Area Forecast Discussion
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000 FXUS61 KPBZ 291631 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 1231 PM EDT Thu Jun 29 2017 .SYNOPSIS... Temperatures will continue to warm into the weekend, and humidity levels will also increase. This will return the risk for showers and storms, mainly Friday and Saturday. && .NEAR TERM /THROUGH TONIGHT/...
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Current visible satellite imagery shows mostly sunny skies under a shield of thin cirrus. This will further encourage an expedited warm up through the afternoon hours. A shortwave trough will streaming through the southern Great Lakes will move into NY later this afternoon. This will work to flatten out the current shortwave ridge in place. Examination of the morning upper air sounding and the 12z suite of models arriving, have become less enthusiastic about shower and thunderstorm potential this afternoon. Hi-res model guidance continues earlier drying trend this afternoon/evening, largely due to the amount of mid-level warmth acting as a cap. In addition, the shortwave trough is showing signs of erosion on the southern extent, a further indication that the bulk of showers and thunderstorms will stay north of the forecast area. Still, there is some focused ascent that may be able to overcome the mid-level cap, so will keep slight chance PoPs north of Pittsburgh and low chance north of I-80. Lower confidence in the chance PoPs north of Pittsburgh overnight as an additional shortwave trough tries to stream through the upper-level flow. Existence, strength and timing of this wave will largely be dependent on the evolution of afternoon convection across Missouri and Illinois. Gusty south-southwesterly winds will continue through the afternoon due to a strengthening wind profile aloft and rising mixing heights. Dewpoints are rising steadily this afternoon, which will instill a high floor on our overnight lows. Tonight will be several degrees warmer than the last few nights.
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY/...
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Friday will be a similar forecast to today, save for the additional warming and higher dewpoints. This warming in the mid-levels may further strengthen the cap, but the higher dewpoints will encourage instability numbers. Large scale ascent will again be dependent on evolution of upstream shortwave troughs, but we will be closer to the deeper parent trough and associated surface low. For these reasons, think that we still stand a better chance at afternoon convection, especially points north of Pittsburgh. Temperatures Friday will be above normal with much more noticeable humidity levels. Finally, by Saturday the upper-level trough will shift east crossing sweeping the surface cold front through the area. The result is Saturday will remain the best chance for widespread showers and thunderstorms. Exact timing will play a big factor, but current thinking is enough instability and shear will exist to develop a few strong thunderstorms. Thus the current Marginal Risk from the SPC seems prudent. Temperatures will remain near average values, but with dewpoints nearing 70, muggy conditions will hold.
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&& .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
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Dry weather is expected to return Sun/Mon as surface ridging builds underneath the upper trough. Another trough is progged to advance E from the Midwest and Plains regions Tue, though with uncertainty in timing and location limited POPs to the chance category for now on the 4th of July.
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&& .AVIATION /16Z THURSDAY THROUGH MONDAY/... Mainly VFR conditions are expected through the TAF period. Mid/high clouds should continue streaming E from weakening thunderstorms to the W. CU rule/model soundings show SCT to BKN CU by late morning, though bases should still be VFR. A shortwave trough is progged to move across Srn Ontario/NW PA by afternoon with sct showers/tstms expected. Mentioned a VCTS for FKL/DUJ, though capping warmth aloft should limit tstm potential elsewhere. A tightening pressure gradient and mixing should also result in gusty SW winds today. .OUTLOOK... Restriction chances will increase Fri and Sat with the approach and passage of a cold front. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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