-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KCTP 172043
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
443 PM EDT Wed Apr 17 2024

.SYNOPSIS...
-Marginal severe t-storm risk late this afternoon into the
 early evening primarily west of the Allegheny Plateau
-Unsettled with periods of showers through Friday
-Weekend cool down; monitoring frost/freeze risk Saturday-Monday

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Warm front lifting through central PA this afternoon. Best
convergence and forcing for showers has exited east and north,
but with increasing warmth and moisture lifting over the
Alleghenies, starting to see mixed layer CAPES on the rise along
and west of the Alleghenies. CAMs differ on degree of
stratification along and east of the mountains, with most
putting a damper on deep convection as it arrives from the Ohio
Valley along occlusion by mid evening. With sufficient shear to
organize storms as they exit OH and move through western PA,
we`ll be watching upstream activity progress as weakening
occurs after sunset.

A MRGL outlook remains in effect from SPC into this evening for
western and central parts of Central PA for this possibility.
And a few heavy downpours can accompany some of the storms as PW
near 1.25" supports higher rates. Progressive storm motion
keeps this risk low at the moment. With clouds and
precipitation, it will be mild tonight with lows in the 45-55F
range. Some fog and drizzle is likely late tonight into early
Thursday morning across east- central PA.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
Improving conditions on the way for Thu thanks to rising
heights as the remnants of the upper low pass well north of PA
and deep layer moisture exit to the east. Residual low level
moisture combined with upslope flow should support lingering
drizzle over the northern mountains Thu morning, Occluded front
pushes into central PA with a drier westerly flow arriving
behind it to produce at least partial clearing. Atmosphere
appears capped for afternoon showers however.

Most model guidance indicates a closed upper low will pass north
of the region Friday, with a trailing occluded front coming
through Central PA Friday afternoon/evening. The triple point
low is progged to pass south of the forecast area, so the severe
weather threat looks very low. A decent plume of moisture with
pwats close to +2SD should support POPs close to 100pct and some
heavier showers. However, the best large scale forcing as
inferred by model 300-500mb qvec convergence fields passes well
north of PA, so expect overall rainfall to be less than
impressive. Latest plumes support amounts between 0.1 and 0.2
inches in general.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
The bulk of model guidance suggests dry conditions prevailing by
Saturday evening expected to continue into Tuesday morning as
high pressure build into the area. Upper-level troughing does
support below-average temperatures for the majority of the
period.

The combination of light winds, dry air, and mostly clear skies
associated with the surface ridge is likely to result in areas
of frost throughout the weekend. The greatest risk of frost
throughout the timeframe will be stationed over the northern
mountains where the growing season is not active, but areas in
the growing season further south could also be affected Sunday
night into Monday morning.

Temperatures are expected to moderate by Tuesday with the
surface high pressure shifting eastward off the east coast and
an approaching shortwave brings the next chance of showers. The
best chance for precipitation will come later on Tuesday,
although cannot rule out precipitation starting across western
PA during the morning hours.

&&

.AVIATION /21Z WEDNESDAY THROUGH MONDAY/...
-- Changed Discussion --
Late afternoon update.

Most of the warm advection showers off to the northeast now.
Dry slot with BINOVC now across much of the area. This has
resulted in some heating and temperatures up some. However,
looking just a few showers into central areas, with a weakening
trend.

Across the far west, the airmass is much warmer, but nothing
much near BFD or JST at this point. May add thunder to these
2 sites later, if something forms to the west and heads toward
these sites.

Thus for now, did back off on lower conditions and showers early
on.

Earlier discussion below.

Scattered showers will continue across central PA for the next
couple of hours (with highest chances lowering after the 21-22Z
Wednesday timeframe). At this time AOO seems like the airfield
most likely to stay dry, with UNV breaking into a slight dry
slot in precipitation after this initial line of showers makes
it through the terminal. VFR conds are generally expected with
higher-level cloud bases although some drops towards 4-6SM in
SHRA cannot be ruled out. Have opted to keep any drops in vsby
during the near-term (18Z-22Z) due to low (> 20%) confidence on
sub-VFR vsbys.

The next batch of rain (currently stationed over OH) will make
way into the area later this evening into the early morning
hours of Thursday. Some TSRA cannot be ruled out across the
western airfields (BFD/JST/AOO, lesser UNV) but confidence
remains low (10-20%) on this complex remaining robust enough to
continue TSRA as it approaches these locations. Thus, have opted
to keep VCTS out of this TAF package, but will deserve continued
analysis in next TAF issuances.

Southeasterly flow this evening, coupled with lower cigs with
associated rain, will support lower cigs overnight. Recent HREF
guidance highlights IPT/LNS as the two airfields with highest
probabilities of IFR cigs (70+%), with guidance backing off
slightly at MDT. Further to the east, slightly less confidence
(< 30%) on IFR cigs, but MVFR cigs seem likely with higher
(60-70%) confidence in the overnight period. MVFR cigs are
expected to continue through 18Z Thursday at all airfields
except at AOO at this time.

Outlook...

Fri...CFROPA. Ocnl dips to IFR.

Sat...Light SHRA N, no sig wx elsewhere.

Sun-Mon...No sig wx.
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...Steinbugl
NEAR TERM...Steinbugl
SHORT TERM...DeVoir/Fitzgerald/Steinbugl
LONG TERM...Lambert/Fitzgerald/NPB
AVIATION...Martin/NPB