Area Forecast Discussion
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000 FXUS61 KPBZ 242311 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 611 PM EST Fri Nov 24 2017 .SYNOPSIS... Dry weather is expected today. Shower chances return with the approach and passage of a Saturday cold front. && .NEAR TERM /THROUGH SATURDAY/...
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Clear skies abound across the region this evening even as southerly flow ahead of the next system has encroached. This southerly flow did allow for our afternoon highs to jump back into the 50s earlier today, however the proximity of the front does not seem to be enough to preclude decoupling this evening. The wind field has already relaxed quite a bit, and with dewpoints straddling 20F, some downward pressure will be noted on temperatures through the remaining evening hours. Overnight, high clouds should start to increase ahead of the next system. These clouds really are not reflected in current satellite imagery across the western Great Lakes in accordance with the front, however upper level moisture should start to pool better ahead of the upper wave as it moves farther east into the Great Lakes region. That said, low level moisture greatly lags the upper level fields, and thus all mention of precipitation was removed at least until Saturday. Moving into Saturday, the mid-level wave looks to finally run through the Ohio Valley while the vort field becomes increasingly sheared. A rather paltry mid-level moisture field accompanies it, and even though some right entrance region dynamics should come into play, the lack of moisture through the layer combined with unimpressive ascent mean measurable precipitation may be hard to come back. PoPs were rolled back through Saturday in accordance with this thinking, but the best chances remain across the north and in the terrain. Additionally, thermal profiles support all rain through Saturday at least. Fries
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Upper-level trough swings through Saturday evening, injecting slightly deeper moisture and bringing cooler mid-level air. This should help to re-invigorate shower activity, at least for a few hours. Highest PoPs will be maintained north of I-80 and in the higher elevations. Sometime around midnight, cooling aloft should reach the point where rain can transition to snow. Not expected much more than a coating for most locations north of I-80 and in the Ridges, but a few locations could see up to a half an inch. Low clouds may hang around well into Sunday, especially north of Pittsburgh, but the inversion heights will have dropped to the point where shower activity will no longer be supported. A weak surface trough should result in some cloud increase Sunday night mainly north of Pittsburgh, though precip is not expected. After near to above average temperatures tonight and Saturday, a return to temperatures below seasonal levels is expected Sunday.
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&& .LONG TERM /MONDAY THROUGH FRIDAY/... Generally dry weather is expected through early in the week with a de-amplified flow aloft. A weak trough is progged for a Tue night/Wed passage, with mainly just an increase in clouds. Another trough could result in better precip chances by late week. Temperatures are expected to average near to several degrees above seasonal levels. && .AVIATION /23Z FRIDAY THROUGH WEDNESDAY/... Clear sky this afternoon will give way to high clouds tonight as high pressure moves off to the east. S/SW wind generally from 10 to 15 knots this afternoon will diminish a bit tonight at the surface. However, a low level jet ahead of an approaching front will bring low level wind shear concerns overnight. The jet weakens as the front approaches after sunrise on Saturday, ending the LLWS threat, but clouds will continue to thicken and lower. Scattered showers are possible after 12Z, with ceilings starting to lower towards MVFR levels by the end of the TAF period. .Outlook... Restriction potential will continue through early Sunday, as cold northwest flow changes scattered rain showers to snow showers. && .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.