Area Forecast Discussion
Issued by NWS Charleston, WV

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000 FXUS61 KRLX 201400 AFDRLX Area Forecast Discussion National Weather Service Charleston WV 1000 AM EDT Thu Jul 20 2017 .SYNOPSIS... Convective activity on the increase into the weekend with heat persisting. Frontal system passes early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 950 AM Thursday... Made a few tweaks to the forecast this morning. One was to tweak both hourly temperatures and max temperatures today slightly. Several locations are already several degrees higher than previously forecast or what models are depicting, and raised some max temperatures today a degree or two to account for this. Still lots of uncertainty in what exactly is going to happen with convection as the day progresses. A shortwave will move east across the Great Lakes later today and tonight, pushing a frontal boundary south into Ohio zones. Based on timing, much of the convection may dissipate/weaken before entering the CWA, with models depicting dry air in mid levels. However, as we progress into the night, higher moisture air should overspread the region, with a northwesterly flow taking hold aloft, with convection possibly making it into the northern zones late tonight. As with previous forecaster, will wait for more model runs to decide whether to increase pops across the north late tonight, and leave at chance. As of 620 AM Thursday... Inserted low pops this afternoon over southeast Ohio for pop up convection, as the models shift the aforementioned dry slot eastward faster. Organized convection is still uncertain for tonight and will maintain high chance pops in the north. As of 315 AM Thursday... Models have upper ridging over the Ohio Valley continuing to weaken with upper flow west northwesterly. A short wave will cross the Great Lakes into New England later today and tonight, and this will allow a frontal boundary to drop southward. Most of the model guidance keeps the front just north of our area by 12Z Friday. A mid level dry slot crossing the area today, and the front still well to the north, will keep convection at bay today, despite the high low level moisture. So, will keep the area precip free today. It will be hot and humid with highs mainly in the lower 90s, but heat indices are still expected to remain below advisory criteria. Deeper moisture with pw`s aoa 2 inches pools along the front today as it drops south through the Great Lakes, which will likely generate convection with the front. The big forecast problem will be for tonight, concerning convective that develops along the front to the north this afternoon. Corfidi vectors with west northwest flow aloft will tend to push any frontal convection south and east ahead of the front. Although model pops are not aggressive at all, they do show the deeper moisture driving southward thru the northern half of the area by 12Z Friday. So, will bring convection southward into central WV by Friday morning, but given the diurnal factor and low model pops, will keep convection on the scattered side for now. Will leave for the day shift to monitor for a possible MCS tonight. Finally, it will be warm and muggy tonight. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 305 AM Thursday... The short term transition brings an increase in the mid level dewpoints and a marked increase in the surface based instability Friday and especially into Saturday. As advertised, northwest flow aloft will drop into the CWA, as well as a weaker surface boundary from a surface low lingering in the plains states. The low level frontogenetic forcing with the boundary will be less than impressive, but even weak forcing with the temperatures nearing their convective temperatures and disturbances aloft in the 500mb gradient should be able to initiate convection. In the meantime, lowland dewpoints and temperatures will couple to push and exceed the 100 heat index criteria Friday and Saturday. Will mention again in the HWO. Some concern about cloud cover and showers possibly keeping those values at bay a bit, but need to push that threat. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 305 AM Thursday... As the upper ridge retreats to the west, plains area surface low will finally track eastward as an upper level open wave drops into the Great Lakes. Expect some organization to the convection as the frontal system approaches and the magnitude of the low level frontogenesis increases. This should lead to some early next week relief to the temperatures and dewpoints for a short period of time. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... 12Z Thursday thru 12Z Friday... As of 620 AM Thursday... Upper ridging continues to weaken. A frontal system over the upper midwest early this morning will drop southeastward today and tonight, but staying just north of our area by 12Z Friday. Today... The more widespread MVFR/patchy IFR haze/fog for the river valley areas will dissipate by 13Z. Thereafter, generally SCT 5000-7000 feet AGL except becoming BKN far northwestern portions of area by 00Z. Models have a mid level dry slot crossing today ahead of the front, bu deeper moisture moves back into southeast Ohio later this afternoon. Associated convection and deepest moisture associated with the front is expected to remain mostly north of our area until around 00Z. Thus, except for popup convection southeast Ohio later this afternoon, will leave convection out of the area and the major TAF sites today. Tonight... Even though frontal system sags ever so slowly southward and will remain just north of our area by 12Z Friday, west to northwest flow aloft is expected to carry the frontal deeper moisture and convection southward across the north and into central sections of WV by 12Z Friday. However, despite deep moisture, the diurnal timing will tend to diminish the convection, and will keep the convection as scattered. So, given this uncertainty with the convection, will go with VCSH after 04Z for the northern TAFS of PKB, CKB and EKN for now. Dry south. Generally VFR ceilings 4000-7000 feet across the north, except lower in scattered convection, while SCT mid level clouds prevail in the south. Near calm winds by night, and west winds 5 to 10 KTS by day. FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 12Z FRIDAY... FORECAST CONFIDENCE: Medium ALTERNATE SCENARIOS: IFR Fog development early this morning may vary from forecast. Timing and southward extent of convection may also vary. 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 12 13 14 15 16 17 18 19 20 21 22 23 EDT 1HRLY 08 09 10 11 12 13 14 15 16 17 18 19 CRW CONSISTENCY M H H H H H H H H H H M HTS CONSISTENCY L M 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 H H H H H H H H H H M PKB CONSISTENCY M H H H H H H H H H H M CKB CONSISTENCY M H H H H H H H H H H M AFTER 12Z FRIDAY... Patchy IFR river valley fog is possible Friday morning, and Friday and Saturday in showers and thunderstorms. && .RLX WATCHES/WARNINGS/ADVISORIES... WV...None. OH...None. KY...None. VA...None. && $$ SYNOPSIS...JMV/26 NEAR TERM...JMV/SL SHORT TERM...26 LONG TERM...26 AVIATION...JMV

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