Area Forecast Discussion
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000 FXUS61 KPBZ 212127 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 527 PM EDT Mon Aug 21 2017 .SYNOPSIS... A sequence of weak upper-level disturbances will provide isolated showers and thunderstorms today. Widespread showers and thunderstorms are expected on Tuesday as a cold front crosses the region. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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A weak dewpoint discontinuity currently traverses Indiana and Ohio into NW PA generally along I-80. To the west, a weak short wave trough is working down this boundary, helping to initiate convection along it. This should last a few more hours as we are generally right near peak heating at this time. This is especially the case as we need to overcome the roughly 5 degrees lost during the eclipse. That said, a rather pervasive cirrus shield has advanced eastward over much of the CWA to the south of this dewpoint gradient, and that along with the weakened heating from the eclipse has really been the death knell for cumulus redevelopment. With dewpoints in the 70s and heating having resumed, a few pop ups cannot be ruled out, however anything organized seems highly specious as we get deeper into the evening. Convection should wave by later in the evening, however convective blow off will likely yield a less than clear sky through the balance of the night. Fries
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/... A strong upper low will dig into the Great Lakes on Tue and acquire a neutral to negative tilt through the day in concert with the movement of a mid-level jet maximum. The system`s associated cold front will approach the Ohio Valley during the early evening, but a prefrontal trough is expected to be the focus for daytime convection in the area. Abundant low-level moisture, steepening lapse rates and strong effective bulk shear will support the development of strong to severe thunderstorms by early afternoon along the sharpening sfc trough. CAPE on the order of 2000 J/kg and effective shear of 40-50kt will promote organized, severe convection. Given the deep-layer shear orientation roughly parallel to the sfc feature, storms should congeal quickly into an intense convective line that will move sewd into the instability axis. Damaging wind gusts will be the primary threat, but hail also is possible in more intense, cellular updrafts ahead of the line. Storms will exit sewd by early evening with rain lingering into the evening behind the storms as the cold front traverses the region. High pressure will build in on Wed/Wed eve, with little chance of rain as dry air invades. && .LONG TERM /THURSDAY THROUGH MONDAY/... Although ensembles still show spread in their upper pattern solutions, it appears that broad surface high pressure under an ern-CONUS trough/midwestern ridge pattern is progged to support a generally-dry air mass through the period. Daily temperatures below climatological average can be expected through early next week. && .AVIATION /21Z MONDAY THROUGH SATURDAY/... General VFR is expected for the period although a crossing shortwave may spawn isold to sct convection. Expect rapid deterioration of conditions on Tuesday as widespread precip will herald the advance of cold front. .Outlook... With passage of an early Wed cold front, general VFR can be expected for the remainder of the week. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.