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426
FXUS61 KPBZ 230940
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
540 AM EDT Fri Jun 23 2017

.SYNOPSIS...
Downpours are possible through tonight with a tropical airmass
in place. A cold front sweeping through early Saturday will
return comfortable humidity levels by the weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Rain showers associated with an upper-level shortwave are
moving through eastern OH and southwestern PA. These light to
moderate showers will slide northeast this morning following the
shortwave, bolstered by mid-level speed convergence and upper-
level divergence. This rain will continue to pre-condition much
of the Flash Flood Watch area with a quarter to half an inch of
rain, before the heavier rain chances arrive later today. With
many locations in Indiana and Armstrong Counties still impacted
by yesterday`s flash flooding including many road closures, an
Areal Flood Warning will be in effect through tonight.

This morning will feature a break in the widespread rain as the
initial wave moves east. At this point the remnants of T.S.
Cindy will be slowly moving through the lower Ohio Valley and
the cold front descending through the southern Great Lakes.
Showers and thunderstorms are expected Friday afternoon/evening
everywhere as the converging systems begin to phase near the
local forecast area. Strong ascent will meet a moisture-rich
environment to the tune of 2" or greater PWAT values. Increasing
850mb flow into deep warm cloud depths nearing 13kft will be
plenty sufficient to support tropical rain rates...causing very
heavy rainfall at times. To prepare for this, the local WSR-88D
has been modified to a tropical Z/R relationship.

High surface dewpoints will continue to fuel modest instability
with SB CAPE values progged in the 1000-1500 J/kg range. This,
along with moderate shear through the mid-levels should be
sufficient for thunderstorm development with a few strong to
severe possible. Freezing levels will be lofty, so the primary
threat will remain convective wind damage, but some veering in
the lowest 200mb and relatively low LCLs reveals that an
isolated tornado cannot be ruled out. The forecast area is
currently blanketed by a marginal risk from SPC, and a small
area of slight risk extending into our southern counties.
Possibility of severe weather would likely expand if more
clearing across our southern counties is achieved.

With very high dewpoints in place and expansive cloud deck
expected, temperatures won`t range wildly over the next 24
hours. Highs today will be near or a few degrees below average,
but the muggy conditions will prevail.
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&&

.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/...
Instability will lessen heading into the evening which will
decrease the severe threat, however, another period of moderate
rain still looks likely Pittsburgh along and ahead of the
aforementioned cold front and under the right-rear quadrant of
the jet. By Saturday morning precipitation should be east of the
ridges as drier air moves in behind the front. Saturday should
be noticeably more comfortable with highs in the upper 70s and
lower humidity. Benign weather can be expected Saturday night
with high pressure.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Sfc high pressure will remain largely in control on Sunday,
however, a shortwave passing to the north could result in
scattered precipitation along and north of I-80 during the
afternoon. A stronger shortwave will deepen the eastern CONUS
longwave trough on Monday...maintaining slightly below normal
temperatures and return chances of precipitation during the
afternoon through Tuesday morning. Upper ridging will follow...
bringing temperatures back to their normal location and
returning dry weather.

&&

.AVIATION /10Z FRIDAY THROUGH TUESDAY/...
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Most ports dropping to at least low MVFR this morning as the
low-levels saturate. An upper-level shortwave trough is
spreading light to moderate rain northeast. Most ports will
hover between low MVFR and IFR this morning with little gains
made through early afternoon.

Restrictions will likely continue through Friday as the
remnants of Tropical Storm Cindy merge with an approaching cold
front. Showers, thunderstorms, and low ceilings will be common
Friday afternoon through the evening. Low ceilings will once
again plague the region tonight as the front makes its way
across the area.

Wind will remain WSW through the period, with gusts expected
Friday afternoon.

.OUTLOOK...
Widespread restrictions are likely through Saturday morning with
the passage of a cold front.
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&&

.HYDROLOGY...
A flash flood watch has been issued for areas along and south
of interstate 70. In addition, Allegheny, Armstrong and Indiana
counties have been included, due to very low flash flood
guidance.

Meteorologically values all point to high water issues with
PWATS over two inches, warm cloud depths above 13KFT, and a
strong low level jet. GEFS M-Climate values are near or at
record levels for PWATS on return interval, and climate
anomaly.

Widespread 1.5" to 2.5" through tonight could lead to strong
rises on the Monongahela, Cheat and Ohio Rivers and their
tributaries. Slightly less is expected north of the Watch area,
but the Allegheny basin could still see a widespread 1" to 2".

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...Flash Flood Watch through late tonight for MDZ001.
OH...Flash Flood Watch through late tonight for OHZ057>059-068-069.
PA...Flash Flood Watch through late tonight for PAZ021>023-029-031-
     073>076.
WV...Flash Flood Watch through late tonight for WVZ002>004-012-021-
     509>514.

&&

$$