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FXUS61 KPBZ 260918

Area Forecast Discussion
National Weather Service Pittsburgh PA
518 AM EDT Tue Sep 26 2017

High pressure will bring dry and warm weather through mid-week
before the passage of a cold front heralds a return to
seasonably-cool conditions.


An increase in upper level moisture has been noted streaming
over the area for the past 12 or so hours in response to a
passing weak upper jet streak that is dynamically pulling a bit
of the blow off from Maria northward into our region. This jet
streak will exit to the east as the morning goes on today, 
yielding increasingly sunny conditions through the day after a 
start with a fair bit of high clouds. 

The aforementioned high clouds have been rather pervasive
through much of the night. This has worked to keep our
temperatures largely in the upper 60s for almost the entire 
area save for portions of central Ohio through 5 AM. A warmer 
start to the day combined with clearing with the exit of the 
weak upper jet streak will likely yield a day much like 
yesterday. Similar 850 mb temperatures, but a bit lower H5 
heights should be largely offset by a far warmer start. Thus, 
highs in a few spots will again challenge or surpass 90F, while 
most others will still jump into the upper 80s. This is 15-20 
degrees above normal. Fries


The only real highlights of the short term period will be the
passage of frontal boundary late on Wednesday and the attendant
reduction in temperatures. While timing remains very similar to
the last several runs of all model systems for a passage of the
front through the area after 18z Wednesday, consensus on layer
saturation is a bit more tenuous. Without saturation of the
lifted layer with the front, rainfall will be tough to come by. 

The overly moist NAM has continuously projected widespread
precipitation with the frontal passage, and the GFS has likewise
indicated at least modest QPF. The ECMWF and Canadian, however,
have continuously opted for a dry frontal passage. Given that
the best mid-level forcing and moisture shear off to the east
well to the north of the area, it still seems hard to believe
that widespread organized rainfall will precede this front. As 
a result, just very low-end slight chance PoPs have been 
maintained with its progression. 

Regardless of the rainfall with the front, temperatures look to
drop off quite a bit. While early in the week 18-19C will be
common at 850 mb, by Thursday, northwesterly flow will have
dropped those numbers back toward 6-7C, and this will yield a
more seasonable diurnal. Fries


As an upper ridge builds into the Great Plains, a shortwave
trough will move southeastward across the Great Lakes. Models do
seem to be latching onto boundary layer moisture increases as it
traverses the relatively warm Great Lakes. All models do now
show QPF across the area, especially northern reaches of it,
late Friday into Friday evening. PoPs were increased for this.

In the wake of the wave, high pressure returns for Saturday, 
with seasonable temperature through the weekend.


Other than localized morning fog, high pressure will maintain 
light wind and VFR through the TAF period.

Restrictions are possible with cold fronts late Wed and again 



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