558 FXUS61 KRLX 210922 AFDRLX AREA FORECAST DISCUSSION National Weather Service Charleston WV 522 AM EDT Tue Jul 21 2020 .SYNOPSIS... Hot and humid conditions continue with mainly afternoon and evening showers and thunderstorms through Thursday. A cold front crosses Thursday night. Slightly drier weather for the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 515 AM Tuesday... Updated sky and PoP grids based on latest radar/satellite trends. As of 215 AM Tuesday... A weak mid-level wave/low level convergence at the nose of a very weak local maximum in H850 winds may be able to kick off a few elevated showers this morning, mainly north of the metro valley up toward Clarksburg. Anything that does develop will dissipate quickly after sunrise this morning with dry conditions expected heading into the noon hour. Some mid-level cloud cover looks to tap the brakes on insolation just hard enough to keep heat index values below advisory criteria of 100F this afternoon with daytime highs across the Lowlands mainly 90-93F with afternoon dewpoints 69 to 71. Several diffuse boundaries around along with diurnal upslope in the higher terrain will be the main foci for convection this afternoon in otherwise weak flow. Similar to the last couple days, the main risk with these storms will be downbursts producing locally gusty/damaging winds along with locally heavy downpours containing rainfall rates of 3-4 inches per hour with slow storm motions. SPC has outlooked the entire forecast area in a marginal risk for severe thunderstorms for the aforementioned wind threat. Given pulse type storm mode in the absence of significant deep layer shear will see limited opportunity for training allowing those high rainfall rates to amount to much, but could see some isolated pockets of more significant rainfall accumulations, mainly across northeastern WV and near the mountains. WPC does have these areas outlooked for a marginal to slight risk of excessive rainfall. The most vulnerable areas will be across Braxton, Lewis, Gilmer, Randolph and Harrison county where more moist soil conditions can only support basin rainfall of 1 to 1.5 in an hour prior to small streams rising out of their banks. A weak wave approaching the middle Ohio Valley after sunset may serve to keep convection going a bit into the overnight before precipitation chances fade. A more significant disturbance lurks on the doorstep for Wednesday morning. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 420 AM Tuesday... A cold front crossing this period will bring a slight interruption in the current heat wave. While the cold front crosses Thursday night, This may be a case of the day before the frontal passage being more active than the day of. Models are slower with an upper level short wave trough crossing Wednesday, resulting in timing more coincident with diurnal heating, and a bigger role in pushing a surface cold front toward the area. The short wave will still be close enough for showers and thunderstorms to reach the middle Ohio Valley first thing in the morning. Surface based CAPE will vary according to sunshine, which will depend on the early showers and thunderstorms moving through, but should reach into the 2-3 KJ/Kg range for much of the lowlands, higher where heating is optimized. Mid level flow associated with the short wave trough will introduce 25 to 30 kts of 0-6 km bulk shear, allowing for some storm organization and adding to the threat for damaging wind gusts, compared with the contribution from DCAPE alone. SPC depicts a marginal risk for severe thunderstorms, with the primary threat being damaging wind gusts. Moisture content remains anomalously high Wednesday, with PW values in the 1.7 to 2 inch range, h85 theta e values up around 350K, and surface dew points in the lower 70s across the lowlands. Hence, while storms will be moving a bit faster compared with days prior, a marginal risk for excessive rainfall exists, as depicted by WPC, with areas that get heavy rainfall prior the most vulnerable. Bulk shear decreases as the short wave moves east, away from the area, Wednesday night, and CAPE decreases on loss of heating, so convection should die down. Any wind threat that persists with organized storms should be east of the forecast area by nightfall. However, like a pitch being left over the plate, the cold front is left over the middle Ohio Valley Thursday morning. The front waits for the flat mid and upper level flow Thursday to veer to the northwest Thursday night, in response to amplification of the long wave pattern. As troughing develops off the east coast, and upper level high pressure builds over the midwest, the front finally pushes through the area Thursday night. This leaves the likelihood of showers and thunderstorms for Thursday. However, bulk shear and forcing associated with weaker short wave troughs on the back side of the amplifying long wave trough, spell less of a severe threat. Less moisture across the area, with PW values progged to drop below 1.5 inches, spells less of a flood threat as well. Showers and thunderstorms should diminish from north to south as the front pushes south Thursday night, along with the loss of heating. Central guidance reflects values a little lower for Thursday, with peak indices in the lower to mid 90s across much of the lowlands. Split the difference on a diversion between central guidance highs and hourly temperatures for Wednesday, which results in peak heat indices for the lowlands in the lower to mid 90s north, and mid to upper 90s south. A slightly cooler night is depicted for southeast Ohio behind the cold front Thursday night. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 420 AM Tuesday... Another short wave trough on the back side of an amplifying long wave trough off the east coast, may buckle a cold front across southern portions of the area Friday, to allow showers and thunderstorms there, enhanced by diurnal heating. Bulk shear, moisture levels and instability should remain low enough to keep associated hazard threats to a minimum. This activity should wane quickly from north to south Friday evening. High pressure building from the north at the surface and the west in the upper levels spells a drier weekend, with less chance for diurnal convection. It will still be hot, but not quiet as, along with slightly cooler nights. Models flatten the pattern early next week, with upper level high pressure retreating westward, allowing short waves to reach the area in the resulting upper level northwest flow. With low level moisture back up by then, the threat for showers and thunderstorms returns, with possible strong storms if we get a strong enough short wave trough or ring-of-fire convective complex. Central guidance returns heat indices to the mid 90s across the lowlands for Sunday, and then up to the mid to upper 90s for much of the lowlands for early next week, as lows and dew points return to muggy levels, and lowland highs return to at least the lower 90s. && .AVIATION /09Z TUESDAY THROUGH SATURDAY/... As of 520 AM Tuesday... Any valley fog quickly dissipates this morning. A SCT-BKN 030-040 cumulus field develops by late morning with thunderstorms blossoming this afternoon in the vicinity of a nebulous frontal boundary expected to be draped west to east over north central WV as well as up and down the higher terrain. Highest confidence in convection at EKN/CKB/PKB and BKW where VCTS has been included for now. Winds remain mainly light, except gusty and erratic in the vicinity of thunderstorms. Valley fog likely develops overnight in areas that receive measurable precipitation, highest confidence at EKN and CKB. FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 06Z WEDNESDAY... FORECAST CONFIDENCE: Medium. ALTERNATE SCENARIOS: Will likely need tempos for TS this afternoon at at least CKB and EKN. 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 07/21/20 UTC 1HRLY 09 10 11 12 13 14 15 16 17 18 19 20 EDT 1HRLY 05 06 07 08 09 10 11 12 13 14 15 16 CRW CONSISTENCY M H H H H H H H H H H H HTS CONSISTENCY M H H M H H H H H H H H BKW CONSISTENCY H H M H H H H H H H H H EKN CONSISTENCY H H L L H H H H H H H H PKB CONSISTENCY H H H H H H H H H H H H CKB CONSISTENCY M M M M H H H H H H H H AFTER 12Z WEDNESDAY... IFR possible in showers and thunderstorms Wednesday late morning/afternoon. Valley fog possible Thursday morning. && .RLX WATCHES/WARNINGS/ADVISORIES... WV...None. OH...None. KY...None. VA...None. && $$ SYNOPSIS...TRM/JP NEAR TERM...JP SHORT TERM...TRM LONG TERM...TRM AVIATION...JP