Area Forecast Discussion
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000 FXUS61 KPBZ 211351 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 951 AM EDT Fri Jul 21 2017 .SYNOPSIS... Relatively quiet today, a shower or storm is possible south of Interstate 70. Humidity and very warm weather carries through the weekend before a cool down next week. The weekend will be unsettled, especially Saturday with rounds of showers and storms. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Stratocu which is encompassing much of the region will be slow to filter in dry air at mid levels given light winds. This will keep the day more clouds than sunshine. 12Z PIT RAOB illustrates lots of dry air at mid levels which will temper storm development despite very moist low levels. The complex traversing southern Ohio will spawn an outflow boundary which may ignite development across northern West Virginia later today. Any threat of severe weather is low, with the primary impact being cloud to ground lightning. Heat index values will once again be well into the 80s and lower 90s much like the past two days. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/... Model differences arise again this weekend with the timing and strength of a shortwave that will dive through the region in the northwest flow aloft. For now will lean away from the very energetic NAM solution for Saturday/Saturday night. Because of these large differences in the models, have low confidence at this point for most of the weekend. The next major shortwave trough is expected to bring showers and storms to the area sometime on Saturday and continue into Saturday night. In addition to the upper level wave, a surface cold front will drift through the area Saturday night. By favoring a solution closer to the GFS, have slowed likely PoPs on Saturday, focusing them more toward the afternoon hours. There will be many factors at play on Saturday, which will determine the strength of the convection. Amount of sunshine, very warm air aloft, timing of wave, timing of surface front and the possibility of surface reflection developing along the front which will impact the speed at which the boundary moves through. Hopefully, a model consensus will develop over the next few runs. Differences continue into Sunday, as does the low confidence in the forecast. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... A general Great Lakes/northeast U.S. trough will be carved out by Monday, with this pattern holding into mid-week. Temperatures will fall back to near or just below normal during this period. After lingering showers, Tuesday and Wednesday appear dry with high pressure settling over the region. A return to northwest flow may herald increasing rain chances Thursday. && .AVIATION /14Z FRIDAY THROUGH TUESDAY/... After patchy fog clears mid-morning...VFR conditions expected through the day. Slight chance of shra/tsra at southern locations but not enough confidence in coverage for inclusion in the TAF at this time. .OUTLOOK... Additional rounds of storms are expected through the weekend, and morning fog is possible as well. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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