696
FXUS61 KCTP 171755
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
155 PM EDT Fri May 17 2024

.SYNOPSIS...
*Showers spread west to east this afternoon through tonight
*Weekend starts wet but ends dry in most areas (Saturdayradar mosaic shows showers slowly advancing into
western parts of CPA. Latest hires models depict slow moving
rain showers spreading into the central mtns by mid to late
afternoon before reaching the Susquehanna River Valley late
tonight into early Saturday morning.

WPC issued MPD#283 highlighting potential for some of the slow
moving showers to produce locally heavy downpours across the
south central Alleghenies particularly Somerset and Bedford
Counties. The 12Z HREF PMM along with the latest HRRR suggest
the greatest risk of heavy rain is to the south of our area
focused more in the MD/WV panhandles into the Blue
Ridge/northern VA.

Previous Discussion Issued: 1158 AM EDT Fri May 17 2024

Geocolor visible satellite shows multi-layer cloud decks across
CPA with lower stratus/stratocu drifting to the ENE beneath mid
and high level clouds streaming in from the southwest. Despite
some peaks of sun earlier this morning, expect cloudy skies for
the rest of the day with highs within a few degrees of mid May
climo in the upper 60s to mid 70s.

Adjusted timing of hourly POPs to match current radar trends
and bumped QPF a bit higher based on latest CAM output. This
resulted in very little change to the previous forecast.
Instability will remain very limited on the eastside of the
Allegheny Plateau, but with PWs reaching 1.5" and mean flow
<20kts in the lower half of the atm (sfc-500mb) there could be
some very localized downpours capable of producing spot amounts
>1 inch.

Shortwave tracking ENE from WV will help expand rainfall to the
east late tonight into early Saturday morning. Moist southeast
upslope flow will enhance rainfall in some of the favored
terrain while also supporting low clouds/cigs and fog. 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 /SATURDAY THROUGH MONDAY/...
Another wet start to the weekend with plenty of clouds, periods
of light rain/showers, and areas of fog. Hires model data
focuses the bulk of the rain early in the day, becoming more
scattered through the afternoon into the evening. Cool air
damming (CAD) pattern with moist east southeast flow will
result in highs ranging from 70-75F in the far NW mtns (5F above
climo) to 60-65F across the southeast half of the CWA (5-10F
below climo). Continued to temper NBM with blend of raw hires
model data given typical downside risk for cooler temps in this
type of CAD pattern setup.

We remain increasingly optimistic that Sunday will turn out to
be a much nicer day vs. Saturday. With the arrival of lower pwat
air and more northerly wind component along with ridging at the
sfc and aloft, odds favor a mainly dry and warmer end to the
weekend with some breaks of sun especially across the northern
tier. Latest model data indicates highs recover +5-10F across
the board with max temps around 80F fcst in the NW Alleghenies.

Look for areas of fog both Saturday night and Sunday night.

Temps continue to trend warmer into early next week with highs
on Monday reaching the upper 70s to mid 80s. High pressure
continues to build over CPA promoting rain-free conditions to
start next week.

&&

.LONG TERM /MONDAY 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 /17Z 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...Steinbugl
NEAR TERM...Steinbugl
SHORT TERM...Steinbugl
LONG TERM...Banghoff
AVIATION...Evanego