499
FXUS61 KCTP 230546
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
146 AM EDT Mon Sep 23 2024

.SYNOPSIS...
Welcome to Autumn! An amplifying upper level trough and slow
moving frontal boundary headed our way from the midwestern
states will bring several periods of rainy conditions across
Central Pennsylvania beginning Monday morning and lasting
through at least Wednesday.

&&

.NEAR TERM /THROUGH TODAY/...
A veil of mid and high clouds has increased over central and
eastern portions of central PA early this morning. Lower cigs
are found over the NW/WC Mountains and Laurel Highlands and now
spilling eastward into the NC and C mountains, with light
rainfall moving into the NW Mountains. Regional radar mosaic and
gage reports indicate most of the initial reflectivity returns
are aloft and only T amounts reported south of Erie in the past
1-2 hours.

Clouds will continue to increase, thicken and lower overnight.
Temps should again stay much warmer than normal tonight, with most
places at least 10F above normal. The approaching sfc frontal
system runs into the CAD in place over Central PA and stalls, so
eastward progression of whatever precip does make it into the
Alleghenies overnight will be a chore. Still, moisture transport
aloft is continuous overnight and rain/showers will eventually
spread across much of the western half of our CWA through
sunrise.

The plume of moisture overhead continues eastward and hangs over
the CWA most of the day on Monday. Heavy rain signal is not
there, but there might be a thunderstorm or two, more probable
in the SW than E. Temps on Monday won`t go more than 10F above
the morning numbers. Some places may not get much more than a 5F
deg diurnal swing.

Highs Monday will be mainly in the low to mid 60s in most
places, except for around 70F across the Lower Susq Valley.

&&

.SHORT TERM /TONIGHT THROUGH 6 PM TUESDAY/...
The 5H ridge axis doesn`t go east of our longitude, so the
showers might not get to the far eastern reaches of the CWA
early Mon night before fizzling. Another minor surge of WAA and
moisture aloft arrives in the Laurels before sunrise Tuesday.
So, the chcs for rain increase once again. PWATs get around 1.5"
Mon aftn before dipping then rising again later at night. The
storm motion doesn`t seem slow enough to make a widespread risk
of flooding. Basin average QPF total is only 0.5-0.75" at
highest. But, any storms can drop that much in a short time with
PWATs in that range. Still, a big factor against any flooding
is the very dry antecedent conditions, esp in the Laurels.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Model guidance outlines another surface low-pressure system
tracking northeastward across western portions of the Upper Ohio
Valley and into southern Ontario Tuesday into Wednesday, with
slightly more moisture and lift available as the warm front
aligns itself north-to-south across west-central PA. Given
slightly better lift with this low-pressure systemoverhead co
coupled with enhanced moisture, have retained likely PoPs in the
Tuesday to Wednesday timeframe. Given PWATs in the 1.25-1.75"
range on Wednesday, locally heavy rainfall will be possible with
relatively slower storm motion also possible. This threat has
been outlined with marginal (level 1/4) risks in the D3 (area
wide) and D4 (SE 1/2) Excessive Rainfall Outlooks from the
Weather Prediction Center. Highest impacts are expected to be
across areas that have recently received heavy rainfall, such as
urban areas of the Lower Susquehanna Valley, along with hydro
sensitive areas across the northern tier.

Model uncertainty in previous packages still remain late
Wednesday/early Thursday and into the end of the long-term
period, so there is low confidence as we move past Thursday
morning on this forecast cycle. A (potentially) slower
progression of the departing low- pressure system retains
chances through Thursday, with slightly lower chances as we move
into Friday.

The remnants of a tropical cyclone could also bring about rain
chances this weekend, but uncertainty with respect to
interactions with a trough that could limit chances of
precipitation/increase chances as we get closer to an event.

At this time range, have maintained numbers close to NBM
guidance which continues to paints SChc PoPs (~15-25%) or below
across the western PA with some enhancement of precipitation
along the Laurels.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
06Z TAFS sent.

Not a lot of change from the earlier TAF package. Band of
showers coming in a bit faster. The rain will tend to lower
conditions during the day, but time of day will tend to offset
the lower conditions a bit. By sunset I would expect conditions
to lower again.

The main feature on the weather map early this morning is a
weak low over western Lake Erie. Trend for the next few days is
for the frontal system to remain near the area. Thus I would
expect similar conditions each day for most of the week. While
VFR conditions may occur at times, I would expect this to be
for brief periods of time.

Outlook...

Tue-Wed...Chc/Likely SHRA with some TSRA possible.

Thu...Lingering/scattered showers possible area wide.

Fri...Scattered SHRA SW PA; otherwise, trending drier.

&&

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

&&

$$

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