000 
fxus61 kpbz 210419 aac 
afdpbz 


Area forecast discussion...updated 
National Weather Service Pittsburgh PA 
1219 am EDT Mon Aug 21 2017 


Synopsis... 
a weak upper level trough will return slight rain chances to 
the forecast today. Widespread showers and thunderstorms are 
expected with a Tuesday cold front. 


&& 


Near term /until 6 am this morning/... 
a weak shortwave trough advancing out of the Midwest should 
result in slight shower chances north of I 80 toward dawn, though 
weak forcing a lack of deep layer moisture should limit this 
potential. Otherwise, an increase in mid and high clouds is 
expected ahead of the approaching trough. Lows are expected to 
be a couple of degrees above average. 


&& 


Short term /6 am this morning through Wednesday/... 
that shortwave is the lead disturbance in a series of impulses 
which will escalate rain chances into Tuesday. As for eclipse 
viewing on Monday, local conditions are not looking as favorable 
as previous as that lead impulse is expected to at least spawn 
mid level cloudiness, and possibly some isolated convection with 
its morning to early afternoon passage. The good news is that 
at moment, weak shortwave ridging is timed to suppress precip 
during the peak time of the event. 


By Tuesday, strong low pressure is forecast to dig between the 
James Bay and Great Lakes and pull a cold front toward the Ohio 
Valley. Given model-world agreement, likely precip probabilities 
have been maintained with ramped-up severe expectations as per 
a strengthened pressure gradient and resultant wind profile. That 
potential remains slight at moment as warm mid level temperature 
will likely retard overall instability. Nevertheless, prudence 
dictates inclusion in the hazardous weather outlook, especially 
in light of the projected boundary layer warmth and moisture. 


Prefrontal trough passage is timed to end the severe threat by 
Tuesday eve, with early Wednesday frontal passage heralding 
cooler temperature for the remainder of the week. 


&& 


Long term /Wednesday night through Sunday/... 
broad surface high pressure under high-amplitude eastern Continental U.S. 
Troughing is progged to support dry weather and sub average 
temperature into the weekend. 


&& 


Aviation /04z Monday through Friday/... 
high pressure will provide prevailing VFR conditions through the 
period. A brief period of pre-dawn MVFR fog is possible at 
southern ports. 


Outlook... 
widespread restriction potential returns with a late Tue/early 
Wed cold front. 


&& 


Pbz watches/warnings/advisories... 
Maryland...none. 
Ohio...none. 
PA...none. 



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