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NWS Area Weather Forecast Discussion
County Warning Area [CWA]: PBZ
Regional NWS Weather Office: Pittsburgh, PA

FXUS61 KPBZ 261744

Area Forecast Discussion
National Weather Service Pittsburgh PA
144 PM EDT Tue May 26 2020

A strong area of high pressure will maintain dry weather for the
area through Thursday with well-above average temperature. Rain
chances come back Thursday morning and again on Friday with a series
of low pressure systems. Cooler and drier weather will then return
for this weekend.


GOES satellite imagery and forecaster observation shows a virtually
cloudless sky across the NWS Pittsburgh Forecast Area as of 120PM--
which is quite a rare feat for one of the cloudiest areas in the

A rather amplified ridge remains in place across the eastern CONUS
with the axis of this 590dam ridge just to our east. Subsidence and
very warm mid-level air has essentially suppressed any convective
clouds thus far today. With plenty of heating and just enough boundary
layer moisture, a CU field may still develop over the next few
hours... but updrafts will have difficulty sustaining/growing. A
stray shower cannot be completely ruled out, but the
coverage/probability is quite low.

As far temperature, temperatures well into the 80s this afternoon
(70s for the mountains and around 90 for the city) will fall back
into the 60s at night.. but may plateau towards dawn as high clouds
spread across the Upper Ohio Valley.


Similarly warm and humid conditions will continue through mid-week
as the amplified synoptic pattern remains in place with the Upper
Ohio Valley (~the Pittsburgh forecast area) located in southerly
flow between an anomalously strong ridge off the east coast and a
stacked upper/mid-level low across the Mid-South.

For Wednesday, an upper-level trough originating from the southeast
will rotate around the aforementioned low and move into the Ohio
Valley. While the sensible surface response and precipitation
features will be focused towards Indiana, models are signaling an
associated upper-level cloud deck crossing the region in the morning
hours that will then deepen through the day with the approach of
another, more substantial, shortwave trough and associated surface
low moving northward through the Appalachians. The temp diurnal
range for Wednesday will hinge on the depth of this upper-level
cloud layer and the amount of insolation that is let through. Still,
expect a warm and humid day given the underlying summer-like

If the upper-level cloud deck is indeed as deep as some model
guidance is hinting at, am not expecting much in the way of
convective lower clouds or showers... especially with a very dry 600-
800mb layer and poor lapse rates outside of the boundary layer.

By Wednesday night, the second shortwave trough and sfc low
mentioned above will continue its northward track into the Upper
Ohio Valley. Light stratiform precipitation (perhaps initially
broken as the mid-level dry air saturates) will overspread our
southern counties after midnight and slowly lift northward through
the morning along the convergent axis on which it`s centered.

Adjusted POPs forward in time from the previous forecast based on
the latest model timing. It would appear now as if the latter half
of Thursday should be mostly dry in wake of this trough. However,
scattered, diurnally-driven showers or even a tstorm Thursday
afternoon may develop despite lack of upper forcing or strong
buoyancy in the mid-levels. Coverage will ultimately depend on how
fast that trough and associated cloud cover move out. The quicker the
sun returns, the more instability and shower/tstorm coverage we can
achieve. Conversely, if cloud cover lingers around longer... the
latter half of Thursday may remain dry with slightly cooler


Pattern flip alert. By Friday morning, northern stream troughing
will dig into the Great Lakes region and help kick the meandering
aforementioned mid-south low eastward into the Atlantic. An
attendant cold front will stretch from the surface low in the
Ontario/Quebec region southwest into the Ohio Valley. While some
precipitation may occur before the frontal rainband given the warm,
moist air, the bulk of the precipitation on Friday will occur late
afternoon and into the evening hours near/along the frontal zone
itself as it moves across the forecast area. The strongest areas of
synoptic lift will be displaced closer to the vort maxima of the
northern and southern stream troughs, with Pittsburgh in between
these. As a result, this front doesn`t look to be a big rain-maker
at this time. A marginally unstable environment may be just
conducive enough for a couple embedded thunderstorms and heavier
rain rates-- but nothing appears rather eye-catching at this time.

Precipitation should be clear of the forecast area by daybreak
Saturday as comparatively cooler, drier air filters in behind the

Each day from Saturday through Tuesday appear to be either near
or below-average as far as temperature-- or about 15(or more!)
degrees cooler than what we`ve experience this week. No major
precipitating-features seem to be present in the pattern, though
cannot rule out some light showers in this stretch as any pronounced
shortwave troughing rounding the base of the longwave trough could
produce something light.

Confidence in this extended period is greater than usual given run-
to-run consistency and agreement in the models.


Expect VFR conditions to remain in place across the area through the
TAF period as high pressure will remain the dominant weather feature.
Expect a few TAF locations to see some southerly wind gusts up to 15
knots with the max heating of the day until they subside by or just
after 00Z. Overnight, expect some mid and upper level cloud cover to
begin to enter the area. This will keep fog development at a minimum,
even over the rivers.

Outside of some early morning fog each day, no widespread
restrictions are expected until Wednesday night and the rest of the
work week.





Forecast Discussion from: NOAA-NWS Script developed by: El Dorado Weather