Area Forecast Discussion
Issued by NWS Charleston, WV

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000 FXUS61 KRLX 221903 AFDRLX Area Forecast Discussion National Weather Service Charleston WV 303 PM EDT Sat Jul 22 2017 .SYNOPSIS... Strong to severe thunderstorms are possible this weekend with risk for heavy rainfall and potential flooding. Fronts cross late Sunday and again late Monday. High pressure midweek. && .NEAR TERM /THROUGH SUNDAY/... As of 155 PM Saturday... MCS moved across northern zones this morning, producing generally an inch or so of precipitation. Area in the warm sector of a low pressure system moving across Great Lakes region, with sct showers and thunderstorms popping up area wide in the warm, humid, unstable conditions. With the lower FFG/wetter soils across the north, and the potential for additional MCS overnight, went ahead an hoisted a flash flood watch for the area through Sunday morning. This may need to be expanded in area or even in time as we progress, but for now, just decided to issue for the wetter areas/greatest threat region. In addition to flooding issues, the potential for severe exists through much of the night, with strong shear on the order of 40+ kts. SPC has issued a slight risk for most of the CWA through 12Z Sunday, with a slight risk area wide on Sunday for an additional severe thunderstorm threat, as the cold front approaches the area from the north. Frontal boundary should be entering SE Ohio zones towards the end of the period. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/... 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 Limited impacts from upstream thunderstorms early today and no fog formation tonight into Sunday morning. 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. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... 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. && .AVIATION /19Z SATURDAY THROUGH THURSDAY/... 18Z Saturday through 18Z Sunday... As of 200 PM Saturday... Showers and thunderstorms, with heavy downpours, and strong damaging winds are possible during the TAF period. Expect MVFR and IFR conditions in vicinity of storms, along with strong gusty winds. Bulk of convection will generally decrease in coverage from north to south after 12-15Z, but local MVFR and IFR cigs will linger. Additional rounds of showers and thunderstorms towards the end of the period. FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 18Z SUNDAY... FORECAST CONFIDENCE: Medium. ALTERNATE SCENARIOS: Convection could be less widespread than currently forecast. Conditions on Sunday may not improve as quickly as currently forecast. 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. UTC 1HRLY 18 19 20 21 22 23 00 01 02 03 04 05 EDT 1HRLY 14 15 16 17 18 19 20 21 22 23 00 01 CRW CONSISTENCY H H H H H H H H H H H M HTS CONSISTENCY H H H H H H H H H H H M BKW CONSISTENCY H H H H H H H H H H H M EKN CONSISTENCY H H H H H H M L M M H L PKB CONSISTENCY H H M H H H M M M M H M CKB CONSISTENCY H H H H M M L L L M M L AFTER 18Z SUNDAY... IFR possible Sunday in heavy showers and thunderstorms. && .RLX WATCHES/WARNINGS/ADVISORIES...
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WV...Flash Flood Watch through Sunday morning for WVZ007>011- 014>020-027>032-039-040-517>526. Heat Advisory until 8 PM EDT this evening for WVZ005-006-013- 024-025. OH...Flash Flood Watch through Sunday morning for OHZ066-067-075- 076-083>086. Heat Advisory until 8 PM EDT this evening for OHZ087. KY...Heat Advisory until 8 PM EDT this evening for KYZ101>103-105. VA...None.
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&& $$ SYNOPSIS...JMV/SL NEAR TERM...SL SHORT TERM...TRM LONG TERM...TRM AVIATION...SL

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