PBZ issues Area Forecast Discussion (AFD) at May 23, 8:51 AM EDT046
FXUS61 KPBZ 231251
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
851 AM EDT Fri May 23 2025
.SYNOPSIS...
An upper low will linger, ushering in cooler northwest flow with some
shower chances today, becoming more localized by Saturday. A more
seasonable and dry Memorial Day is forecast, with rain chances
increasing Tuesday.
&&
.NEAR TERM /THROUGH TONIGHT/...
KEY MESSAGES:
- Continued shower chances today, decreasing in coverage overnight.
- Temperatures remain seasonably cool.
-------------------------------------------------------------------
An elongated upper low will continue to sit over the northeast for
the beginning of the period, consolidating over the Saint Lawrence
River Valley by tonight. This will continue to usher in cool,
northwest flow in the low-levels, keeping surface temperature
10 to 15 degrees below average during the day. In turn, cool air
will continue to allow destabilized or marginally stable low-
level profiles, that will continue shower chances.
Chances are the highest downstream of the Erie lake fetch,
where additional moisture is available and low-level cold
advection will be maximized, as well as in the PA ridges where
upslope northwesterly flow aids in weak lift. For our area,
this lends to higher chances north and east of Pittsburgh, and
lower chances southwest today. There is some idea that coverage
maximizes late this morning through this afternoon with diurnal
heating and destabilization combined with an weak upper
shortwave passage. After the loss of heating, chances decrease
from southwest to northeast, confined to forcing and lake
moisture, with some clearing possible southwest of Pittsburgh as
drier-low level air makes its way in tonight.
In areas that do clear, patchy fog, in valleys remains possible
late. Radiative cooling maintains a 60% to 90% of lows <40F
southwest of the city, but just a 10% to 20% chance of lows
below freezing. Chances of 36F maximize at just 40%, precluding
frost headlines tonight for now, though isolated drainage basins
may experience some in any clearing.
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
KEY MESSAGES:
- Lingering showers north Saturday, otherwise dry and cool.
- Slightly warmer and dry Sunday.
----------------------------------------------------------------
Much like a typical winter regime, showers may tend to hang
around a bit longer for the I-80 corridor and higher elevations
Saturday with lake and orographic influence, as the upper low
draws away. This remains a fairly high confidence period with
little variation the 500mb clustered height field. As drier air
moves in Saturday, and mixing ensues, cloud coverage is expected
to decrease throughout the day northwest of Pittsburgh, along with
shower chances. Highs remain around 10 to 15 degree below
average with continued cold air aloft.
There is high confidence in at least a brief bout or ridging
Sunday as the 500mb low makes its way into the Canadian
Maritimes, though there is a slight difference between the 1)
Euro dominated cluster (showing ridging), vs. 2) GEFS dominated
cluster (showing a low- amplitude shortwave late Sunday). This
may mean the difference between 1) continued dry and slightly
warmer weather vs. 2) continued cool highs with some slight
shower chances in the I-80 corridor and ridges. Regardless of
the outcome, there is high confidence temperatures remain
seasonably cool.
&&
.LONG TERM /MONDAY THROUGH THURSDAY/...
KEY MESSAGES:
- Uncertainty increases in the pattern next week.
- Moderating temperatures, but still slightly below normal is most
favored.
-------------------------------------------------------------------
Confidence has increased in a pleasant Memorial day, with highs
closer to seasonal normals and precipitation chances >10%. The day
may start clearer, with clouds increasing overnight ahead of the next
weather system.
Clustered 500mb variance increases Monday into Tuesday with
uncertainty as to weather another upstream trough pivots into
northern Canada or not. The wettest of all scenarios into Tuesday,
with a 50% to 70% chance of >1" has a deeper trough or upper low
development in the upper Midwest to south-central Canada, pulling the
storm track more northwest. Direr scenarios result from either
continued ridging (which would also keep us warmer) or the
development of a trough over us, pushing the storm track farther
south and keeping us cool. Regardless of the outcome, there is at
least a 60% (I-80 and north) to 90% (WV mountains) chance of seeing
some rain Tuesday.
Late week will very much depend on the development (or lack thereof)
of the aforementioned eastern tough. Clusters have scenarios from:
the trough on or past us (generally cooler and wetter), to the trough
weaker and west of us (warmer and wetter), to the trough well into
the Canadian Maritimes (drier and warmer). So anything is still on
the table. Late week highs could be anywhere from the upper 60s to
low 80s.
&&
.AVIATION /13Z FRIDAY THROUGH TUESDAY/...
West to northwest flow continues as low pressure tracks from
southern to northern New England over the next 24 hours. While
significant drying is in progress above 10,000 feet, the low
levels should remain more saturated with areas north of I-70
seeing a mix of MVFR and IFR ceilings and scattered light showers
to start the period. Improvement is expected throughout the day
with VFR returning to most if not all terminals by afternoon,
though increased mixing will also result in an uptick in
northwest winds with gusts to 20 knots possible late morning
through the afternoon.
There will be less rain around today than the past couple of
days, but isolated to widely-scattered showers linger into
Saturday morning primarily along and north of a BVI-PIT-LBE
line. Southern airports like ZZV and MGW are more likely to
scatter out today and Saturday with central and northern areas
keeping mainly VFR ceilings, although MVFR may return at FKL and
DUJ Saturday morning.
Outlook...
Sunday through Tuesday will likely remain free of ceiling or
visibility restrictions. Low pressure tracking up the Ohio
Valley eventually brings rain chances and restrictions back to
the area Tuesday night.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...Milcarek
NEAR TERM...MLB/Milcarek
SHORT TERM...Milcarek
LONG TERM...Milcarek
AVIATION...Cermak/Craven
Source:
PBZ issues Area Forecast Discussion (AFD) at May 23, 8:51 AM EDT---------------
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