-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPBZ 251937
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
337 PM EDT Thu Apr 25 2024

.SYNOPSIS...
Mostly dry weather and a warming trend is expected through
Monday save chances of isolates showers or storms Saturday and
Sunday afternoon.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
KEY MESSAGES:

- Freeze warnings and frost advisories are in effect for
  portions of the area, beginning at midnight.

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Mundane weather will persist as the area sits underneath a
subsidence inversion in a weak pressure gradient. For this
reason, winds are expected to remain calm to light through the
near term.

A weak 850mb meso-low has been observed across southwest
Pennsylvania, allowing weak low-level convergence and moisture
pooling in the area just south of I-80. This has allowed
stratocumulus decks to persist for much of the day as mixing has
attempted to erode them. The current thinking is that most
cumulus will dissolve with sunset, but patches of stratocumulus
may linger in the aforementioned area overnight. Low-
probability clouds are also possible in the Laurels with
upsloping.

Areas that are clear at this point will likely remain clear and
there is a high probability that low temperatures tonight will
under-perform guidance, thus, adjusted towards the NBM 10th
percentile with calm winds. Should clouds linger a bit longer,
temperature will likely run higher than the forecast.

Frost advisories were hoisted based on the areal extent of 36
degrees or lower across a forecast zone after adjusting
nocturnal temperatures down. The same goes for freeze warnings;
there is a high probability of a freeze for Forest, and a
moderate probability of a freeze for Venango, Clarion, and
Jefferson PA. In these zones, calm winds and clear skies are
high probability.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
-- Changed Discussion --
KEY MESSAGES:

- Dry and warmer through Friday
- Showers and possible thunderstorms return Friday night into
  Saturday with a warm front

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The surface high pressure will migrate to the east for Friday,
with mostly clear skies for much of the daytime hours. As
surface southeast flow accelerates with pressure gradient
increases, temperatures will bounce above normal once again.

Friday evening and overnight, clouds will increase as cirrus
decks advect overhead. Thereafter, a warm front will progress
through. Precipitation timing and amounts have trended slower
and lower since the last update. Fumes of elevated instability
are possible, thus a rumble of thunder could not be ruled out as
it passes through Saturday morning. Even the 90th percentile is
only around 0.25 inches of QPF.

A moisture and temperature push is expected behind the warm
front, with a chance of isolated afternoon showers and/or
thunderstorms. Precipitation chances taper overnight. Because of
the passing warm front from the west, daytime highs will range
from above average in eastern Ohio to near/below average in
central Pennsylvania.
-- End Changed Discussion --

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
KEY MESSAGES:

- Warm with minimal chances of afternoon thunderstorms Sunday
  and Monday.
- More widespread showers and possible thunderstorms with a
  Tuesday cold front.
-------------------------------------------------------------------

Model ensembles continue to indicate the strongest riding across
the Upper Ohio Valley region Sunday and Monday. Sunday should be
mainly dry under the ridge, with warm air aloft limiting
convective potential. Still, an isolated afternoon storm or two
is possible, mainly north of Pittsburgh, where another vort max
moves across southern Ontario on the northern periphery of the
ridge.

Similar conditions are expected Monday. The ridge axis is
expected to shift slowly eastward later Monday, with slightly
better chances for afternoon showers and thunderstorms late in
the day as a shortwave trough and associated surface cold front
begin to approach from the Midwest.

Temperatures mainly in the 80-85 degree range (outside of the
higher terrain) are expected Sunday and Monday with a 1000-500
mb height of 582 dm, and 850 mb temperatures ranging from 12-14
deg C. Cooler, but still above average, temperatures should
return Tuesday behind the front.

Showers are likely, along with a few thunderstorms, on Tuesday
as the trough and cold front cross the region. The precipitation
should end Tuesday night as the front exits.

By Wednesday, one thing is more certain; the ridge amplitude
will decrease. Clustered variability of the 500mb pattern sits
anywhere between a weak 500mb trough to a weak 500mb ridge. This
ridge breakdown may lean towards more unsettled weather.

Late next week, a central CONUS ridge may develop (shown in 3
out of 4 clusters). Should it develop, it is favored to move
east (as shown in 2 out of 3 clusters) and allow warmer-than-
normal temperatures to continue through next weekend. Some
alternate scenarios include 1) the ridge not developing,
whereby temperature would remain closer to normal in zonal flow
and 2) the ridge develops but does not move east and enforces
eastern troughing, which would keep temperatures below normal.
-- End Changed Discussion --

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
Stratocumulus continues across a significant portion of the
forecast area early this afternoon while ceilings have generally
lifted to low-end VFR (3-5kft). Some erosion is beginning to
take place along the southern border of this cloud deck per
latest visible satellite imagery as MGW/ZZV have scattered out
to mostly sunny skies. This trend should continue through the
rest of the day with most of these clouds clearing by late
evening, though some patches of scattered/broken coverage may
linger into overnight hours. Winds are light across the area and
should remain that way through the night before a strengthening
and better established southeast flow sets up after 12Z Friday.

.Outlook...
VFR conditions are expected Thursday and Friday.

The probability of showers and isolated thunderstorms increases
Friday night into Saturday which will come with increasing
probabilities for restrictions as well.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Frost Advisory from midnight tonight to 9 AM EDT Friday for
     PAZ007-013-014-020-022-077-078.
     Freeze Warning from midnight tonight to 9 AM EDT Friday for
     PAZ008-009-015-016.
OH...Frost Advisory from midnight tonight to 9 AM EDT Friday for
     OHZ039>041-048>050-057>059-068-069.
WV...Frost Advisory from midnight tonight to 9 AM EDT Friday for
     WVZ001.

&&

$$

SYNOPSIS...Milcarek
NEAR TERM...Milcarek
SHORT TERM...Milcarek
LONG TERM...WM/Milcarek
AVIATION...Cermak