PBZ issues Area Forecast Discussion (AFD) at Dec 8, 1:49 PM EST739
FXUS61 KPBZ 081849
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
149 PM EST Sun Dec 8 2024
.SYNOPSIS...
Rain returns late tonight and Monday with a warm front. Rain
will continue Tuesday with a crossing cold front, followed by
colder weather and a brief change to snow Wednesday.
&&
.NEAR TERM /THROUGH TONIGHT/...
KEY MESSAGES:
- Dry and mild through the remainder of the afternoon.
- Rain returns tonight with a passing warm front.
-------------------------------------------------------------
Winds have gradually subsided as expected this afternoon, with
only a few infrequent lingering gusts to 20-25 mph ongoing at
this time. Temperatures also continue to trend as forecast, with
mostly upper 40s and low 50s being observed across the lowlands
south of I-80, and mid 40s in the higher terrain and north of
I-80. Expect this mild and dry weather to continue through the
remainder of the day.
A shortwave trough currently located over the southern Plains
will trek northeastward over the Ohio Valley tonight into early
Monday morning. Cloud cover increases tonight as that system
approaches, with rain chances also increasing from southwest to
northeast mainly after midnight as a warm front pushes through.
With warm air advection in southerly flow and increasing cloud
cover helping to mitigate cooling, expect low temperatures
tonight to be on the milder side, running roughly 10 degrees
above normal lows this time of year. Latest ensemble guidance
suggests high confidence (>70% chance) in lows remaining above
freezing everywhere south of I-80, with medium confidence
(40-60% chance) in this occurring north of I-80.
&&
.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
KEY MESSAGES:
- Rain returns late tonight and Monday with a warm front
- Another round of rain Tuesday and Tuesday night with a cold
front
- Possible changeover to snow Tuesday night behind the front
-------------------------------------------------------------------
Rain continues Monday morning with the passing southern stream
shortwave. Ensemble guidance continues to indicate a greater
than 70% chance areawide for at least 0.5 inches of rainfall
before rain tapers off Monday afternoon as the shortwave departs
to the east. Locally heavier amounts may be observed along the
ridges east of Pittsburgh and Morgantown due to orographic
enhancement as a low-level jet ramps up Monday morning.
Ensembles suggest a 40-60% chance of greater than one inch of
rain in those areas. Lingering low level moisture could support
patchy light rain or drizzle Monday night (particularly along
the higher terrain), but with little or no additional rainfall
accumulation.
A digging shortwave trough over the Upper Midwest/Plains region
advances eastward on Tuesday. Surface low pressure is expected
to develop across the Tennessee Valley region and track across
Ohio into Western PA late Tuesday and Tuesday evening. A cold
front will cross the region as the low continues northeastward,
with another increase in rain expected. A strengthening jet
ahead of the upper trough should also enhance ascent across the
region as the low and cold front cross. Once again the heaviest
rainfall is expected to occur along the higher terrain where
ensembles indicate a 50-70% chance of at least 0.5 inches of
accumulation (in addition to the rainfall that occurs
tonight into Monday).
Cold advection behind the front will likely result in snow
mixing in with rain followed by a transition to all snow. Model
soundings and critical thicknesses suggest this changeover
occurs late Tuesday night or early Wednesday morning.
&&
.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
KEY MESSAGES:
- Much colder with snow chances mid to late work week.
- Seasonable temperatures and rain chances return over the
weekend.
-------------------------------------------------------------------
Model ensembles indicate the digging trough should cross the
Upper Ohio Valley region Wednesday, with rain transitioning to
snow as temperatures fall through the day under post-frontal
cold advection. A reinforcing trough is progged for a Thursday
passage, with snow showers possibly continuing during that time
mainly north of Pittsburgh. The reinforcing trough exits
Thursday night and dry weather returns under high pressure on
Friday.
Current probabilities for 2 inches or greater of snow are above
60 percent across the higher terrain areas, while remaining
less than 20 percent elsewhere. It appears the boundary layer
flow could remain too WSW for much lake effect in our area,
though uncertainty remains in the details this far out in the
forecast. Very cold temperatures are expected Wednesday and
Thursday nights under strong cold air advection. Latest guidance
suggests high chances (>80%) for lows dipping below 25F
Wednesday night, with areas outside of river valleys and metro
areas also seeing a >70% chance of dropping below 20F. Thursday
night trends even colder with 25th and 75th percentiles for low
temperatures ranging from single digits to mid teens,
respectively.
Warm advection ahead of the next shortwave trough tracking
eastward out of the Upper Midwest will return seasonable
temperatures and rain chances Saturday into Sunday.
&&
.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
VFR is prevailing at all area terminals. Winds have marginally
subsided from earlier today with many terminals gusting near 20kts.
VFR is expected to prevail through the evening hours before
degrading ahead of a warm front approaching the area from the SW.
ZZV is expected to be the first VFR domino to fall as rain
approaches the area. CIGs are expected to quickly drop to MVFR near
the onset of rain and then down to IFR as the column saturates. Most
area terminals are expected to be MVFR/IFR by 12z Monday. Low CIGs
will last through the TAF period at all terminals but steadier rain
is expected to taper near 18z.
Another 35-40kt low-level jet will nose its way into the region
after sunrise tomorrow and could bring some LLWS concerns back to
area terminals.
Outlook... Low level moisture should maintain restrictions and rain
chances continue Tuesday/Tuesday night with the approach and passage
of a cold front. Restrictions and rain/snow are expected Wednesday
under subsequent upper troughing and cold advection.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...Cermak
NEAR TERM...Cermak
SHORT TERM...Cermak/WM
LONG TERM...Cermak/WM
AVIATION...AK
Source:
PBZ issues Area Forecast Discussion (AFD) at Dec 8, 1:49 PM EST---------------
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