839
FXUS61 KPBZ 280601
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
201 AM EDT Fri Jun 28 2024

.SYNOPSIS...
High pressure building across Pennsylvania and New York tonight
will bring quiet weather that should last into Friday. A warm
front will lift north Friday night with increasing chances of
showers. Showers and thunderstorms are then expected Saturday
and Saturday night as a cold front advances south into the warm
and humid airmass that will be in place across the Upper Ohio
Valley.

&&

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

- Dry weather and light wind expected overnight.

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No significant changes needed to going forecast. Previous
discussion follows...

Surface high over Michigan should build across SW Ontario this
evening and then New York and Pennsylvania later tonight. Quiet
weather will continue as a result. Lows will be near normal with
850 mb temps in the 12-14C range.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/...
KEY MESSAGES:

- Dry weather continues.
- Temperature rises above normal again Friday.

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Surface high pressure transitions over New England and heights
rise ahead of the next upper-level shortwave trough. Heights
will end up around 70 meters higher than this evening, and 850
mb temps are forecast to rise to about 18C.

Positioning of the high will support weak warm, moist advection
amid mostly clear skies to raise area temperature about 5
degrees above the daily average solidly into the 80s. Broad
ascent may increase mid- to high-level clouds and even offer
low probability of showers Friday night as a warm front
approaches. Precipitable water is shown to increase to about
1.8" by late Friday night, supporting the potential for
precipitation.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
KEY MESSAGES:

- Shower and thunderstorm chances return Saturday into Sunday
  with the next low pressure system.
- Severe and Flash Flood threat returns Saturday.

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Broad ascent within warm, moist southwesterly flow ahead of the
main upper-level trough will support increasing shower and
thunderstorm probabilities starting early Saturday morning as
the associated sfc low moves across the upper Great Lakes.
Saturday afternoon and evening is likely to be active with a
crossing shortwave trough and a cold front approaching from the
west.

Severe weather will once again be a possibility as increasing
mid-level flow overspreads an increasingly moist warm sector
with 850 mb theta-e increasing into the 345-350K range. Latest
ensembles show CAPE values from 1000-2000 J/kg with effective
shear ~30-40 kt. Machine learning output shows 5% probs for
both wind and tornadoes, which is not surprising looking at
forecast hodographs.

Flash Flooding will also be a threat with anomalously high
PWAT (>2"), abundant buoyancy, and warm cloud depths >13kft,
which would all lead to very efficient warm-rain processes, and
torrential downpours in storms. Corfidi vectors show the
classic ridging pattern over Ohio with values decreasing to 5-10
knot range during the evening, indicating potential for slow-
moving or backbuilding storms with heavy rainfall. WPC has
noted a >5% risk for excessive rain while machine learning
output highlights >15% risk.

Dry weather and seasonable temperature are likely by late
Sunday into next week as the upper trough axis moves east and
high pressure builds in from the western Great Lakes.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
Patchy fog could not be ruled out in the morning, particularly
for river valleys, although light winds, increasing upper
clouds, and dew point depressions of a few degrees should keep
widespread mentions minimal. Probabilities of MVFR vis only max
out at FKL at 30%.

Any fog will dissipate into the day and winds will veer south-
southeasterly with the development of VFR diurnal cu. Upper
clouds increase overnight with some small chances of rain west
of the mountains, primarily after 04Z.


.Outlook...
Restrictions are likely Sat and Sat night with showers and
thunderstorms ahead of and along a crossing cold front. Some
storms may be severe. VFR returns Sun under high pressure and is
likely to persist Mon and Tue.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.

&&

$$

SYNOPSIS...Craven/Kramar
NEAR TERM...Craven
SHORT TERM...Craven
LONG TERM...Craven
AVIATION...Milcarek