101
FXUS61 KCTP 181131
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
731 AM EDT Sat May 18 2024

.SYNOPSIS...
The combination of a slow-moving and decaying frontal boundary
over Western Pennsylvania and an area of low pressure moving
across Southern Virginia will bring numerous showers to main
Central and Southern portions of Pennsylvania today.

Low pressure passing well to the south of Pennsylvania will
bring additional showers to primarily Central and Southern
portions of Pennsylvania through this afternoon.

High pressure will build into the region on Sunday accompanied
by generally rain-free conditions that are expected to persist
through the middle of next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A weak ridge of high pressure extending from the New England
states south along the Mid Atlantic Coast was helping to
maintain dry conditions across the eastern third of the state
early this morning, while several areas of showers were drifting
northeast across the Central and Western Mtns of the state.

Showers will spread into the region over, and to the east of
the Susq Valley as the morning progresses related to enhanced
UVVEL within the thermally indirect branch/beneath the left exit
region of a 110 kt upper level jet approaching from the south.

The associated periods of steadiest rain will last through the
late morning hours across the SE half of the CWA, while the
showers closer to the weakening front in the NW will be much
intermittent and widely scattered.

It appears that deep moisture up through the mid levels of the
atmosphere will persist for the bulk of the region today through
early tonight.

Additional rainfall of 3 or 4 tenths of an inch is likely across
the Scent Mtns and Lower Susq Valley while lighter amounts of
perhaps around another 0.10 of an inch will fall over the NW
Mtns.

High temps will be a notable amount below normal in the shallow
cold air damming regime across Central and Eastern PA with the
mercury reaching the low to mid 60s throughout the Central and
SE Valleys and upper 60s to mid 70s across the far NW zones.

Lows in the 55-60F range are +5-15F above mid May climo with
the larger departures across the western and northern
Alleghenies.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
Plenty of clouds will linger tonight and any breaks that develop
after midnight will likely lead to locally dense fog as sfc
dewpoints will stay moderately high and in the mid 50s in most
locations. Low temps will occupy a tight range between 52
(Northern and Western Mtns) and 58 deg F throughout the Lower
Susquehanna Valley and points just to the west.

Sunday is looking increasingly nice with high pressure
eventually allowing a good deal of sunshine throughout and
salvaging the second half of the weekend. Decreasing deep layer
moisture and a northerly wind component along with ridging at
the sfc and aloft should help highs recover nicely with temps
around 80F fcst in the NW Alleghenies and mid to upper 60s
elsewhere.

We are likely to see some areas of fog again Sunday night, and
temps will continue to trend warmer with dry weather persisting
into early next week with highs on Monday reaching the upper 70s
to mid 80s.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
A dry start to the extended period will be likely with high
pressure ridging building over the mid-atlantic region and a
deep surface low parked over the central plains. High pressure
and dry air will stay in place through Tuesday before the upper
level trough pushes them both out by Wednesday afternoon. 850mb
temps of near 16C along with surface warm air advection suggest
high temperatures could reach the mid 80s on Tuesday and
Wednesday.

By the middle of next week, upper troughing will move across
Pennsylvania and support a better chance for showers and
thunderstorms. At the surface, there remains plenty of model
uncertainty about the timing of a cold front. The mean timing is
Wednesday afternoon, but individual models bring precipitation
as early as Tuesday evening and as a late as Thursday morning.
If the front moves through Wednesday afternoon or evening, it
could produce the first threat for severe weather in some time
given the aforementioned WAA bringing greater instability.

After the front moves through, considerable uncertainty exists
in terms of how much and how frequent rain will be. A chance of
showers remains in place through the end of the week despite
zonal flow aloft providing little in the way of synoptic
forcing. The next chance for a widespread soaking rain will come
during the weekend with a center of low pressure developing
across the Ohio Valley by Friday afternoon.

&&

.AVIATION /11Z SATURDAY THROUGH WEDNESDAY/...
At 1120z, IFR persist over the northwestern highlands (BFD,
south to KFIG and KDUJ) overnight, with borderline IFR/MVFR
cigs expected over the central mtns (AOO, UNV). Interestingly,
JST and AOO are in what we see as brief period of VFR, thanks
to compensating subsidence, warming and drying within the left
rear quad of the 110 kt upper level jetlet. They should fall
back into MVFR to IFR later this morning and continue through
this afternoon. IPT has dropped to low- end MVFR cigs, while the
Lower Susq Valley remains low- end VFR (~4 kft cigs).

Conditions will deteriorate across the Lower Susq Valley this
morning as cigs continue to drop and an approx 3 hour period of
light to moderate rain moves in with 2-3 tenths additional QPF
expected. Look for fairly steady state conds elsewhere.

Patchy light rain will persist into the afternoon southeast of
the Allegheny Front, along with low-end MVFR cigs. For the
western highlands, cigs should improve to MVFR (perhaps even
low-end VFR) this afternoon although scattered rain showers are
possible.

Outlook...

Sun...Morning low cigs/fog possible. Becoming VFR by afternoon.

Mon...Patchy AM fog possible. Otherwise, becoming VFR.

Tue...Predominantly VFR, w/ no sig wx expected.

Wed...Sct to widespread SHRA/TSRA return.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SYNOPSIS...Lambert
NEAR TERM...Lambert
SHORT TERM...Lambert
LONG TERM...DeVoir/Bowen
AVIATION...Lambert/Evanego