Area Forecast Discussion
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FXUS61 KPBZ 200121

Area Forecast Discussion
National Weather Service Pittsburgh PA
921 PM EDT Fri Aug 19 2016

Scattered showers and thunderstorms are forecast through Saturday.
A cold front will bring better rain chances Saturday night into
Sunday. Behind the front, dry weather and much less humidity are
expected for the first half of next week.


As of 9:15pm, only thunderstorm remaining in the forecast area is
in the I-80 vicinity and appears to be weakening. Once showers in
this area diminish, expect that conditions should be dry for the
rest of the night, considering the upstream shortwave moving into
the region from western Ohio is not currently producing any rain.
However, the shortwave should bring some additional clouds later
tonight. 850hpa temperatures are slightly warmer today than
yesterday, so temperatures were bumped up a degree.

Much of the same is expected on Saturday, with moisture increasing
in southerly flow ahead of the approaching cold front. Again, lift
is not overly impressive and warm air aloft may be enough to cap
convection for much of the day. Therefore, did not go any higher
than slight chance pops, save for the ridges, for much of the day.
Temperatures should stay close to values today, minus a degree or
two with more cloud cover.


The main player this period remains the mid-level trough moving
from the upper Midwest across the Great Lakes, and it`s leading
cold front. Decent model agreement on the depth and timing of the
system. A plume of 1.75 to 2 inch precipitable water precedes the
front, along with isentropic lift on the 305/310K surfaces. Think
categorical PoPs are appropriate for most of the CWA after 06Z
Sunday. Think that the best potential for lift remains north of
the CWA in the deeper part of the trough. The front reaches the
Ohio River vicinity by 12Z Sunday, and sweeps eastward from
there, exiting to the east by mid- afternoon. Given the speed and
timing, do not believe that the system provides either a flooding
threat or a severe weather threat. A general one to two thirds of
an inch of storm total rainfall can be expected, although a few
locations could see a bit more. Made only minor modifications to
Saturday night/Sunday temperatures, as the diurnal range was
already appropriately small.

A few showers may linger behind the front into Sunday evening,
especially north of Pittsburgh, before the 500 mb trough axis
moves through. Otherwise, skies will clear and dew points will
begin to drop off, signaling a welcome air mass change. Monday
morning low temperatures will be roughly 10 degrees cooler than
Sunday. A noticeably fresher environment will be in place Monday
afternoon, along with plenty of sunshine, as a sprawling surface
high builds in.


The dry pattern will continue through Wednesday night as the
surface high slowly moves east. Mean troughing aloft will
transition to mean ridging by Wednesday, which suggests a warming
trend. Still, dewpoints should remain in the comfortable range
through then. More humid weather arrives Thursday in southwest
flow. The next front approaches in the Thursday night/Friday
period, with the next chance of showers and thunderstorms.


FKL and possibly DUJ are the only sites that appear to have much
of a chance for restrictions as a result of showers/thunderstorms
during the evening hours. After midnight, it appears some fog may
be possible with plenty of low level moisture, but lingering high
clouds may limit it`s extent. Generally stayed more optimistic
than LAMP and NAM guidance based on crossover temperatures and
model soundings.

Outside of fog, VFR is anticipated again on Saturday with limited
coverage of showers.

The next chance for widespread restrictions will come with a
strong cold front Saturday night and Sunday.




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