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540
FXUS61 KPBZ 250035
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
835 PM EDT Fri May 24 2024

.SYNOPSIS...
Isolated showers are expected south of Pittsburgh this evening.
The risk for more widespread showers and strong to severe
storms increases Saturday afternoon/evening. Sunday is expected
to be mostly dry under high pressure.

&&

.NEAR TERM /UNTIL MIDNIGHT TONIGHT/...
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KEY MESSAGES:

- Isolated showers and storms near and south of I-70 will
  continue through the evening, before ending after midnight.
- Above-normal overnight low temperatures continue.
  _____________________________________________________________

Isolated to widely scattered showers and a few thunderstorms
continue near and south of I-70, near a weak but still-present
surface boundary and in an area of 1000-1500 J/kg of surface-
based CAPE. Flow in the column is weak, and warm air aloft is
capping the storms at about 20-25k feet. No severe weather is
anticipated, but the strongest cells could produce small hail,
gusty wind, and localized downpours (perhaps 0.5-0.75 inch in
isolated areas). Coverage will drop off after midnight given
increased convective inhibition, and quiet weather will remain
through sunrise. Overnight low temperatures will remain roughly
10 degrees above normal.
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&&

.SHORT TERM /MIDNIGHT TONIGHT THROUGH SUNDAY/...
KEY MESSAGES:

-A crossing shortwave will return the risk of strong to severe
 storms Saturday afternoon/evening; hail, damaging wind, and
 excessive rainfall will be the main threat.
 _____________________________________________________________

A weak ridge will continue to break down across the Ohio River
Valley early Saturday as an ejecting low out of the northern
Dakotas tracks into the Great Lakes. With a flux of low-lvl
moisture Saturday morning, a few showers and storms may evolve
along the moisture boundary. However, scattered to widespread
organized convection is expected to develop mid-afternoon as a
cold front slowly advances into Ohio. During peak heating, where
temperatures will range from low to mid-80s and low-lvl
moisture is widespread across the region (dew points in the
mid-60s), MUCAPE values will climb between 1500J/kg to 2000J/kg
just before sunset. There will be small window of opportunity,
based on atmospheric profiles, that hail and strong downdrafts
could develop in a few storms.

By 8pm to 10pm, ongoing convection will likely shift
from hail/wind threat to a excessive rainfall threat and areas
that have training storms with prolong periods of 2 to 3 inch
rainfall rate will be vulnerable to flooding. Flood-prone and
urban areas will need to be closely monitored into the overnight
hours. Hi-Res models suggest the probability of all threats
will be low between 2am to 4am Sunday.

While precipitation wraps up across the Ohio River Valley, all
eyes are focused on a new low pressure system developing in the
Great Plains early Sunday morning. Hi-Res models and long range
models have been consistent on the track of the low advancing
through the Great Lakes region by late Sunday/early Monday
morning. The GFS and some of the Hi-Res models have some
discrepancy on how far north moisture will advance under
southwest flow Sunday night into early Monday morning. Vertical
wind shear will not be the primary problem with organized
convection, it is mainly a destabilization issue. The Storm
Prediction Center has portions of eastern Ohio under a Marginal
threat for now, however the threat may shift further north,
towards Pittsburgh, if the CAMs come to an agreement on the
overall pattern in the next 24 hours. Along with damaging wind,
hail, and/or tornadoes, flooding will once again be a concern;
especially to hard hitting areas from anticipated convection on
Saturday.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
KEY MESSAGES:

- The potential for strong to severe storms may continue into
  Monday.
- Near normal to below average temperatures are expected under
  an elongated trough over the Northeast.
  ____________________________________________________________

With ensemble members suggesting a slow progression of the
upper-level low over the Great Lakes Sunday into Monday, the
threat for strong to severe storms may continue for portions of
the region.

Long range suggests a shift to a cooler pattern by the middle
of next week as upper troughing develops over the Great Lakes.
Expect temperature to fall below the seasonal average, with
Wednesday potentially being the transition day from shower
activity to dry weather.

&&

.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
VFR expected through at least 15z Saturday under the influence
of high pressure, with increasing southwesterly surface wind
Saturday afternoon.

Though a very isolated shower/thunderstorms can`t be ruled out
through 06z near MGW/ZZV, a stabilizing environment should keep
probabilities of occurrence/impact low enough for mention.
Shortwave passage Saturday afternoon and evening will offer more
widespread thunderstorm chances (lowered vsbys and gusty,
erratic winds possible). However, uncertainty remains high as
initiation, timing and evolution are fairly dependent on
progression of convective activity across the lower Ohio River
Valley tonight. Tempos reflect highest probability of
occurrence, but storms as possible as early as 15z and even at
the end/after the TAF period.

.Outlook...
High pressure and subsidence should promote VFR and dry weather
late Saturday night into Sunday. Fog may develop before dawn
Sunday in rain-soaked locales that experience overnight
clearing.

Thunderstorm probabilities increase overnight Sunday into
Monday as a more robust low pressure system moves through the
Great Lake region. A pattern shift thereafter will introduce
periodic precipitation chances and potential for more prolonged
cig restrictions.

&&

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

&&

$$

SYNOPSIS...Hefferan
NEAR TERM...Hefferan/CL
SHORT TERM...Hefferan/22
LONG TERM...Hefferan
AVIATION...Frazier