Area Forecast Discussion
Issued by NWS Charleston, WV

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000 FXUS61 KRLX 220747 AFDRLX Area Forecast Discussion National Weather Service Charleston WV 347 AM EDT Tue Aug 22 2017 .SYNOPSIS... High pressure continues into Tuesday. Strong cold front late Tuesday into Tuesday night. Cooler and drier high pressure into the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 315 AM Tuesday... Models are in agreement on a strong cold front dropping southeast through the area tonight under an amplifying northern stream upper trough. This system has both dynamics and a very moist and unstable airmass in place ahead of the front. This will likely result in a well defined line of strong to severe thunderstorms, supported by SPC forecasts. The big forecast question then is the timing of this line to move across. There are model differences in that some are initially prefrontal along a surface boundary laid out by overnight convection back in Indiana, while others are closer to the front itself. Will go with the prefrontal boundary scenario, in which the line should regenerate by early this afternoon from northeast Ohio to north central Kentucky. The line is expected to intensify and accelerate southeast across the area this afternoon into early tonight, possibly accompanied by damaging winds and large hail. The most likely areas for potential severe thunderstorms will be over northeast Kentucky, southeast Ohio and the northwest half of West Virginia this afternoon and evening, then weakening as the line gets into the southeastern half of West Virginia and southwest Virginia late this evening and early tonight. Ahead of this line, there may be isolated pop up storms this afternoon. This scenario will take away much of the convection with the cold front itself that follows tonight, so will keep much lower pops behind this line and until the front passes. It will be hot and more humid today under sunshine ahead of the line, with highs 85 to 91. For tonight, intensity of the line of convection as it moves across the south and east will diminish with loss of heating, while showers will be ending from west to east in the low lands following the front, as drier air filters in. Any lingering showers by dawn will mostly be confined to the central and southeast mountains with some cold advection northwest upslope flow acts on some remaining low level moisture behind the front. && .SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/... As of 220 AM Tuesday... The post frontal environment will dry out quickly in northwest flow with broad scale surface high pressure building into the Ohio Valley. Some low level moisture advects back into the area in wrap around moisture, which would suggest sprinkles to isolated shower chances over the far northern CWA. However, leaving this out for now, and should be firmly entrenched north in the PBZ area. Temperatures give a slight hint to the twilight of summer with lowland 70s and dewpoints in the 50s for the short term. && .LONG TERM /SATURDAY THROUGH MONDAY/... As of 220 AM Tuesday... Outside of some isolated mountain showers, the extended is dry on the front end, with high pressure centered over eastern Canada controlling our forecast area. An upper level low will dig into the upper Mississippi Valley, meander eastward as it becomes cut off, and slow advects chances for showers into the western zones. As mentioned in past discussions, the dominant ridge/trough pattern across the CONUS from west to east will remain dominant. Expecting a slight increase in temperatures from the short term. && .AVIATION /07Z TUESDAY THROUGH SATURDAY/... 06Z Tuesday thru 06Z Wednesday... As of 215 AM Tuesday... Strong cold front moves across the area late this afternoon and tonight, well preceded by a line of strong to severe thunderstorms. Thru 13Z... Cirrus on the increase early morning. This, and some flow should keep dense fog in only the most protected valleys. Did include LIFR at EKN in the deeper valley and with the thinest clouds til 13Z. Elsewhere, marginal MVFR valley fog at best possible. Today after 13Z... Out ahead of aforementioned line of thunderstorms, VFR with generally cirrus this morning, then SCT-BKN clouds 4000-6000 feet AGL after 17Z with isolated thunderstorms mainly west. Light south winds becoming southwest 10 to 20 KTS and gusty by late morning. Best estimate. Line of TSTMS expected to arrive at Ohio River 20Z-22Z and CKB-CRW line 23Z-01Z and into the mountains 01Z- 03Z. Conditions varying greatly within this line, lowering to IFR at times, so will put PROB30 in TAFS at this distant time frame, with strong gusty west winds and hail possible. Behind this line, outside of mountains generally VFR ceilings 3500-5000 feet with scattered showers for 1-3 hours, then clouds decreasing in the west. In the mountains, MVFR ceilings and showers will linger thru rest of period. Winds becoming west 5 to 8 KTS behind the front which will reach the mountains around 06Z. FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 06Z WEDNESDAY... FORECAST CONFIDENCE: Medium. ALTERNATE SCENARIOS: Main line of storms with cold front later today could arrive a bit earlier than 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. DATE TUE 08/22/17 UTC 1HRLY 06 07 08 09 10 11 12 13 14 15 16 17 EDT 1HRLY 02 03 04 05 06 07 08 09 10 11 12 13 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 M L L L L L L M H H H M PKB CONSISTENCY H H H H M M M H H H H M CKB CONSISTENCY H H H H H H H H H H H M AFTER 06Z WEDNESDAY... IFR possible in low stratus and showers/fog into early Wednesday for mountains. River valley fog possible each morning through the weekend. && .RLX WATCHES/WARNINGS/ADVISORIES... WV...None. OH...None. KY...None. VA...None. && $$ SYNOPSIS...JMV/26 NEAR TERM...JMV SHORT TERM...26 LONG TERM...26 AVIATION...JMV

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