303
FXUS61 KCTP 182239
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
639 PM EDT Sat May 18 2024

.SYNOPSIS...
An upper trough overhead will slide east through the evening
with showers decreasing by late tonight. High pressure will
start to build into the region on Sunday accompanied by
generally rain- free conditions that are expected to persist
through the middle of next week. A storm system should arrive
Wed, and perhaps generate severe weather and heavy rain.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Scattered open cellular showers continue to roam areas from the
Finglerlakes to the WC Mountains early this evening as upper low
tracks off the coast and drier air slowly works in aloft behind
it. Beyond some brief slow moving downpours, these present
little concern given weak shear and marginal bouyancy. Lighter
showers over my far southeastern counties are slowly dissipating
and moving east as well, so it`s fair to say that slow
improvement is in progress across the area.

Showers will taper by late evening, and as the sky begins to
clear under the influence of NVA/rising heights, fog will form
esp where it rained this aftn and eve and some could become
locally dense in the predawn hours. Lows will range from the mid
50s to around 60.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
High pressure rolls in for Sunday. Clouds/fog in the AM clear
out nicely. However, just enough instability develops and enough
moisture lingers to pop a couple of SHRA. Literally just a few
with the highest probability (30pct) over the SErn hill tops.
Maxes in the 70s will be pretty normal. We are likely to see
some areas of fog again Sunday night with the sky clearing out
better, but dewpoints not dipping out of the m50s.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
No real changes or updates from the previous long term
discussion. Monday and Tuesday will be dominated by high
pressure ridging and dry conditions before the next system makes
its way into the region by Wednesday for the return of the
unsettled pattern.

Previous discussion...
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 /00Z SUNDAY THROUGH THURSDAY/...
21Z Update...Recent HREF/LAMP guidance has suggested airfields
across SE PA (MDT/LNS) going towards low-end MVFR to high-end
IFR CIGs overnight compared to previous guidance. Recent RAP
soundings also outline this potential (mainly after 03Z Sunday,
where winds could become calm) with increased low-level
moisture. Have introduced lower cloud decks in the 03Z-12Z
Sunday timeframe given multiple runs of GFS LAMP guidance and
recent HREF guidance trending downwards, although there is low-
to-moderate (30-40%) confidence at this time.

Prev...
Lots of SHRA popped over the Alleghenies, and are
moving only slowly. MVFR cigs in the SErn half of the area will
linger into the night but probably break up some more. Rain
showers should mostly be over by the early evening hours as the
upper level trough drifts east. Remaining low level moisture and
night time cooling will make for fog development for Sunday
morning likely. Most sites will likely drop to IFR for a time as
low clouds and fog take hold of the region through the early
morning hours Sunday.

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.

Thu...Chc of TSRA.

&&

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

&&

$$

SYNOPSIS...Lambert/DeVoir
NEAR TERM...DeVoir/Dangelo
SHORT TERM...Dangelo
LONG TERM...Bowen
AVIATION...NPB/Bowen