276
FXUS61 KCTP 171115
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
715 AM EDT Fri May 17 2024

.SYNOPSIS...
A weakening cold front approaching from the Ohio Valley today
and low pressure passing well to the south of us on Saturday
will team up to bring us occasional showers later today through
Saturday morning.

A ridge of high pressure will build into the Commonwealth for
Sunday through early next week, bringing warmer and drier
conditions, followed by a return of showers and scattered
thunderstorms for the middle of the week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A weak and nearly stationary north/south sfc trough extended
from near KELZ to KUNV and KCBE early today and separated
widespread stratocu clouds to the east from notably
higher/thinner clouds to the west.

early morning temperatures were highly uniform across the region
and mainly between 55 and 60F.

Clouds may be thin enough across the Susq Valley and points east
for some breaks of sunshine during the 12-16Z period, before
thickening layered clouds aloft spread in from the west this
afternoon and evening.

Nearly calm air with moderate dewpoints in the low to mid 50s
will help to create some patchy valley fog across the south
Central Mountains and into the Susquehanna`s West Branch Valleys
through 13Z today.

HREF and its high res members suggest that the onset of rain
will likely (60-70 percent confidence) be late this Friday
morning across the Western Mountains of the state, but
should hold off until the mid to late afternoon hours across
the Central Mountains and possibly won`t begin until early this
evening over the Susquehanna Valley and points east.

MU CAPE will be very limited today and generally below 500 J?KG
across our far western zones and non-existent across the far
east. Thus, previous thinking and our current inclusion of a
SCHC for embedded TSRA with the showers across the Central Mtns
late today and this evening may be overdone.

Highs today will be around 70F across the Western Mtns and in
the low to mid 70s across the Central Mtns and Susq Valley.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/...
The axis of showers will continue to propagate slowly eastward
tonight within an area of relatively high PWs of 1.2-1.5"and
marginally unstable airmass (though again, the bulk of the
instability will stay west of the Allegheny Plateau).

Scattered to numerous showers will continue into Saturday as
southeasterly flow helps keep overcast skies and cooler
conditions in place.

It will be cloudy, dreary and somewhat chilly Saturday, but the
majority of the rain will occur in the morning in most places.

HREF 48 hour Prob Matched Mean precip ranges from around 1
inch across the Western Mtns (with some higher point amounts) to
as little as a tenth or so across the far east. WPCs MRGL Risk
for excessive rainfall nips Somerset County for tonight and
Saturday, but we don`t foresee even high end amounts of 1.5
inches causing any significant problems with flooding on even the
smallest streams. Would need to see over 2.5 inches for any
flooding issues to develop across the West.

Temperatures on Saturday will top out in the 60s, though a
classic cold air damming scenario could keep highs in the upper
50s in a few locations.

Improving conditions are likely on Sunday as an area of high
pressure over the northeast sags southward. This will promote
some breaks in the clouds and a bit milder temperatures. Some
uncertainty remains in how stubborn the clouds will be on
Sunday, but Sunday looks much better than Saturday for outdoor
plans and activities.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
*Drying trend with more sun and warmer temperatures Mon-Tue.

Decent model and ensemble signal for dry weather and more
sunshine leading to a seasonal warming trend next Monday-
Wednesday as a potential cutoff low parks over the western
Atlantic and high pressure builds overhead. Max temps are
forecast to climb back into the 75-85F range through 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.

After the front moves through, considerable uncertainty exists
in terms of how much and how frequent rain will be. Have kept a
chance of showers in place through the end of the week. Fairly
high confidence in temperatures being close to average in zonal
flow.

&&

.AVIATION /11Z FRIDAY THROUGH TUESDAY/...
As the sun came up this morning, low clouds (IFR over the
western highlands and generally MVFR elsewhere) were observed
across central PA. At the same time, high clouds are streaming
in from the Ohio Valley and overtopping the lower cloud deck.

Ceiling bases with the low cloud deck should gradually begin to
lift after sunrise. However, an approaching warm front will
spread showers (and perhaps some thunder) and lowering cigs into
the western half of PA during the afternoon and evening hours.
Latest ensemble prob charts indicate an increasing probability
of IFR cigs (50-70% chc) by late evening over the western
highlands (JST, BFD).

IFR conds will continue into the overnight across the western
highlands, with cigs expected to drop to borderline IFR/MVFR
late this evening into the overnight across the central mtns.
The Susq Valley should see cigs drop to MVFR overnight. Periods
of rain will continue into the overnight hours as well.

Outlook...

Sat...Restrictive lower ceilings and periods of rain
continuing.

Sun...Morning low cigs/fog possible.

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

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

&&

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

&&

$$

SYNOPSIS...Lambert/Steinbugl
NEAR TERM...Lambert/Banghoff
SHORT TERM...Lambert/Steinbugl/Banghoff
LONG TERM...Guseman/Banghoff
AVIATION...Evanego