828
FXUS61 KCTP 121024
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
624 AM EDT Sun May 12 2024

.SYNOPSIS...
Upper level troughing will remain over Pennsylvania this
weekend with a potent shortwave tracking over the state tonight
into early Sunday. The upper trough will lift out early next
week, then a cold front will likely push through Tuesday. A wave
of low pressure is likely to track south of Pennsylvania next
Wednesday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
08Z water vapor loop shows a vertically-stacked low pressure
system over Eastern Lk Erie. At the surface, an occluded front
extends south from the low, running just west of KIPT and KTHV.
The attendant low level jet and area of most concentrated
showers has pushed east of the forecast area. However, low level
instability associated with the upper low will yield scattered
showers through the morning hours.

All guidance indicates the upper low will exit Southeast PA by
late morning. However, cold temps aloft should result in
scattered diurnally-driven showers over most of Central PA into
the afternoon, with a focus along the lingering occluded front
over the eastern part of the forecast area. Convection-allowing
model guidance indicate low level convergence along this
boundary will support the best chance of showers and perhaps an
isolated tsra in a corridor running from from Tioga County south
through York County. Brightening skies and diminishing showers
look likely by late this afternoon, as heights rise in the wake
of the departing upper trough.

Mixing down progged 850mb temps of around 4C translates to
expected highs in the low to mid 60s over much of the forecast
area. However, mainly overcast skies and a southeast flow off
of the Atlantic should keep the eastern edge of the forecast
area cooler. The higher elevations of Sullivan/Schuylkill
Counties will probably do no better than the low 50s.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/...
Surface ridging building into the region tonight and the
associated clearing skies/light winds, combined with wet
ground, should promote valley fog development. Ensemble prob
charts indicate the eastern part of the state is likely to see
the most extensive fog, which could develop as early as late
evening.

Upper level ridging building over PA should result in a warmer
and drier Monday overall. However, a weak area of low pressure
and its attendant warm front lifting through the Eastern Grt Lks
could produce a few morning showers or afternoon tsra across the
northern half of PA. Partly sunny skies and a developing
southwest flow should push readings into the low to mid 70s.

A wave of low pressure will approach from the Ohio Valley
Tuesday before crossing the area Tuesday night, accompanied by a
renewed chance of rain and perhaps some thunder.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Lingering unsettled weather is possible into Wednesday, as
upper-level low pressure passes overhead.

Medium range models diverge a bit late next week. The 12z ECMWF
shows unsettled weather persisting into Thursday, as the upper-
level low pressure very slowly pulls to our east. The 12z
GFS/GEFS is a bit more optimistic, showing an upper-level ridge
bringing a period of dry weather from Wednesday night through
early Friday.

Both medium range models are in agreement in bringing our next
weather maker into the area later Friday into Saturday with
another round of showers and thunderstorms.

&&

.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
A variety of conditions are present across the airspace as rain
showers continue to drift east along the occluded front. A few
of these showers could have moderate rainfall, and low clouds
will keep some sites at MVFR to IFR during the early morning
hours.

Northwesterly flow develop across the area today as the surface
low passes overhead and drifts to the south east, with gusts to
15 kts possible across the southern Alleghenies (JST, AOO).
Cigs should slowly improve as the day progresses, with the
slowest improvement expected across the western highlands. There
could be a few diurnal rain showers by afternoon, esp across
eastern PA.

Outlook...

Mon...Morning fog across the east/Susq Valley. Showers return
across the north by aftn.

Tue...Showers/tstms and reductions developing.

Wed...Showery weather and reductions continue.

Thu...Slow improvement, with a few lingering showers possible.

&&

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

&&

$$

SYNOPSIS...DeVoir/Dangelo
NEAR TERM...Fitzgerald
SHORT TERM...DeVoir/Fitzgerald
LONG TERM...Banghoff/Evanego
AVIATION...Evanego/Bowen