Area Forecast Discussion
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FXUS61 KPBZ 231503

Area Forecast Discussion
National Weather Service Pittsburgh PA
1103 AM EDT SAT JUL 23 2016

Hot humid weather is forecast for into early next week along with
intervals of scattered thunderstorms.


Weak boundary, indicated mainly from a wind shift in surface obs,
is bisecting the CWA this morning. In the vicinity of this
boundary some cumulus is starting to develop. This may be the
focus for the development in widely scattered thunderstorms today,
as is progged by the hi-res models. In addition, the help of a
passing shortwave in northwest flow, may further provide lift for
a thunderstorm or two. Opted to expand low chance pops a bit
further north, based on the model and satellite/surface analysis.

Otherwise, most locations should exceed 90 today. Dry air through
the entire column is present north in NY where dewpoints are in
the upper 50`s. The Buffalo sounding also shows this dry air at
both the surface and aloft. This will be advected toward the
region as the shortwave trough approaches, which should limit both
cloud cover and decrease dewpoints over the northern half of the
region this afternoon. While this should bring a break in the
humidity, it could also stand that any mixing may bring
temperatures up above 90 faster than locations to the south, where
the warmer dewpoints and cloud cover remains. Have made little
change to temperatures through the afternoon and with the 70
dewpoints likely to hold over our southern counties until late
today, have opted to keep the heat advisory as is, as indiceswill
still be very near 100.

Model guidance suggests that these drier dewpoints will never
fully make it across the entire region before southerly flow
returns ahead of the next front Sunday. But, this should be
sufficient enough to provide a cooler night, for the northern
half of the region, than previous nights.


A passing shortwave ridge aloft will keep the forecast area mostly
dry through the afternoon Sunday. Only maintaining a slight chance
of showers/thunderstorms during the evening as the ridge axis shifts
east and flattens due to a weak wave passing through the southern
Great Lakes.

Ample low-level moisture will linger, keeping dewpoint temperatures
in the mid to upper 60s. This moisture, combined with hot
temperatures, will again have heat indices in the mid to upper 90s
for most locations west of the Ridges. Only have a few counties
flirting with 100, and those counties already have a Heat Advisory
for Saturday, so opted to maintain the Sunday HWO mention for now.

An upper-level trough will approach from the west Monday, dragging a
weak cold front behind it. This will be the impetus for the best
chance of rain over the next several days. Mid-level temperatures
will remain fairly homogeneous Sunday into Monday, but strong
warming at the surface and lingering high dewpoints will fuel
instability ahead of the trough Monday afternoon. This, along with
modest vertical shear, should be enough for a few strong
thunderstorms to develop, but a widespread severe threat is not
expected at this time. Model soundings do suggest efficient rain
production with any thunderstorms Monday as the warm cloud layer
will extend above 10kft and PWATs approaching 2.0", which is well
above average. The boundary will sag south of the area Monday night,
with gradually declining rain chances into Tuesday morning. tax


A weakening surface boundary will stall just south of the forecast
area Tuesday. Models differ slightly on how far north afternoon
thunderstorms activate along the boundary Tuesday and Wednesday.
Kept slight chance PoPs relegated to south of the Mason-Dixon line
Tuesday afternoon, but high pressure building at the surface across
our north, results in a mostly dry forecast. Dry weather is expected
to last into Thursday morning, as upper-level flow goes zonal. High
pressure will start to break down towards the end of next week as
broad troughing begins aloft. This will bring periodic showers and
thunderstorms back to the forecast through the early part of next
weekend. tax


vfr conditions today. In airports from KZZV to KPIT to KLBE and
south, there is a chance of an isolated shower after 18Z but will
be very widely scattered.

Restrictions will be possible late Sunday and Monday with the
approach and passage of a weak cold front.


OH...Heat Advisory until 8 PM EDT this evening FOR OHZ048-057>059-
WV...Heat Advisory until 8 PM EDT this evening FOR WVZ004-012.


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