Area Forecast Discussion
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546 FXUS61 KPBZ 262141 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 541 PM EDT Mon Jun 26 2017 .SYNOPSIS... Upper low pressure will maintain cooler temperature and a periodic shower chance for the first half of the week. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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Showers and thunderstorms initially triggered by Lake Erie lake breeze are continuing to blossom this evening, as the first of two upper-level shortwave troughs swing through. Steep lapse rates, bolstered by continued cooling in the mid-levels, will keep the threat of scattered thunderstorms going through the evening, primarily north of Pittsburgh. Even still, only modest SBCAPE exists to go along with marginal vertical shear values. While a stronger thunderstorm with small hail cannot be ruled out, widespread deep convection is not expected. A second, more vigorous shortwave trough will approach tonight bringing another round of scattered showers. This wave, clearly evident on water vapor over Lake Michigan, is responsible for numerous thunderstorms stretching from western IL through western OH. These will continue to push east late this evening, and reach our westernmost zones just after 00z. Latest hi-res models, which have a good handle on the current situation, show a downward trend in coverage and intensity upon arrival. Given the unfavorable timing in a stabilizing atmosphere, this downward trend seems prudent. CONSShort (with a higher RAP weight) was utilized heavily for construction of overnight PoPs. While some elevated instability does remain overnight, will keep thunder out of the forecast as it should be very isolated. Overnight lows will again will run 10 degrees below normal.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/... Cold troughing will keep isolated showers in play through the morning but will diminish by the afternoon with the upper trough axis to the east. Temperatures will again be well below normal but by Wednesday temperatures will begin to moderate as flow aloft flattens/ridges in response to a trough digging across Western Canada. Warmth and humidity are forecast to enhance via southerly boundary layer flow as that trough progresses over the Northern Plains/Upper Midwest, and precip chances escalate as ejected energy slides over the Lakes and spawns convection by Thursday. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... The aforementioned trough/associated cold front is projected across the Great Lakes and Upper Ohio Regions next weekend. Precip is thus likely but temperature in the wake of the system is expected to remain near the seasonal averages given the lack of amplitude in the progged flow pattern. && .AVIATION /22Z MONDAY THROUGH SATURDAY/... Prevailing VFR with diurnal cu expected today as we remain in the cold upper trough. Scattered showers and a few thunderstorms are possible both this afternoon and again on Tuesday with the passage of upper level shortwaves within the trough. Confidence is highest north of PIT so this is where vicinity mention will be made. Restrictions will be brief, if a shower passes overhead. Otherwise, MVFR cloud deck may be possible, again with greatest confidence up north, in the morning hours before lifting with expected mixing tomorrow afternoon. Wind gusts to 20kts are possible both afternoons. .OUTLOOK... Next chance for widespread restrictions comes with the approach of frontal boundary at the end of the week. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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