PBZ issues Area Forecast Discussion (AFD) at Jul 21, 12:26 PM EDT221
FXUS61 KPBZ 211626
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
1226 PM EDT Mon Jul 21 2025
.SYNOPSIS...
Pleasant weather early this week with seasonable temperatures,
no rain, and low humidity. Heat, humidity, and storm chances
return late week.
&&
.NEAR TERM /THROUGH TUESDAY/...
KEY MESSAGES:
- Lowering humidity today; pleasant, dry weather with seasonable
temperatures through Tuesday.
---------------------------------------------------------------
The WPC 12Z surface analysis shows a cold front has drifted
south of the area, into central West Virginia. In its wake, much
drier air is expected to fill in. The 12Z sounding already shows
a shallow near-suaface moist layer topped by a stark subsidence
inversion. This has led to a shallow cu deck with mixing, which
is expected to decrease in coverage through the day, as more dry
air aloft is mixed to the surface. This will spell lowering
humidity and post-frontal seasonable temperatures. Tonight,
these calm, clear conditions will lead to efficient radiative
cooling and, potentially, the coolest night since June 11th.
Stream fog is possible on the competitively warm area rivers.
Tomorrow will spell more of the same with some indication of an
even drier airmass aloft as the surface high drifts southeast
and subsidence continues. Clear skies are most likely, with dry
conditions and more seasonable temperatures.
&&
.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
KEY MESSAGES:
- Warming trend through Thursday with upper ridging.
----------------------------------------------------------------
Stark mid-to-upper level ridging is expected from Tuesday
through Thursday that will result in a rapid warmup. 500mb
heights will push from roughly 588dm to 594dm, placing the area
squarely on the northern periphery of the heat dome by
Thursday. Humidity will slightly lag with dry antecedent
conditions before the ridging, and moisture advection needed to
saturate low levels. Because of this, heat indices will be
close to temperatures Wednesday (upper 80s to low 90s). This
will also largely suppress rain chances, and result in mostly
clear skies. 850mb moisture transport will take largely until
Thursday to truly ramp up.
This ridging and moisture advection may take highs into the 90s
for most, with heat indices (95F to 100F) approaching advisory
criteria (100F to 105F) for much of the lowlands. In addition,
low moisture will allow some SBCAPE to develop, as indicated
with a noted rise of >100 SBCAPE from 25% to Wednesday to 85% on
Thursday. This may allow for possible rain chances, though not
noted in the forecast yet. With LREF mean DCAPE near 1000 J/kg,
a downburst threat is possible, in the low probability event
that a storm is able to materialize.
&&
.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
KEY MESSAGES:
- Shower/thunderstorm chances increase Friday and into weekend.
- Large uncertainty in the pattern mid-to-late next week.
-------------------------------------------------------------------
All four WPC clusters indicate some breakdown of the 594dm
ridge from Thursday into Friday, with heights potentially
falling further into Saturday as the ridge axis retrogrades and
reestablish in the central CONUS with high confidence. This
will put the area on the northern periphery of a decaying ridge
Friday into Saturday, and on the northeast side of a
reestablishing ridge early next week. Climatologically, this
would hint at increasing chances of MCS development and passages
across the northeast, with embedded severe threats. Both CSU ML
and CIPS support this with increasing severe chances into
Friday and Saturday. With PWATs nearer the 90th percentile yet
again with encroaching moisture and increasing chances of
storms, WPC has introduced a Day-5 marginal chance of excessive
rainfall.
A ridge breakdown would allude to decreasing temperature trends
into the weekend and early next week. A majority of ensembles
agree, through uncertainty maximizes on Saturday with
uncertainties in convection in cloud cover. 80% of ensembles
have the area below heat advisory criteria Saturday and beyond,
compared to the 40% on Friday.
The position and amplitude of the central CONUS heat dome will
influence temperatures by middle-to-late next week. Spread is
very wide. A lower amplitude ridge would leave temperatures in
the middle of the road. A high amplitude ridge down the spine
of the Rockies would keep the area seasonably cool and dry, and
a high amplitude ridge over the Mississippi Valley would tend
toward a warmer and more active pattern.
&&
.AVIATION /16Z MONDAY THROUGH FRIDAY/...
High pressure and dry advection will secure VFR areawide today
with mostly scattered diurnal cu. Post-frontal mixing may result
in occasional NW wind gusts between 15-20kts from 15z-00z before
subsiding after sunset.
Outlook...
High confidence in VFR and dry weather through Thursday under
the influence of high pressure. Strong radiational cooling
Tuesday/Wednesday mornings may be enough to foster localized
river valley fog that impacts typical river valley terminals.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...Milcarek
NEAR TERM...Milcarek
SHORT TERM...Milcarek
LONG TERM...Milcarek
AVIATION...Cermak/Frazier
Source:
PBZ issues Area Forecast Discussion (AFD) at Jul 21, 12:26 PM EDT---------------
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