126
FXUS61 KPBZ 261956
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
356 PM EDT Sat Apr 26 2025

.SYNOPSIS...
Heavy rain will wane through the morning hours. Drier and
cooler conditions are expected Saturday afternoon into Sunday
in the wake of a cold front. Rain chances return Tuesday into
Wednesday with a cold front.

&&

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

- Temperatures continue to fall with cold advection
- Coolest night in about 10 days
-------------------------------------------------------------------

Updated mainly focused on adjusting temperatures downward a few
degrees in the near term, as cold advection is dropping
temperatures nicely behind the earlier cold front. Adjusted
overnight lows down slightly given the quicker cooling/lower
start this evening.

While some locations in the active growing season area may dip
to the 35/36 range with a clearing sky, it is questionable if
low- level mixing will decrease to the point that dew/frost
formation becomes more likely on more than a patchy basis, as
most models maintain somewhat of a surface pressure gradient
through the night. Do not have enough confidence in this to go
with more than a few areas of patchy frost overnight, and thus
do not think an advisory is necessary at this time.

Previous discussion...

Cooler and drier air has begun to overspread the region dropping
temperatures and shutting off showers. Breezy conditions are
expected to continue through the evening hours with westerly gusts
between 20-25 mph possible. Low-level moisture will continue cloud
coverage through the afternoon.

Skies begin to scatter from west to east this evening though the
overnight period with advancing high pressure. Overnight lows are
expected to fall into the mid-to-upper 30s across much of the
region, the coolest overnight temperatures we have seen since the
17th and about 5-10 degrees below average for this time of year.

&&

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

-Rising temperature expected through Monday as the region
 remains dry.
- Marginal fire weather conditions possible Monday afternoon
  with low afternoon humidity values.
-------------------------------------------------------------------

Confidence is high for a fairly benign weather pattern Sunday
into Monday, which will feature the west to east progression of
a surface high and ridge building over the Ohio River Valley.
Despite increased insolation, the residual effects of the cold
air intrusion is expected to leave area temperature a few
degrees short of average Sunday. There is potential for frost
development Sunday night into Monday morning (light wind,
potential for strong radiational cooling), but enough cirrus
overhead amid warm advection aloft should limit development or
widespread impact concerns.

Monday will see area temperature return to above seasonal levels
as surface low veers toward a more southeasterly to southerly
direction. The combination of above normal temperature and
diurnal mixing of dry air to the surface could lead to marginal
fire weather conditions Monday afternoon before moist air
returns develop Monday evening. Current ensemble means suggest
daytime humidity minimums in the upper 20s to lower 30s; if
greater mixing of dry air occurs, RH minimums in the upper teens
to lower 20s can`t be ruled out.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
KEY MESSAGES:

- Temperatures peak Tuesday before the arrival of a cold front.
- Potential for hazardous weather if storms develop ahead of the
  cold front Tuesday afternoon into early Wednesday morning.
- Multiple rounds of heavier rain possible to end week before a
  significant weekend cool down.
-------------------------------------------------------------------

A weakening upper trough and surface low that is associated with
a potentially hazardous weather situation in the Upper
Mississippi Valley region Monday is likely to move through the
Ohio River Valley Tuesday. Confidence is high in ridging over
the forecast area ahead of the feature supporting well above
normal temperature, with the degree of heating dependent on area
cloud cover and upstream convective evolution.

Ensembles exhibit a decent agreement in timing the approach of
the upper trough axis and surface cold front late Tuesday
afternoon, with a potential passage occurring by Wednesday
morning. Uncertainty increases significantly on
shower/thunderstorm potential that models depict ahead of that
boundary due to variation in convective evolution over the
western Great Lakes. Additionally, there remains variations in
the timing/depth of the upper trough axis that could alter cold
frontal movement. Given those caveats, scenarios exist for
severe weather (favoring a damaging wind threat) between Tuesday
afternoon through early Wednesday morning based model means
showcasing up to 1000 J/kg SBCAPE and 40kts 0-6km shear. The
pattern would suggest a QLCS-type storm mode along/ahead of the
cold front, but those uncertainties will greatly influence the
convective outcome.

The pattern uncertainties continue into Wednesday as ensembles
are seemingly split on whether the front clears south of the
area (allowing high pressure to build to promote dry weather) or
stalls in the region (shortwave movement within southwesterly
flow aloft may maintain shower and low probability thunderstorm
chances through the day). More cohesion arrives late into the
week and early weekend as models peg southern plains trough to
lift northward and phase with a northern stream trough near the
Ohio River Valley to create multiple days with high
precipitation potential and mild temperature. Trough passage
(timing varies notably) will usher in notably cool air that
causes area temperature to fall below average the following
weekend.

&&

.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
WNWerly winds continue through the evening with gusts near 20 KTs.
Advancing high pressure and dry air will begin to slowly erode low-
level moisture and raise CIGs through the afternoon and evening.
Increasing subsidence is expected to trap some level of moisture
near the 2-3kft level into the overnight hours. With this moisture
trapped below the subsidence inversion some sites may experience
CIGs scattering out rather than rising back to VFR. Either way VFR
conditions are expected to return from W to E overnight with the
possible exceptions being LBE/FKL/DUJ which still sport about a 40%
chance of being MVFR by 12z Sunday. Probabilities of MVFR CIGs drop
to near 0% for these stragglers by 14z.

Outlook... VFR prevails Sunday and Monday under high pressure.
Restrictions, and showers/thunderstorms, return Tuesday and Tuesday
night with the approach and passage of a cold front. VFR returns
Wednesday under high pressure.

&&

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

&&

$$

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