Area Forecast Discussion
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672 FXUS61 KPBZ 241718 AAB AFDPBZ Area Forecast Discussion...UPDATED National Weather Service Pittsburgh PA 118 PM EDT Wed May 24 2017 .SYNOPSIS...
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An active weather pattern with cool air and periods of widespread rain is expected to last through the weekend as low pressure remains in place across the Ohio Valley. Warmer air and higher humidity are expected to return for the Memorial Day weekend.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Light rain has been noted through the morning in much of the forecast area and has made only a slow northward movement. However, accumulations have been light despite high PoPs in the forecast. Temperature in the low-mid 60s will climb slowly for the remainder of the day as cloud cover thickens in advance of an upper low approaching from the Plains. A shortwave trough in advance of the upper low will lead to widespread rain late this afternoon through tonight as abundant moisture aloft is advected nwd. Given the current presentation on radar upstream, model forecast soundings depicting modest elevated instability overnight may not be far-fetched. Therefore, embedded convective elements may generate moderate rainfall overnight, and the current forecast increases QPF a bit over the previous forecast for tonight. With the widespread rain and cloud cover, temperature will remain rather steady tonight once the wet bulb effect sets in. Uniform minima in the mid-50s will be common in most areas, with slightly-cooler overnight temps in the mountains.
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&& .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
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Widespread morning rain will subside early in the day as a closed upper low deepens in the Ohio Valley and a dry slot asserts itself. As the moist boundary layer in the wake of the morning rain has a brief window to heat, cold air will be advected aloft, leading to steepening mid-level lapse rates and increasing instability despite only a minimal change in surface temperature. Convection-allowing models suggest that showers and storms will be generated quickly in this increasingly-unstable airmass, with a cluster of storms expected to fill in the dry slot by mid- afternoon Thu. Instability is not expected to be sufficient for organized severe weather, but moderate rain rates will be possible in any storms. By Friday, the upper low will have shifted toward New England with northwesterly flow in control and a bit of drier air working into the region. This will be rather short-lived, however, as the H5 ridge axis looks to shift through the area by Saturday with broad southwesterly flow becoming established. This will allow for increasingly-humid and warmer conditions to arrive for the weekend. However, it will also bring an increasing chance for showers and thunderstorms. In fact, some model solutions have featured an MCS traversing the region on Saturday. Stay tuned on that.
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&& .LONG TERM /SATURDAY THROUGH TUESDAY/...
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The pattern going into next week looks to continue to amplify as an upper low again drops into the Mississippi Valley with a downstream ridge popping up rapidly along the eastern seaboard. The Ohio Valley will be stuck between these two areas, with broad southwesterly flow remaining in place and abundant moisture streaming toward the area. As a result, chances for convection will remain in the forecast with temperature near normal.
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&& .AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
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Limited rain showers moving though the area early this afternoon. Mostly VFR conditions with isolated MVFR conditions as low-level moisture increases with a crossing shortwave. VCSH in the TAFs with sct shower coverage this afternoon. Improvement back to VFR all TAFs is expected by late afternoon before deterioration back to MVFR in overnight hours as approaching low pressure arrives. Increasing SE winds are expected today with an increasing pressure gradient, with a few 20-25kt gusts especially for the higher-terrain ports. .Outlook... Areas of non-VFR through Thursday in showers and possible thunderstorms and again for the weekend.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$ Update...Kramar

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