fxus61 kpbz 141928 

Area forecast discussion 
National Weather Service Pittsburgh PA 
328 PM EDT Tue Aug 14 2018 

scattered showers and thunderstorms are expected today under an 
upper level low. Dry weather should return Wednesday under 
building high pressure before approaching low pressure returns 
rain chances for Thursday. 


Near term /until 6 am Wednesday morning/... 

An unstable and uncapped environment resides over the County Warning Area on 
the backside of upper level low churning over eastern New York. With 
convective temperatures breached most everywhere (other than far 
eastern counties still under overcast), expect nacient shower 
development to quickly become more numerous through the 
afternoon. Kpit 12z sounding probably underestimated the degree 
of instability present given the dry air entrainment from 
upstream (as evidenced by eroding of earlier cloud cover and 
Kiln sounding), although still considerably less than 
yesterday. Still don't see sufficient convective cloudy depth 
above the freezing level, which should not only limit lightning 
frequency and any threat of hail, but do not see sufficient 
dcape to warrant a severe threat this afternoon. Although warm 
rain processes will dominate, cells should move steadily to the 
southeast and thus flooding threat is minimized. 

Shower/thunderstorm threat should end quickly after 00z due to 
departing forcing and the loss of daytime heating. Skies should 
clear quickly, and with residual moisture present, patchy to 
potentially widespread fog development looks likely if winds 


Short term /6 am Wednesday morning through Wednesday night/... 

Fog will rapidly dissipate after 12z with daytime mixing and a 
transient shortwave ridge will bring a warm and dry day to the 
area tomorrow. 


Long term /Thursday through Monday/... 

Elevated warm front will lift across ern Ohio/WV/ern PA early 
which may provide an early threat for showers/storms during the 
early morning hours. Otherwise, more widespread precipitation 
will arrive Thursday afternoon with the first in a series of mid 
level impulses that will eject through a broad trough over the 
Midwest. With surface pressure fields weak and the primary jet 
streak situation over Canada, it's expected that several rounds 
of showers and thunderstorms will remain focused over the area 
through Friday. 

Precipitation chances are a bit lower Saturday as the better 
forcing shifts from the Tennessee Valley to New England, but 
persistent troughing aloft suggests that rain chances aren't 
zero. Sunday looks much more promising as a completely dry day 
headed into early Monday before another in a series of Pacific 
troughs reaches the area. 


Aviation /19z Tuesday through Sunday/... 
medium confidence forecast. Fog or low clouds could be lower 
than forecast during the 8z-14z time window. 

More of the same with scattered showers around the upper level 
low that continues to move slowly east. Coverage of showers 
warrants more vc mention especially for lbe, fkl, and duj which 
are closer to the center of circulation. Farther west, removed 
mention at zzv and hlg given limited instability and aerial 
coverage of showers based on recent high resolution models. 
Cigs will be teetering on the cusp of MVFR/VFR through the 
afternoon as waves of low level moisture will be pivoting north 
to south. 

Activity will quickly diminish between 22-24z giving way to VFR 
weather /scattered high clouds/. The primary forecast challenge 
is how and where sub VFR fog develops? Best shot appears to be 
lbe, fkl, hlg, and duj where low level moisture will be more 
abundant. Brought those airports down to 2-4sm in the 9-14z 
period. If no fog develops VFR weather will carry through the 
morning hours Wednesday. 

Winds will be less than 10kts out of the west - southwest 
through the period. 

sub VFR weather is possible Thursday evening into Friday 
morning with a cold front. 


Pbz watches/warnings/advisories... 

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