Area Forecast Discussion
Issued by NWS Charleston, WV

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000 FXUS61 KRLX 220820 AFDRLX Area Forecast Discussion National Weather Service Charleston WV 420 AM EDT Sat Jul 22 2017 .SYNOPSIS...
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Strong to severe thunderstorms possible this weekend. Fronts cross late Sunday and again late Monday. High pressure crosses midweek. Next front late week brings more relief next weekend.
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&& .NEAR TERM /THROUGH TONIGHT/... As of 200 AM Saturday... Cluster of thunderstorms has moved southeast from southern OH to CRW vicinity and updated grids accordingly. HRRR has shown a steady weakening trend but storms have been more persistent. Recent radar and IR satellite trends have indicated a weakening in intensity/warming tops as outflow runs out ahead of the storm cluster. That said, there has been a slight uptick in coverage to the north/east of CRW with some hints of new cells forming to the south of CRW along the outflow boundary. If showers developing along southern flank of outflow can hold together they may approach BKW area by 08z, but pcpn probs are higher to the north across Clay-Nicholas counties. Once this area of precip exits the CWA, high res models keep things mainly dry through the morning. Main concern would then be fog which is already locally dense in some spots. There remains some uncertainty regarding timing of convection later today. Ongoing storms across northern IL/IN are fcst by the CAMs to move east-southeast across OH thru 18z into PA thru 00z Sun. This would put the northern 1/2 to 1/3 of the CWA at greatest risk for severe storms as westerly flow increases aloft. Any outflow from the more organized activity could trigger additional diurnally drive storms further to the south into the WV lowlands. SPC has maintained a SLGT risk across all but the far southern portion of RLX CWA. High PWs along with increasing westerly flow suggests damaging winds as the primary severe threat. && .SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/...
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As of 420 AM Saturday... Convectively active, wavy, roughly west to east oriented front, right over the area first thing Sunday morning, sinks southward through the area during daylight the morning hours. However, with the cold front still west of the Ohio River, models insist the atmosphere easily recovers, with CAPE values climbing to 4 kj/kg over the middle Ohio Valley Sunday afternoon, to go along with modest deep shear into the 30s. Models do show hints of the atmosphere being worked over, with holes in the 2 inch PW air, where values are progged as low as 1.5. With a flat pressure gradient per disorganized low pressure along and south of the cold front, mesoscale processes will be dominant. All things considered, the Sunday forecast is complicated, but likely to be active, especially with forcing being provided by the front, and a digging upper level short wave trough approaching from the northwest. This is reflected in SPCs slight risk for damaging wind, and perhaps even large hail, given thick CAPE through the hail growth level and the modest deep layer bulk shear, although the discussion suggests that the forecast area may be between complexes to the southeast and northwest. The marginal risk for excessive rainfall reflects the variable PW distribution, and the weak low level inflow, but still copious amounts of moisture in place. Flood watch issuance would likely follow a shorter summer fuse similar to convective watches, as the convective complexes evolve and track. With loss of heating, and the ring of fire shifting south as the upper level trough digs in, convection should gradually wane Sunday night. The upper level short wave trough pushes a second cold front through on Monday into Monday night, but moisture will become a bit more limited by then, and storm coverage should be limited and the storms on the move. This should limit any further water concerns, but daytime heating driving CAPE values to perhaps 3 kj/kg in said narrow band could still lead to strong storms in modest deep layer bulk shear. Canadian high pressure brings cooler and less humid air in for Tuesday and Tuesday night. Convection spells high bust potential on highs Sunday or Monday, but lows and dew points will be typical of the summer muggies. Central guidance Monday night through Tuesday night reflect values returning to near normal in the fresher canadian air.
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&& .LONG TERM /WEDNESDAY THROUGH FRIDAY/...
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As of 420 AM Saturday... High pressure exits Wednesday, and afternoon thunderstorms are possible in the mountains on return southerly flow. A cold front approaches Thursday, and moves through Thursday night, with a round or two of showers and thunderstorms likely. Model divergence suggests it may take until sometime Friday to get the front, and its associated precipitation, entirely south of the area. A large canadian high pressure system will bring fresh, cooler and less humid air by next weekend, as the pattern amplifies with a deepening trough in the eastern U.S., and a building ridge in the west. Central guidance reflects warm weather Wednesday through Thursday, followed by near, or even slightly below normal temperatures in the drier air for next weekend.
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&& .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
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As of 200 AM Saturday... Cluster of Tstorms impacting CRW vcnty at 06z should move away from the terminal by 07z. Expect isolated convection to persist moving east-southeast from CRW through 09z. Odds are BKW will be spared but did include VCSH to account for any showers that may form along leading outflow. Abundant low level moisture and partial clearing skies and light/calm surface winds should result in dense river valley fog. For the most part maintained continuity from previous 22/00-03z TAFS with IFR/LIFR conditions at most sites through 12z. For Saturday, more unstable conditions compared with this afternoon are expected with the stationary frontal boundary to our north. Therefore, expect scattered to numerous showers and thunderstorms to produce brief periods of IFR/LIFR due to heavy rain along their patch particularly after 16Z. Strong gusty winds, along with small hail will be possible with any storms. More storms on Sunday. FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 06Z SUNDAY... FORECAST CONFIDENCE: Medium. ALTERNATE SCENARIOS: Additional convection could develop early this morning. Widespread fog may not form overnight into early Saturday morning. 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 SAT 07/22/17 UTC 1HRLY 08 09 10 11 12 13 14 15 16 17 18 19 EDT 1HRLY 04 05 06 07 08 09 10 11 12 13 14 15 CRW CONSISTENCY M M M M M H H H H M M M HTS CONSISTENCY M M M M M H H H H M M M BKW CONSISTENCY M M M M M H H H H M M M EKN CONSISTENCY L M L L L M M M H M L M PKB CONSISTENCY L L L L L M M H L L L M CKB CONSISTENCY L L L L L M M M M M M M AFTER 06Z SUNDAY... IFR possible Saturday night and Sunday in heavy showers and thunderstorms.
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&& .RLX WATCHES/WARNINGS/ADVISORIES... WV...None. OH...None. KY...None. VA...None. && $$ SYNOPSIS...TRM/99 NEAR TERM...99 SHORT TERM...TRM LONG TERM...TRM AVIATION...99

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