PBZ issues Area Forecast Discussion (AFD) at Dec 26, 2:56 AM EST243
FXUS61 KPBZ 260756
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
256 AM EST Thu Dec 26 2024
.SYNOPSIS...
Dry weather is expected through Friday afternoon with
temperature rising around 10 degrees above the daily average. A
series of low pressure systems will promote widespread Friday
night through Monday while temperature remains above normal.
&&
.NEAR TERM /THROUGH TONIGHT/...
KEY MESSAGES:
- Probabilities favor some amount of sunshine Thursday
afternoon, with longer duration of sunshine to the southeast.
- Expect high temperature around 5-10 degrees above the daily
average.
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Weak height rises as an embedded shortwave over Ohio lifts
northward will allow subsidence to slowly erode area clouds
through the day Thursday. By 3pm, ensembles suggest high
probabilities (60-80%) for enough cloud breaks to enjoy some sun
before it sets, with highest confidence around/east of
Pittsburgh. Enjoy it before another multi-day run of cloudiness
develops! Modest warm advection and some insolation will
continue the prior temperature rises to aid highs reaching 5-10
degrees above the daily average.
Above normal low temperature is favored Thursday night as warm
advection aloft increases mid-high level cloud decks ahead of
the first in a series of lows lifting NE out of the southern
Great Plains.
&&
.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
KEY MESSAGES:
- Back to back low pressure systems will generate widespread
rain, with higher QPF amounts likely with second system.
- Associated warm air will drive temperature 15 to 20 degrees
above the daily average.
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Southerly flow is expected to increase through the day Friday as
low pressure beings to lift out of Texarkana toward the western
Great Lakes. Influence from surface high pressure over New
England and subsidence ahead of the upper shortwave favors dry
weather holding out for most of the daylight hours. The main
influence will be increased cloud cover at temperature rising 10
to 15 degrees above the daily average.
Rain is favored to overspread the region Friday night into
Saturday morning as the upper shortwave lifts NW of the region.
Upper jet positioning and terrain convergence will favor a
corridor of higher QPF to the south and east of Pittsburgh,
where probabilities of >0.25" are generally above 60%
(probabilities fall to the NW). Overnight temperatures are
likely to fall most notably after precipitation onset due to
wet-bulbing before steadying as those effects are countered by
warm advection. Ensembles favor a downward trend in
precipitation chances Saturday amid weak shortwave ridging
between systems, with the occasional light rain/sprinkle
occurring as a result of warm, moist air being in place. Models
suggest that locations along and south of I-70 will have a
40-70% probability of 60+ degree highs for Saturday afternoon.
The next low pressure system and upper trough will quickly
follow late Saturday through Sunday, taking more of an eastward
jaunt as its lifts northward than the first system. Confidence
is high for another round of widespread rain that likely will
have a better Gulf of Mexico moisture fetch leading to higher
QPF totals. Uncertainty increases in the timing and depth of the
lifting trough feature, which will likely impact the positioning
and high-end potential of the QPF axis. Mean 24-hour totals at
this time suggest an additional 0.75"-1.5" of rain on top of
Saturday morning's total, but large model QPF spread highlights
that uncertainty in the system positioning/dynamics. AT this
time, flooding isn't a concern though higher-end totals may
cause some river locations (most likely along the Monongahela
River) to reach action stages. Sunday night likely features a
transitional period is the system begins to move northeast, with
dry advection behind the surface cold front eroding at
precipitation chances and offer some temperature reduction.
&&
.LONG TERM /MONDAY THROUGH WEDNESDAY/...
KEY MESSAGES:
- Temperatures well above-average for the weekend.
- Rain returns Saturday and lingers into the start of next week.
--------------------------------------------------------------------
Early model consensus favors dwindling of precipitation chances
Monday in the wake of Sunday's system, with weak vorticity
advection in NW flow. However, if that system more quickly
transits to the NE and allows for zonal flow to develop, current
precipitation chances may end up overstate. This will also
dictate the degree of cooling seen Monday, though confidence is
very high that temperature will remain at least 5-10 degrees
above normal.
Ensembles currently favor another upper level trough passage
around Tuesday that may presage a pattern shift (longwave
eastern CONUS trough) ahead of the New Year. This scenario will
result in periodic precipitation chances that lends to more
lake-favored areas (northwest PA and the higher terrain) and
temperature dropping below the daily averages. A lower
probability scenario does exist where Caribbean ridging remains
more stubborn and limits height falls over the Upper Ohio River
Valley; this would likely delay temperature falls and keep more
widespread precipitation chances in play.
&&
.AVIATION /07Z THURSDAY THROUGH MONDAY/...
Guidance indicates improvement to VFR is likely overnight as the
stratocu deck erodes northward. Will likely see MVFR fog develop
at the fog prone ports as moisture near the surface remains
elevated. The low clouds will continue to decay northward and
FKL and DUJ should see these clouds scattering out by late
afternoon or early evening.
Outlook...
VFR is expected through Friday under high pressure.
Restrictions and rain are likely Friday night and Saturday with
a crossing warm front. More widespread restrictions and rain are
expected again Saturday night through Monday with low pressure.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...Frazier
NEAR TERM...Frazier
SHORT TERM...Frazier
LONG TERM...Frazier
AVIATION...WM
Source:
PBZ issues Area Forecast Discussion (AFD) at Dec 26, 2:56 AM EST---------------
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