Area Forecast Discussion
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000 FXUS61 KPBZ 212139 AAA AFDPBZ Area Forecast Discussion...UPDATED National Weather Service Pittsburgh PA 539 PM EDT THU JUL 21 2016 .SYNOPSIS... Warm temperature, increased humidity, periodic thunderstorm chances can be expected into early next week. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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540pm update...continue to monitor line of convection slowly moving southeast toward the area. Latest satellite and radar pictures continue to show a slow decay to the activity, which falls in line with 18z operational model runs and the latest hires data. This will be a situation where multiple updates may be needed as the line evolves through the evening. Have lowered pops this evening, attributed to the aforementioned model data, and adjusted overnight lows in line with the latest blended hires guidance. Previous discussion. 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.
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&& .SHORT TERM /6 AM FRIDAY MORNING 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 THURSDAY/... 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 /22Z THURSDAY THROUGH TUESDAY/... High pressure should maintain VFR conditions through the evening. Shower and thunderstorm chances are expected to increase tonight with an approaching shortwave with local restrictions possible. With uncertainty in timing/location of any precip, included only a VCTS for ports north of I 80 where instability should be more favorable, with VCSH mention south. Another weak wave should result in additional scattered thunderstorms Friday afternoon. .OUTLOOK /FRIDAY NIGHT THROUGH TUESDAY/... Restrictions are possible in scattered thunderstorms Friday evening, and again late Sunday and Monday with crossing disturbances. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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