Area Forecast Discussion
Issued by NWS Charleston, WV

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000 FXUS61 KRLX 131822 AFDRLX AREA FORECAST DISCUSSION National Weather Service Charleston WV 222 PM EDT Thu Aug 13 2020 .SYNOPSIS... A weak frontal boundary will remain stalled over the region through the rest of the work week. Weather remains unsettled through the upcoming weekend. Cold front Sunday night. && .NEAR TERM /THROUGH FRIDAY/... As of 222 PM Thursday... Latest surface analysis shows a quasi-stationary boundary is in place across southern OH and northern WV. This feature has provided enough of a focus for scattered convection across the mountains and more isolated activity across the lowlands so far this afternoon. With MLCAPE values around 1000-1500 J/kg and weak shear, any thunderstorm activity that develops should be pulse type convection. Thus, greatest concern for the remainder of the afternoon and evening is locally torrential downpours that could result in localized water issues given plenty of moisture with PWATs around 1.6 to 1.8 inches and slow storm motions. Since many areas in the mountains received 1 to 2 inches of rain yesterday, FFG values have dropped considerably across eastern portions of our forecast area and with convection mainly focused across the mountains once again today, WPC has a Slight Risk for Excessive Rainfall mainly across our mountainous counties and a Marginal Risk extending to areas near Interstate-79. Thus, will need to keep a close eye on this area through the remainder of the day but thunderstorm activity should remain isolated enough across the lowlands to mitigate a greater flood threat. As instability wanes tonight, the majority of the precipitation activity should diminish but a few light showers may linger into the overnight hours across the mountains. Otherwise, another night of valley fog and/or low stratus appears to be possible as many areas decouple amid moist low levels. After fog lifts Friday morning, attention turns to an upper trough across the middle Ohio Valley that will slowly approach our area through the day. As a result, showers and storms will once again be expected across the area Friday afternoon and evening. Since this feature will provide better upper level support compared to recent days, this should allow for better precipitation coverage across the area. While chances for severe weather should remain low, a warm/moist environment will remain in place so additional downpours localized water issues will be possible once again. && .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/... As of 205 PM Thursday... Southwesterly flow increases Friday night in response to an approaching southern stream wave. This may assist in updraft organization of lingering afternoon convection keeping it going through the evening hours. Stronger forcing arrives by the morning hours Saturday with numerous showers and thunderstorm expected through the day. This will keep temps and surface based instability down a bit compared to previous days, but synoptic forcing, particularly on the left entrance quadrant of the H200 wind max will be more than sufficient to squeeze out very efficient rainfall across portions of the middle Ohio Valley in an environment of near climatological maximum precipitable water values with substantial warm cloud depth. Should still have relatively high flash flood guidance here for the most part with limited rainfall expected Friday - but may begin to see some localized high water issues. Further south, a low level moist convergent axis could cause additional water issues for our southeastern counties where localized heavy rain last night and again tonight precedes it. Currently, WPC has the mountains outlooked as a slight risk for excessive rainfall (where confidence is higher that flash flood guidance will be lower) with a marginal risk over most of the remainder of the area. && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 205 PM Thursday... The 1.6 to 2.0 inch precipitable water plume finally departs to the east Sunday with passage of the trough axis/low level closed circulation making for a mainly dry morning. Will catch a glancing blow from a northern stream disturbance/surface cold front Sunday evening with some additional showers and thunderstorms possible. While mid-level lapse rates nor shear are particularly impressive, could see some better organized updrafts with at least some wind/hail potential with this should the front accelerate and come through in the late afternoon/evening, but for now looks more like a late evening/overnight passage. Cooler and mainly dry weather prevails for Monday and Tuesday under northwesterly flow with surface dew points dipping back down toward the upper 50s feeling pretty good after the recent run of 70s. Sadly, heat and humidity looks to make a return by the end of the week along with a reintroduction of diurnal showers and storms. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... As of 108 PM Thursday... High pressure to the north of the area should maintain mainly VFR conditions across the region through the remainder of the afternoon. However, there may be brief periods of IFR/MVFR restrictions as a stalled frontal boundary over the area should provide enough focus for scattered showers and thunderstorms. Greatest chance for thunderstorm activity is expected to be across the mountains and less of a chance across the lower elevations. Any precipitation across the area should dissipate tonight with the loss of daytime heating. However, light to calm winds and moisture in the low levels of the atmosphere should support the development of fog and/or low stratus overnight. An extended period of IFR or even LIFR conditions will be possible where fog and/or stratus develops. Otherwise, any fog across the area should lift by around 13Z on Friday and VFR conditions should then return to most of the area. However, MVFR stratus may linger throughout most of the morning across the mountains. In addition, an upper level disturbance will approach the area tomorrow with another round of showers and thunderstorms and possible further restrictions by the end of the TAF period. FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 18Z FRIDAY... FORECAST CONFIDENCE: Medium. ALTERNATE SCENARIOS: Timing, duration, and extent of fog overnight may vary from 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 H HTS CONSISTENCY H H H H H H H H H H H H BKW CONSISTENCY H H H H H H H H H H H M EKN CONSISTENCY H H H H H H H H H H H M PKB CONSISTENCY H H H H H H H H H H H H CKB CONSISTENCY H H H H H H H H H H H H AFTER 18Z FRIDAY... Brief IFR in showers and thunderstorms Friday afternoon and evening. Another round of showers and thunderstorms will then be possible on Saturday with additional brief IFR restrictions. && .RLX WATCHES/WARNINGS/ADVISORIES... WV...None. OH...None. KY...None. VA...None. && $$ SYNOPSIS...JP/RG NEAR TERM...RG SHORT TERM...JP LONG TERM...JP AVIATION...RG

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