PBZ issues Area Forecast Discussion (AFD) at Feb 27, 6:39 PM EST049
FXUS61 KPBZ 272339
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
639 PM EST Thu Feb 27 2025
.SYNOPSIS...
Additional showers expected this evening with the passage of an
upper level wave. Rain will change to snow late tonight as
colder air spreads across the region. Below normal temperatures for
the weekend will be followed up by well above normal values by
the middle of next week.
&&
.NEAR TERM /THROUGH FRIDAY/...
KEY MESSAGES:
- Rain/snow chances return tonight with some accumulation possible
in WV ridges.
- Marginal Risk (1/5) for localized instances of gusty wind and
small hail in eastern Ohio.
-------------------------------------------------------------------
Continuing cold advection in west/northwest flow has maintained
a blanket of stratus through the daytime hours today, though
some breaks in the coverage and a transition to a more cumulus
nature is now working into eastern Ohio as the magnitude of the
advection lessens. Lapse rates have steepened with the erosion
of the warm nose but moisture has shallowed with recent ACARS
soundings showing a cut off above ~800 mb, so only some very
light showers are being observed. With the steeper lapse rates,
25-30 mph gusts will continue this afternoon with mixing into a
30-35 kt low level jet.
A reinforcing cold front and mid-level shortwave will approach
later this evening and spark off additional scattered rain
showers. Within these, there is a conditional, low confidence
potential for gusty wind and small hail in the most potent
updrafts in eastern Ohio. SPC has placed that part of the region
in a Marginal Risk (1/5) for severe weather today. The main
limiting factors will be the amount of instability present and
the equilibrium heights and whether or not they're high enough
to really tap into the elevated wind field aloft. Along with
that, HREF MUCAPE maxes out below 500 J/kg, and hi res
soundings suggest it'll be a skinny CAPE profile. We likely
won't be relying on DCAPE with not much dry air to work with,
and RAP projections max out those values at <200 J/kg, so
overall this looks to be a localized threat conditional on
maximizing the environment.
Cold air will be lagging behind the initial development of rain
showers, but it will eventually catch up and allow some wet
snowflakes to mix in, especially in the most potent updrafts.
We'll then see a transition to a period of all snow showers in
the early overnight hours, but the longevity should be cut off
by shallowing moisture depth. Poor SLRs and warm surface
temperatures will limit any accumulation potential save perhaps
some elevated surfaces that could see a slushy dusting. Where
it is likely to linger the longest is in the WV ridges,
specifically eastern Tucker County, and locally colder
temperatures could allow for some wet snow accumulation on the
order of 1-3 inches. Probability for exceeding 3 inches is low,
and especially given the still warmer ground temperatures and
inefficient rates/SLRs, not very confident that accumulation
will be notable even there.
&&
.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
KEY MESSAGES:
- Dry Friday daytime hours with increasing evening precip chances.
- Lingering snow showers on Saturday with colder temperatures.
--------------------------------------------------------------------
Aside from perhaps some lingering upslope snow showers early Friday
morning, dry weather returns in the wake of the departing trough as
a brief bout of surface high pressure noses in and flat ridging
establishes in the mid-levels. Cloud coverage will try to retreat to
the north with HREF soundings suggesting drier mid-levels south of
Pittsburgh. 25th/75th coverage spread is nearly bimodal in that area
with either mostly clear skies or overcast skies, so while the
deterministic forecast represents the mean, a cloudy solution could
mute highs to the upper 40s and a clearer solution to the mid 50s.
Farther north, even the low end of the goal posts maintains cloudy
skies lending higher confidence, so if highs were to err one way or
another, it's most likely to the south. Mixing and a tightening
gradient will promote gusty wind Friday and Saturday with
probability for >30 mph exceeding 70% both days. There's also
elevated probability for advisory level gusts in Eastern Tucker
County, so headlines may be needed down there in the next 24
hours.
An Alberta Clipper-esque system quickly slides by Friday evening
with a leading shortwave accompanying another longwave trough. The
warm frontal precipitation is likely to hold off to our north with
the cold front and a pre-frontal trough bringing the precip axis
down overnight. Most likely timing is around 8pm for NW PA and
midnight for Pittsburgh, though some uncertainty lingers in either
direction. Precip will come in the form of rain for most Friday
night, though a later arrival up north could allow some wet snow to
mix in with little accumulation concern. The passage of the cold
front will usher in low-level cold advection on Saturday with
temperatures dropping through the day, and lingering vorticity
advection will support low-level cloud coverage and light snow
showers through Saturday evening.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
KEY MESSAGES:
- Dry weather returns Sunday with next rain chances late Tuesday.
- Temperatures moderate into mid-week.
-------------------------------------------------------------------
High pressure builds in quickly on Sunday with high confidence
returning dry weather and a colder air mass. Slight deviation from
the ensemble mean in the depth of the departing trough may impact
how quickly cloud coverage retreats and hold highs a touch colder
than forecast north of Pittsburgh. The gradient will lessen through
the day suggesting that wind gusts will diminish, and likewise NBM
probs for gusts >30 mph drop to 20% or less outside of the ridges.
Confidence remains high in dry weather headed into the beginning of
next week with little clustered ensemble deviation locally. Surface
high pressure establishes overhead on Monday as mid-level ridging
amplifies and migrates east out of the midwest in response to a
digging WCONUS trough. With southerly flow establishing on the
western side of the high Monday and Tuesday, warm advection should
pump high temperatures back to near-normal on Monday and well-above
normal Tuesday and Wednesday. Given a cold NBM bias as we approach
the exit of the winter season, it may be underdoing highs by a
bit, but an increase in cloud coverage beginning on Tuesday and
ramping up precip chances Tuesday night into Wednesday does lend
some question as to if we'll be able to capitalize on the
warmth anyway; early NBM suggestions are that 30-50% probs for
60F reach the Mason Dixon line on Tuesday and we see 50-80%
probs overspread a good portion of the area south of I-80 on
Wednesday.
An ejecting trough and passing low pressure will be responsible for
said rain chances. With discrepancy on the upper level pattern, will
have to wait for more details, but the QPF goal posts sit between
roughly a quarter inch and one inch.
&&
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
A round of showers and a few low-topped thunderstorms is moving
through the region this evening ahead of the cold front. Chances
for lightning remains highest across eastern Ohio, but continues
to wane with fading light. Probabilities are lower (roughly
20-40%) farther east towards PIT and MGW, where PROB30s for TSRA
were favored over prevailing mention of thunder to reflect this
greater uncertainty.
In the wake of the front, northwest winds filter colder air into
the area and rain showers transition to snow, though little
accumulation is expected as temperatures remain marginal,
hovering around or just above freezing for most of the night.
Meanwhile, MVFR/IFR restrictions continue in the wake of the
front before improving to VFR mid to late Friday morning. Winds
briefly relax during pre-dawn hours Friday as they back to
southwesterly, then increase once again by mid to late morning
to 10-50 knots with gusts to 20-25 knots. Gusty winds will be
maintained into Friday night.
Outlook...
VFR briefly returns during the day Friday under building high
pressure and breezy southwest winds. Restrictions and rain
potential return late Friday night with another cold front.
Breezy northwest winds and snow showers (and associated
restrictions) are then expected Saturday in the wake of Friday
night's cold front and as another upper shortwave trough passes
over the area. High pressure brings a return of VFR Sunday and
Monday.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...MLB
NEAR TERM...MLB
SHORT TERM...MLB
LONG TERM...MLB
AVIATION...Cermak/Rackley
Source:
PBZ issues Area Forecast Discussion (AFD) at Feb 27, 6:39 PM EST---------------
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