Area Forecast Discussion
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FXUS61 KPBZ 211017

Area Forecast Discussion
National Weather Service Pittsburgh PA
617 AM EDT THU JUL 21 2016

Hot temperatures are expected today, but humidity will be
tolerable. A more steamy airmass is forecast for Friday and the
weekend, along with periodic thunderstorm chances.


Other than updating near-term hourly temperatures, no updates were
needed at 615 AM.

Previous discussion...

Surface high pressure will slide to our south during the day. 500
mb heights will reach their peak during the day, and with still
low dewpoints and dry soil, today will likely feature the highest
temperatures out of the next several days. The difference in later
periods will be higher dewpoints, resulting in higher heat
index/apparent temperature values than today. Given the pattern
and favorable antecedent conditions, kept the idea of
temperatures higher than most models would suggest.

Tonight, an approaching shortwave will start the process of
locally mitigating the upper ridge. Expect at least a few showers
and thunderstorms to reach the forecast area prior to sunrise,
although the initially dry airmass may hinder the southward
progress of rain. PoPs may need to be lowered in subsequent
updates. Kept low temperatures on the warm side given slow cloud
increase and better mixing than tonight.


A weak upper-level wave will pass north of the area Friday morning,
with a chance of showers and thunderstorms, mainly north. The main
shortwave timing has been consistent, passing by 12z, but a
transition to a northwest upper-level flow regime will open the door
for additional showers and thunderstorms through Friday. Fueled by
high dewpoints nearing 70, instability will increase through the
afternoon. If thunderstorms can develop under mesoscale influences,
Friday afternoon, a few could be strong. The marginal risk has been

A bit of model divergence heading into the weekend, as most guidance
shows high pressure re-gaining control of the area by Saturday. The
00z NAM continues to hold the surface high back to the northwest,
ultimately streaming additional upper-level waves across our north.
Will continue to monitor this trend in the NAM, but for now, opting
to carry a drier forecast with temperatures soaring well above
average. Hot temperatures and dewpoints nearing 70s will lead bring
uncomfortably warm conditions for the weekend.


Ridge of high pressure will temporarily break down beginning of
next week as a system dives into the Great Lakes. This will bring
rain chances back to the area Monday, but the progressive nature
of this system will limit overall precipitation. High pressure
re-establishes by middle of next week with drier weather again
expected. Zonal flow aloft will bring the next disturbance back to
the area by the latter part of next week. After the hot weekend,
temperatures will moderate some, but will remain above average
through the extended period.


VFR conditions were maintained through the TAF period, although
restrictions cannot be ruled out towards the end north of PIT. No
issues today with few clouds and light winds. A shortwave will
start to approach late tonight and bring an increase in clouds,
and possibly spread a few showers or storms into the area after
06Z. Handled with VCTS mention for now. Any ceilings towards the
end of the period should remain around 5000 feet.

Scattered restrictions in thunderstorms are possible Friday
through Monday.




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