM /6 AM THIS MORNING THROUGH THURSDAY/... Tuesday: The base of a deep eastern U.S. upper trough is forecast to shift through the Tennessee and Ohio Valley regions. A cold front at the surface is expected to move into our inland zones to near the I-95 corridor during the early afternoon hours. The window for potential destabilization ahead of the front appears to be short and rather limited due to the progressive nature of the front. Surface dew points are expected to fall after mid afternoon as the front shifts to the coast. Prior to fropa, forecast soundings along zones along and east of I-95 show surface based CAPEs 1000-1500 J/KG along with Pwats near 2 inches along with bulk shear of 30 kt and rather unidirectional deep layer flow by early afternoon. There appears to be a brief potential for isolated strong to severe tstms just ahead of the cold front over coastal SC, especially along the Charleston Tri-County in the 17Z-20Z time frame. The overall risk for severe weather otherwise looks rather low given the timing of the front into the I-95 corridor by 18Z. We maintained high chance POPs all areas as convective rains will likely remained scattered. Temps will be warm in the lower to mid 80s with frontal compression and periods of insolation. Wednesday and Thursday: High pressure and dry weather will return to the region. It will be cooler on Wednesday with highs in the mid 70s. We also lowered temps Wednesday night as strong radiational cooling likely to send temps into the mid to upper 40s northwest tier to near 50 at both Charleston and Savannah. Northeast flow on Thursday should keep afternoon temps in the mid 70s most areas once again with a few high clouds around and some increasing coastal stratocumulus south of the Savannah River. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... An upper level trough will develop to the west late in the week. A frontal system is expected to impact the area Friday into Sunday, likely bringing periods of showers though the heaviest rain may remain just inland. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... Challenging forecast ahead at KCHS and KSAV as ceilings impact both locations through the morning. MVFR ceilings are in place at both sites, and upstream observations show IFR ceilings poised to impact KSAV over the next few hours at least on a TEMPO basis. Thinking is that IFR will eventually reach KCHS too, and the forecast contains a TEMPO from 08-12z. MVFR ceilings will remain through the morning until a cold front clears the area from the west. Overall rain chances aren`t that high, so we only carry showers in the TAF`s. VFR will return in the early afternoon at KSAV, and the late afternoon at KCHS. Some low end wind gusts around 20 knots will be possible in southwesterly flow. Extended Aviation Outlook: VFR Tuesday night through Thursday. Increasing chances for low clouds late Thursday night through the weekend along with scattered showers. && .MARINE... Tonight: A warm front will lift north through the waters overnight, allowing winds to veer from the southeast to the south. Speeds are expected to remain well below Small Craft Advisory criteria, topping out in the 10 to 15 kt range. Seas will average 2-3 ft nearshore and 3-4 ft offshore. Tuesday through Friday: A cold front will move offshore late Tuesday with winds veering from southwest to northwest in the wake of the front. We expect a nice punch of cooler and drier air over the waters Tuesday night and this will result in surging and jetting offshore flow. We will likely need a Small Craft Advisory for GA waters 20-60 NM during this time before flow begins to subside on Wednesday. The near shore waters will see decent surging but it appears we may not reach SCA criteria for a substantial length of time. The surface high will build north of the waters mid to late week with moderate onshore flow continuing. Seas may increase to advisory levels next weekend due to persistent northeast fetch and an increasing pressure gradient. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...BSH SHORT TERM... LONG TERM...JRL AVIATION...BSH MARINE... is the U.S. government's official web portal to all federal, state and local government web resources and services.