Area Forecast Discussion
Issued by NWS Charleston, WV

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000 FXUS61 KRLX 190246 AFDRLX Area Forecast Discussion National Weather Service Charleston WV 1046 PM EDT Tue Jul 18 2017 .SYNOPSIS... Developing upper ridge this week, with increasing heat and humidity, and mainly scattered afternoon mountain storms. Storms increase with northwest flow Friday into the weekend. && .NEAR TERM /THROUGH WEDNESDAY NIGHT/...
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As of 1045 PM Tuesday... The last of the showers across far eastern WV and VA are finally diminishing this evening. Expecting close to a repeat performance of last night, with mild and muggy conditions persisting. Fog is likely in river valleys again with clear to mostly clear skies and calm winds. The latest surface observations indicate misty haze starting to develop along the Ohio River and in the Clarksburg vicinity. For Wednesday, an upper ridge will build in with temps once again climbing into the lower 90s and heat indices reaching for the mid to upper 90s under scattered cumulus. Some of the 00Z hi- res guidance is hinting at a small upper impulse approaching the area by tomorrow afternoon/evening and, given the abundant heating, supporting isolated storms. While not out of the question, confidence is low enough as of now to exclude increasing PoPs tomorrow. Regardless, most areas will stay dry and hot with little relief in the humid air tomorrow night.
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&& .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 345 PM Tuesday... Period begins dry with upper and lower level ridging. The upper ridge is an eastward extension of a large upper level high over the central plains and separates an upper level low over the mid Atlantic, and the westerlies across the northern tier of the U.S. Meanwhile, low level southwest flow between the surface high nearby, and low pressure over the midwest, will be feeding into a warm front setting up from that low, eastward and then southeastward into the upper Ohio Valley. It is along this boundary and the ring of fire that thunderstorms complexes will be riding, once initiated upstream where the best low level feed resides. One such complex approaches Thursday but will likely fall apart as it reaches far northern portions of the forecast area, as it gets well downstream of the best feed, and morning and midday cloud top warming occurs. The next complex approaches overnight Thursday night into Friday morning. This one has a chance to make better in roads into northern portions of the forecast area Friday, on account of its earlier timing, and its initiating upstream feed being a little closer. That feed breaks down in favor of another one farther upstream, allowing weak surface high pressure to build in Friday night. Temperatures and dew points reflect the very warm and humid summer air mass in place. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 345 PM Tuesday... Forecast area will reside along the southern edge of the westerlies most of the period. The upper level flow gradually backs from west- northwest to west-southwest Saturday through Monday, as broad upper level ridging crosses, but with embedded smaller scale short waves trough moving through. At the surface, high pressure Saturday morning gives way to southwest flow, as a front and larger upper level short wave trough, slowly approach from the west. The chance for thunder in the area will be tied mainly to daytime heating on Saturday, and then most persistent across northern portions of the area Saturday night. The southeast end of the warm front will be more like a stationary or wavering front, its position crucial in determining where convective complexes track, or vice versa per meso scale outflow boundaries. While model differences exist on the timing of the arrival of the cold front heading into next week, the chance for showers and thunderstorms increases with its approach Sunday, and then decrease with its passage. Models also diverge on whether a wave holds the front up or even pushes it back northward for a time, on or about Monday. Chance PoPs on Day 7, Tuesday, reflect the forecast projection time during this time of year, and increasing model uncertainty at that range, in light of the uncertainty with the front Sunday and Monday leading up to that time. Temperatures and dew points reflect the very warm and humid summer air mass in place, before returning closer to normal, at least on highs, Monday and Tuesday, on account of the effects of the front. && .AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
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18Z Tuesday thru 18Z Wednesday... As of 1045 PM Tuesday... BR already being reported at KPKB with vsby slowly decreasing at KCKB as well. Based on this trend, fog expected to develop a bit faster in these areas than previously forecast. Will update for faster timing in the 19/03Z TAF amendments. As of 745 PM Tuesday... Another tricky night for fog across the area. Given the building upper level ridge, calm sfc winds, and clear skies, inclined to include patchy dense river valley fog again. Expect VFR prevailing through 19/04Z when MVFR fog begins to develop along the OH River. IFR to LIFR fog likely at KPKB by 19/09Z with some MVFR and brief IFR possible at KHTS as well. Did also include a period of MVFR fog at KCRW and IFR at KCKB after 19/10Z based on persistence. Given earlier precip invof KEKN, included MVFR to IFR starting around 19/05Z. KBKW should manage prevailing VFR through the night and into morning with other sites returning to VFR after 19/13Z. Westerly to northwesterly winds are expected Wednesday with 6 to 8 kft SCT CU developing after 19/17Z. FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 00Z THURSDAY... FORECAST CONFIDENCE: Medium for fog tonight. High for VFR conditions Wednesday. ALTERNATE SCENARIOS: Fog timing and extent will likely vary tonight. EXPERIMENTAL TABLE OF FLIGHT CATEGORY OBJECTIVELY SHOWS CONSISTENCY OF WFO FORECAST TO AVAILABLE MODEL INFORMATION: H = HIGH: TAF CONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL. M = MEDIUM: TAF HAS VARYING LEVEL OF CONSISTENCY WITH MODELS. L = LOW: TAF INCONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL. DATE WED 07/19/17 UTC 1HRLY 00 01 02 03 04 05 06 07 08 09 10 11 EDT 1HRLY 20 21 22 23 00 01 02 03 04 05 06 07 CRW CONSISTENCY H H H H H H H H H H M L HTS CONSISTENCY H H H H H H H M M M M L BKW CONSISTENCY H H H H H H H H H H H M EKN CONSISTENCY H H H H H H H M M M M L PKB CONSISTENCY H H H H H H M L L L L M CKB CONSISTENCY H H H H H H H H H M M L AFTER 00Z THURSDAY... Patchy IFR river valley fog is possible Thursday and Friday mornings.
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&& .RLX WATCHES/WARNINGS/ADVISORIES... WV...None. OH...None. KY...None. VA...None. && $$ SYNOPSIS...TRM/SL/DTC NEAR TERM...DTC SHORT TERM...TRM LONG TERM...TRM AVIATION...SL/DTC is the U.S. government's official web portal to all federal, state and local government web resources and services.