123
FXUS61 KPBZ 190532
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
132 AM EDT Sat Jul 19 2025

.SYNOPSIS...
Rain across northern West Virginia will diminish this evening.
Additional thunderstorms are expected Saturday afternoon into
Sunday with a warm and cold frontal passage. Flash flooding, as
well as at least isolated severe storms, are possible.

&&

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

- Lingering showers diminish this evening
- Fog development is likely overnight in areas that get heavy
  rain today.
---------------------------------------------------------------

Activity along the stalled boundary south of the Mason-Dixon
will continue to weaken this evening with only
scattered/isolated activity in the ridges by 06Z as instability
diurnally decreases. Lingering low-level moisture and daytime
rain will led to some fog develop tonight, especially over the
ridges and locations in WV that received the heavier totals.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH SUNDAY NIGHT/...
KEY MESSAGES:

- The front likely returns north on Saturday, bringing a risk of
  heavy rain and flooding at least to areas south and west of
  Pittsburgh.
- A more isolated flooding threat is possible Sunday with a cold
  frontal passage.
- Severe potential for Saturday and Sunday, with damaging wind
  gusts being the most likely threat.
----------------------------------------------------------------

The boundary will begin to lift northward across the region again on
Saturday, as a shortwave trough crosses the Middle/Upper Ohio
Valley, and as surface low pressure crosses the Upper Midwest into
Lower Michigan by 00Z Sunday.

Trends in the CAMs suggest later timing for the bulk of the
precipitation, more towards the very late afternoon and
evening. Model soundings are suggesting some mid-level warm
air/capping that may inhibit convection until the shortwave
arrives later in the day. This late-day convection may arrive in
the form of a weakening MCS in Ohio, at a time when instability
may be diurnally decreasing. SPC has pulled the day 2 slight
risk a bit further west, essentially out of the forecast area,
while maintaining a marginal risk over areas north and west of
MGW. This seems reasonable, as increasing low- level flow and
20-30 knots of deep shear may support storm clusters capable of
damaging wind gusts mainly, with a lesser risk of large hail.

The flooding risk still exists as well given the likelihood of PWATs
rising above the 90th percentile once again by later
Saturday/Saturday night, with soundings supporting warm rain
processes especially in eastern Ohio. Interestingly, HREF
probabilities of greater than an inch of rain over 24 hours are
fairly suppressed through Saturday night, maximizing in the
30-50% range west of the Ohio River and south of I-70. While the
best flood risk may exist to the southwest of Pittsburgh
through tomorrow night, think that these probabilities may be a
bit underdone. While storm motions will be higher, the
potential for heavy rates and an already saturated ground will
keep the flood risk elevated.

Sunday will feature a cold frontal passage as the Michigan
surface low tracks into New England. Ensembles suggest a severe
threat perhaps as early as the late morning hours and into the
afternoon, with potential for 1000-1500 J/kg of surface-based
CAPE overlapping with 30-40 knots of deep shear, mainly from
Pittsburgh on south. This supports the day 3 marginal risk in
this area from SPC for mainly a wind threat. The flooding risk
will likely be confined to areas where east-west training may
occur ahead of the advancing front.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
KEY MESSAGES:

- Building high pressure aloft may provide relatively dry
  weather early next week.
- Heat and humidity begin to increase during the middle part of
  the week.
- Shower/thunderstorm chances increase Thursday and Friday.
-------------------------------------------------------------------


There is good confidence among the ensembles that strong ridging
builds over the Mississippi Valley and into the eastern CONUS next
week. Along with crossing high pressure to our north, a mainly
dry pattern appears to extend into Tuesday, and possibly into
Wednesday, with the potential for subsidence/warm air aloft to
suppress convection. Of course, this will also lead to above-
normal temperatures. NBM probabilities of 90+ highs increase to
40-70% over much of the area by Wednesday, and then 50-80% on
Thursday. Combined with high dewpoints, heat risk is set to
rise by the end of the forecast period.

Shortwaves riding the top of the ridge may begin to suppress heights
slightly by the Thursday/Friday period.  This could lead to better
rain chances during this period. Longer-range machine learning
guidance suggests an uptick in severe storm potential as well, which
makes sense given the amount of instability/moisture that may be
available.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
Early morning satellite imagery and surface observations depict
a large MVFR to low VFR stratus deck near the stalled surface
boundary that is likely to persist through 14z. Localized top
down moistening and weak fog advection may allow for periods of
IFR, notably at HLG/MGW, but persistence is more likely to
prevail. Greatest uncertainty is whether VFR decks clear out
near FKL/DUJ; satellite trends suggest that will which should
allow for rapid low stratus/fog development.

Diurnal heating/mixing combined with slight lifting of the
boundary will slowly improve and eventually erode stratus decks
between 15z-23z. Approach of a shortwave may induce an isolated
shower/thunderstorm SE of Pittsburgh during the afternoon, but
probability of terminal impact is too low to mention.

Hi-res models suggest an MCS-like system may approach the region
after 00z from the western Great Lakes. Timing and its ability
to maintain are highly uncertain, but it may pose risk for
drastic visibility restrictions in heavy rain and gusty, erratic
winds.

Outlook...
Widespread MVFR/IFR restrictions are favored post-convective
system Saturday night into Sunday morning as moisture pooling
continues. The passage of a surface cold front underneath NW
flow Sunday afternoon/evening may offer additional thunderstorm
chances that feature gusty winds.

Ensemble models are confident in high pressure promoting dry
weather Monday and Tuesday, with subsidence aiding a prolonged
period of VFR.

&&

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

&&

$$

SYNOPSIS...Rackley
NEAR TERM...Rackley/CL
SHORT TERM...CL
LONG TERM...CL
AVIATION...Frazier