Area Forecast Discussion
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267 FXUS61 KPBZ 211524 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 1124 AM EDT THU JUL 21 2016 .SYNOPSIS... Warm temperature and increased humidity can be expected for the weekend. && .NEAR TERM /THROUGH TONIGHT/... Broad high pressure centered over the central CONUS will continue to shunt increasing warmth and humidity over the Upper Ohio Valley Region today. Expect highs about 7 degrees above the averages, with increasing dewpoints fueling rising heat indices over Ohio counties. An approaching shortwave is progged to erode the northeastern flank of the upper high pressure ridge tonight. Changes for the near term period included precip probability adjustments for the potential that ongoing convection over the Great Lakes Region survives mid level warmth, or spawns outflow that ploughes into the diurnally destabilizing airmass over the area. An escalation through "chance" numbers was thus included for the evening hours, and maintained tonight basically north of Interstate 70 as isolated to scattered convection may accompany the actual shortwave. Limitations include the aforementioned CAPE-robbing mid level warmth, fading diurnal support, and lack of inflow support. Morning lows in the moderating airmass were progged close to the previous forecast, i.e. about 5 degrees above the averages. && .SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/... A better chance for rain is expected with another disturbance on Friday. Improved boundary layer moisture and instability with a marginally cooler mid level should be more conducive for showers and storms, although limited deep layer shear should keep the threat of severe isolated. Thereafter, a shortwave ridge extending from the broad Central CONUS high is forecast to continue the warmth and humidity over the immediate area. Dewpoints in the upper 60s, to around 70 F with temperature about 7 to 10 degrees above the averages will generate heat indices in the 95 to 100 degree range for Saturday and Sunday afternoons. A Hazardous Weather Outlook mention was maintained for the Ohio counties as those heat indice projections are flirting with the 100 degrees heat advisory criteria. Convection in the warmth will be limited by warm mid levels and a lack of forcing, so small PoPs will be the rule with hedges dependant of weak disturbances and mesoscale effects. && .LONG TERM /MONDAY THROUGH WEDNESDAY/... A stronger disturbance is forecast to carve the ridge over the Upper Ohio early next week. That system will provide the next, best chance of rain with a shortwave ridge quickly rebuilding in its wake. The flatter flow pattern will moderate temperature in this time frame, although readings are expected to remain above the averages. && .AVIATION /15Z THURSDAY THROUGH MONDAY/... High pressure should maintain VFR conditions and light SW winds through the TAF period. .OUTLOOK /FRIDAY THROUGH MONDAY/... Restrictions are possible in scattered thunderstorms Friday, and again late Sunday and Monday with crossing disturbances. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$ 15/07

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