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FXUS61 KPBZ 251905

Area Forecast Discussion
National Weather Service Pittsburgh PA
305 PM EDT Thu May 25 2017

Passing low pressure will provide rain chances into Friday
morning. Approaching low pressure will keep precipitation
chances in the forecast for the holiday weekend, with Sunday
projected to be wetter than Memorial Day.


Vertically stacked low will swing across the region tonight.
More organized moisture and lift has moved north of the region,
but steep low-level lapse rates have started to produce popup
showers especially close to the low. Expect this trend to
continue through the afternoon and into the evening, with likely
PoPs appropriate. with one or two thunderstorms possible in the
generally low instability. Region is still scraped along the 
ridges by a marginal risk of severe thunderstorms according to 
SPC. Think that this threat is minimal given the marginal 
instability and expected weakening shear profiles.

PoPs will slowly decrease through the night with the loss of
instability, although the presence of the low and a shot of lift 
will keep showers going. An overnight low level jet may produce
some 25-30 MPH gusts along the ridges overnight, with lesser 
values elsewhere. The ongoing mixing will keep overnight 
temperatures a few degrees above climatology.

Showers should pull east with the low by Friday afternoon,
giving our region a brief dry interlude, although some clouds
should linger. Warmer temperatures are expected with a bit more
sun, with near-normal values in southeast Ohio but still below-
normal to the east.


PoPs will increase again starting Friday night in increasing
isentropic lift ahead of an advancing warm front. Model
agreement on precipitation placement appears to be improving,
but intensity is still a bit in question. Will continue with
previous idea of a north/south gradient in rain chances, highest
close to the front, with better thunder chances there as well.
The front will likely become quasi-stationary across West
Virginia. Passage of a mid-level wave will keep precip chances 
going through Saturday, before tapering a bit Saturday evening. 
At this time, it still appears that the best severe risk will 
lie to our south, in better instability and shear south of the 
stalled boundary, but this will need to be monitored for any 
model variances.

Approaching surface low pressure will push a cold front towards
the region for Sunday, with an attendant increase in showers and
thunderstorms. Kept likely PoPs going. Severe risk will likely
be mitigated by the presence of morning clouds/showers limiting

Temperatures will rise to near or even slightly above normal
levels by the end of this period.


A fairly broad Great Lakes/northeast U.S. trough will be in
place through this period. Shortwaves rotating through the
trough will keep periodic shower chances in the forecast each
day, with a somewhat diurnal pattern to the rise and fall of the
numerical values. Near to slightly below normal temperatures 
can be expected in this pattern.  A transition to a more zonal 
regime may begin by the end of the period, with lessening rain 


Upper low continues to sit and spin across eastern Ohio. A wave  
of showers has moved through the forecast area this morning, and
will rotate through the area once again this evening into the
early morning hours. Some scattered showers will remain in
between the waves, and cannot rule out a chance of an isolated
thunderstorm, although confidence/coverage is low.

In between the waves, many locations from Pittsburgh to the
south and east should have at least a few hours of VFR 
ceilings, although ZZV/BVI/FKL/DUJ are expected to remain close 
enough to the bands of steadier rainfall for ceilings to remain 
IFR/MVFR. All terminals will drop to IFR, if not LIFR ceilings 
overnight in steadier rain, and low clouds will continue well 
into Friday.

Showers continue through much of the period with episodic



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