Area Forecast Discussion
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FXUS61 KPBZ 260747

Area Forecast Discussion
National Weather Service Pittsburgh PA
347 AM EDT Wed Apr 26 2017

High pressure provides sunshine and very warm temperatures
today. Continued warmth is forecast for Thursday, when an
approaching front brings shower and thunderstorm chances.


Low clouds continue to linger mainly east of PIT and FKL, and
are slowly eroding from the west as ridging builds in. Expecting
some fog to develop in areas that clear before sunrise, given
the wet ground, but coverage will remain patchy overall. All of
this will mix out by later this morning.

Thereafter, quiet weather is anticipated through tonight as a
500 mb ridge ambles across. Heights will rise in response to a
digging trough across the Plains, leading to a significant
warmup today. Readings will be some 10 to 20 degrees warmer than
yesterday, with many locations reaching or topping 80 degrees.

Some high clouds may arrive later tonight, but with lower levels
remaining mixed due to an increasing tight pressure gradient,
temperatures will remain quite mild overnight, with low
temperatures around 15 degrees above seasonal norms.


Main event this period is still the ejection of the Plains
trough into the Great Lakes by Thursday afternoon. This
negatively tilted feature will push a frontal boundary across
the CWA during the late afternoon/early evening. Exact timing
remains a bit problematic, and appears to be a touch faster on
latest model runs. Have maintained mostly likely PoPs for this

The severe threat remains somewhat uncertain. While deep layer
shear will certainly be present in the forecast pattern,
instability is the main question. Given afternoon temperatures
in the lower to mid 80s across much of the area with upper 50s
dewpoints, think that instability may be sufficient to overcome
mid-level capping, which could be mitigated by mid to late
afternoon anyway as cooler 700 mb temperatures arrive. Overall,
think that BUFKIT soundings may be underplaying the potential
CAPE. SPC has expanded a marginal risk over most of our area in
the new day 2 outlook, and would not be surprised to see higher
probabilities in later updates. Will maintain the HWO mention of
severe risk.

Precipitation pulls out behind the front during the evening
hours. Dry weather returns for Friday with high pressure.
Although temperatures will moderate a bit, broad southwest flow
aloft points to continued above normal temperatures.


An active pattern is figured for the weekend into early next
week. A few shortwaves will cross in continued moist southwest
flow along the front of a broad trough, leading to rain chances
for Saturday and Sunday. Timing remains tricky, but Saturday
night currently looks to be the period with the lowest coverage
in the warm sector. Temperatures remain above normal. The
trough lifts out as a closed upper low into the Great Lakes by
Monday, pushing a fairly strong boundary across us. Given system
strength, the amount of moisture, and a possibly negative tilt
to the upper trough, strong storms appear possible. Behind this
system, quieter weather and seasonable temperatures are expected
into the middle of next week.


Biggest question overnight is fog. How much will develop and how
low will vis drop. For the most part, went with a drop at all
ports to at least MVFR, with tempo LIFR possible in fog prone
locations. This is a low confidence forecast and will be
monitored throughout the night.

Improvement to VFR is expected after sunrise with south-
southeast wind remaining under 10kts.

The next chance for general restrictions is expected with late
week low pressure.




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