Area Forecast Discussion
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261
FXUS61 KPBZ 211437
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
1037 AM EDT Sun May 21 2017

.SYNOPSIS...
Rain chances increase today ahead of a cold front arriving late
tonight. Temperatures will be at or slightly below seasonal
averages for most of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Area of rain, associated with a shortwave ahead of the cold
front, will slowly move across the region through the
afternoon. With limited instability for thunderstorms expected,
the mention of widespread thunder was taken out until later
this afternoon/evening. A few embedded cells are still
possible with this first wave, given the warming over the
region with the lack of clouds early. Weak steering flow and
ample moisture will support periods of heavy rain but the lack of
strong ascent and high flash flood guidance values should
generally limit widespread flood concerns. Still, a few
localized water issues could arise in low spots or in areas of
poor drainage through late this evening.

Cold front, currently over Indiana, will slowly make it`s way
toward the region this evening/overnight. Even with decent shear
values, the timing of the front should limit available instability
for strong/severe storms.

Front should be aoa the ridges by Monday morning. With expected
cloud cover and precipitation, temperatures both today and
tonight should be just around or slightly above seasonal
averages.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY/...
The large parent low pressure system will move through the
western Great Lakes tonight, sweeping a cold front through our
area Monday morning. The bulk of the remaining rain chances will
be in the pre-dawn hours Monday, but a few showers could linger
in the Ridges through midday.

High pressure will begin to establish drier weather through
Monday afternoon, despite a broad upper-level trough holding in
the Great Lakes. Dry weather is expected to last through much of
Tuesday. Some model differences exist on the northern extent of
a system passing to our south Tuesday evening. For now, will
continue to side with the drier solutions, ignoring the NAM as a
fast and northern outlier.

Temperatures are expected to be near seasonal averages Monday
and Tuesday as we remain in southwesterly flow on the eastern
periphery of the broad trough.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
The broad trough will remain steadfast over the Great Lakes
through the latter part of the work week. A re-enforcing trough
will dig into the Midwest Wednesday, bringing increased rain
chances that will linger into Thursday night. By the early part
of next weekend, the Great Lakes trough is finally shunted off
to the east by a weak ridge building into the Midwest.
Temperatures will be at or below average through the latter half
of the week, but will begin to climb into next weekend.

&&

.AVIATION /14Z SUNDAY THROUGH THURSDAY/...
Locally gusty southeast winds to around 20 knots will be the
primary concern this morning across the higher elevation
terminals, where early day sunshine has tapped a linger low
level jet overnight.

Otherwise, an upper level disturbance followed by a cold front
will provide what should generally be two separate rain chances
over the next 24 hours.

Thickening/lowering clouds, and eventually areas of light
showers will overspread the terminals from west to east by early
afternoon. Upstream conditions suggest that pockets of MVFR
conditions will accompany this first batch of rain. For now have
removed thunder given the weak instability present in the
generally mid level forcing present for this activity.

Later this evening, a more strongly forced cold front will
arrive with the likelihood for more locally heavy rainfall and
thunderstorms in a narrow band of convection. Despite the time
of day, the front should provide much stronger forcing to
support brief downpours and thunderstorms in a narrow broken
line of convection. IFR conditions may locally accompany this
activity, although the time of year suggests that model guidance
is much too pessimistic over the 24 hour period with the
duration and degree of ceiling restrictions. Thus will maintain
an MVFR outlook in the TAF for now.

Improvement is expected later tonight (west) Monday morning (east)
as winds shift westerly and skies quickly clear.

.Outlook...
The next chance for widespread restrictions and precipitation is
expected Wednesday night into Thursday.

Bookbinder

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...None.
OH...None.
PA...None.
WV...None.

&&

$$



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