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881
FXUS61 KCTP 221824
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
224 PM EDT Sun Sep 22 2024

.SYNOPSIS...
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Welcome to Autumn! A slow moving weather system brings multiple
chances for rain to Central Pennsylvania for Monday through at
least Wednesday.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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Strato cu based around 2kft over Central PA in mid-Sept is not
unusual, but usually the wind is from the exact opposite
direction. These clouds will hang around and likely get
reinforced through the night with the constant SE flow in the
llvls. Probably not as much/widespread fog as Sun AM, due to
the clouds already being there. Temps should again stay much
warmer than normal tonight. Most places will be at least 10F
above normal. We`ll hold off for now mentioning drizzle for the
overnight, but there could be a patch or two on the windward
slopes of the ridges.

Similar to the last system, the approaching sfc frontal system
runs into the CAD in place over Central PA and stalls. Moisture
aloft and forcing keeps on flowing overhead, though and
rain/showers should get into the western zones around or even a
little before sunrise.
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.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
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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. 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 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.
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.LONG TERM /TUESDAY THROUGH SATURDAY/...
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 system coupled with
enhanced moisture, have retained likely PoPs in the Tuesday to
Wednesday timeframe. Given PWATs in the 1.50-1.75" range on
Wednesday, locally heavy rainfall will be possible and this has
been outlined with marginal (level 1/4) risks in the D4 (W) and
D5 (E) Excessive Rainfall Outlooks from the Weather Prediction
Center. Impacts at this time look less likely at this time given
ongoing dry conditions across especially SW PA where D2 drought
conditions persist; however, any heavier rainfall in the
preceding days could allow for slightly more impacts.

As we shift into the later part of the week, slightly more
model uncertainty with regards to low-pressure moving N/E of the
area and how this will impact rainfall chances for Central PA.
At this time, have capped PoPs at a chance for Thursday as the
low-pressure system will be slightly closer to our eastern half,
and capped at a slight chance for Friday, keeping close to NBM
model guidance in this timeframe.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
710 AM update.

Showers and storms southeast of the area. Fog has been hit
and miss overnight. Just now seeing some fog outside the office
during the last hour.

06Z TAFS sent.

More in the way of weather than I expected when I came in early.
Last of the storms now south of the TAF sites. Key to fcst seems
to be having southeast flow of slightly higher dewpoints with
a drier airmass building in from east. This happen a few weeks
ago. Storms get caught in similar locations, most likely aided
by terrain features.

Anyway, main issue will be fog and low CIGS overnight. Expect
conditions to improve during the day, but I did now bring
conditions up too fast, given time of year. First day of fall
today, so days are getting shorter with less intense sun to
burn off fog and low clouds as fast as back in the summer.

Setup for showers and storms similar to yesterday, but left
mention out of the TAFS for now. Less chance today, as dewpoints
fall off more. Also coverage of activity during the day time
on Saturday was rather limited.

Outlook...

Mon-Thu...Scattered showers, restrictions possible.

&&

.CLIMATE...
Autumn began at 8:44 am.

&&

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

&&

$$

SYNOPSIS...Dangelo
NEAR TERM...Dangelo
SHORT TERM...Dangelo
LONG TERM...NPB
AVIATION...Martin
CLIMATE...Earth