Area Forecast Discussion
Issued by NWS Charleston, WV

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641 FXUS61 KRLX 201832 AFDRLX Area Forecast Discussion National Weather Service Charleston WV 232 PM 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 FRIDAY/... As of 230 PM Thursday... Quite a few changes to the near term forecast. First and foremost is an MCS that formed last night, which continues to thrive/move east towards the CWA where daytime heating/unstable conditions have persisted, despite debris clouds across the area from earlier. Went ahead and based on timing of day and continued cooling of cloud tops evident on satellite, and added in a chance of pops across southeast Ohio and northeast KY zones. In addition, there have been small pop up showers this morning/early afternoon across the CWA, and think with the moist unstable conditions, that isold convection cannot be completely ruled out this afternoon, so went ahead and added at least a slight chance everywhere this afternoon. Focus then shifts to later this evening and tonight as a shortwave moves east across the Great Lakes region, driving a frontal boundary south into/towards Ohio zones, and possibly sinking southeastward overnight across the remainder of the CWA, as the flow aloft becomes more northwesterly. Models are all over the place with this, and there is a lot of uncertainty in this, particularly considering the time of day. Went ahead and decided to hang onto a slight chance to chance pops in the overnight hours. There is also a slight possibility that some storms in southeast Ohio could be on the strong side, with 25-40 kts 0-6km bulk shear across the area. SPC has included a slight or marginal risk across most southeast Ohio and adjacent WV zones. On Friday, convection will be on the increase area wide, particularly if there are any leftover outflow boundaries from previous night convection. Moisture will also be on the increase across the area, with dew points climbing a few degrees on Friday. This will push heat indices into the lower 100s across parts of the lowlands, and create the need for a heat advisory. The one concern is whether or not convection and cloud cover will dampen temperatures a bit. But feel public safety is more of a concern at this point, and even if the numbers are not quite advisory criteria, it will still be dangerously hot. In addition, heavy downpours, and strong gusty winds will be possible with any convection on Friday. && .SHORT TERM /FRIDAY NIGHT 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 THURSDAY/... 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 /19Z THURSDAY THROUGH TUESDAY/... 18Z Thursday thru 18Z Friday... As of 130 PM Thursday... Area of convection across western Ohio at 1720Z is slowly progressing eastward, and if it survives, will affect southeast Ohio and northeast Kentucky generally after 20Z. Brief MVFR and IFR conditions and gusty winds up to 30-40 kts is possible. Outside of the initial cluster of storms in Ohio, isolated convection is also possible area wide through 00Z. However, after 00Z Friday, convection will continue to be possible, particularly across parts of southeast Ohio and northern WV, with additional isolated convection possible across southern WV and southwest VA after 09Z Friday. Additional rounds of convection possible after 15Z Friday. FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 18Z FRIDAY... FORECAST CONFIDENCE: Medium ALTERNATE SCENARIOS: Timing and development of convection today and tonight may vary from forecast. Fog development tonight in question, and will depend largely on amount of cloud cover overnight. 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 H H H H H L PKB CONSISTENCY H H H H H H H H H H H M CKB CONSISTENCY H H H H H H H H H H H M AFTER 18Z FRIDAY... IFR possible Friday and Saturday in showers and thunderstorms. && .RLX WATCHES/WARNINGS/ADVISORIES... WV...Heat Advisory from noon to 7 PM EDT Friday for WVZ005>008- 013>015-024>026. OH...Heat Advisory from noon to 7 PM EDT Friday for OHZ083-086-087. KY...Heat Advisory from noon to 7 PM EDT Friday for KYZ101>103-105. VA...None. && $$ SYNOPSIS...JS/SL NEAR TERM...SL SHORT TERM...26 LONG TERM...26 AVIATION...SL is the U.S. government's official web portal to all federal, state and local government web resources and services.