805
FXUS61 KCTP 080041
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
841 PM EDT Sat Jun 7 2025

.SYNOPSIS...
* A cold front over Southern PA will push south to the
  Mason/Dixon late today through tonight.

* A few narrow bands of showers and perhaps a brief thunderstorm
  will develop in the warm and humid airmass along and to the
  south of the front.

* Low pressure will develop over the OH Valley and cross the
  Mid-Atlantic on Sunday, spreading additional storms and
  perhaps more heavy rain up into PA.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
830 pm/0030z update...The surface cold front has edged south of
the Mason-Dixon line this evening, with all convective activity
now removed from central PA. However, this boundary should soon
hang up once again, with another upper-level disturbance on
approach from the OH Valley. Higher level cloudiness is already
streaming into the region out ahead of this feature. Our
current forecast has showers moving back into the Laurel
Highlands towards daybreak, and this seems reasonable based on
the latest model guidance.

Concerning heavy rain potential on Sunday, with the slow
approach of the above mentioned upper-level trough, as well as a
developing E-SE low-level flow, occasional heavy showers could
develop, particularly in the upslope areas of the Laurel
Highlands and south-central mountains. For now, we`re going to
continue to hold off on a Flood Watch and monitor near-future
observational and model trends. Two things perhaps going against
an excessive rain event Sunday are: 1) The progged magnitude of
the low-level jet (15-25 kt, as opposed to the sustained and
focused 30-40 kt we saw with the flooding events in this same
general region back in mid-May, and 2) Potentially weak to non-
existent instability within an easterly flow cool air damming
pattern. As alluded to, we`ll continue to reassess this
situation overnight and into Sunday.

Also of note overnight into Sunday is wildfire smoke that has
once again gotten steered into the Commonwealth. As opposed to
fairly recent intrusions of wildfire smoke, this time
concentrations are greater in the lower-level of the atmosphere,
so haze and even a smoky smell to the air is more noticeable.
Guidance from the HRRR vertically integrated smoke model suggest
that the haze/smoke will stick around overnight into the early
morning hours, before it perhaps gets steered west of the
region with time on Sunday.

Previous discussion... 19Z surface analysis showed a cold front
stretched across the southern tier of PA, accompanied by a
narrow east/west bkn line of showers. Any convection deep enough
to cause lightning was confined just to the east of Lancaster
County over the past hour or so, where Sfc-based CAPE was
slightly higher and above 1500 J/KG.

Any rainfall from this point on through tonight will be limited
to generally near or south of the PA turnpike and amount to only
a few to several hundredths of an inch.

Though sfc dewpoints in the wake of the cfront have fallen into
the mid 50s to low 60s, deep layer flow veering to a more
North/Northwesterly direction has advected thicker smoke from
the Central/Western Canadian Wildfires SE into the area, and
we`ve seen vsbys unchanged (or even dip by a few miles) with
increasing haze from the smoke. The southern edge/lower
concentrations of Vertically Integrated Smoke via the HRRR
confirm this.

The brief ridge and area of dry conditions across the CWA
late today and tonight will yield to a thickening/lower shield
high, then mid clouds by daybreak Sunday.

Overnight lows will vary from the comfortably cool 50 to 55F
range across the Northern Mtns to the low 60s along the PA/MD
border.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY/...
Low pressure develops over the OH Valley and rolls just to our
south on Sunday. The most likely scenario out of this pattern is
a slug of rain and possible embedded thunder moving across our
southern tier. Many models and WPC guidance place the heaviest
rain on Sunday right over our CWA.

NAM and GFS differ on the location of the best precip. The NAM
generates the most QPF in our srn half, particularly the SE. The
GFS lingers the weak warm front/occlusion to our west a little
longer than the NAM. This difference results in a low-
confidence forecast for the threat for heavy rainfall. But, the
PoPs are easily categorical (80+%) for the S and E on Sunday and
Sunday evening. Temps will be 3-5F cooler than today, nudging
us below normal.

With respect to rainfall amounts, HREF 24 hour PMM totals are
generally less than 0.50 of an inch through 12Z Monday across
the NW Mtns and eastern Third of our CWA, with the Laurel
Highlands seeing locally 1.25 to 1.5 inches. These values are
still 0.25-0.50" or more respectively below 6 and 24 hour FFG,
so no huge concerns for a small stream/creek flood threat ATTM.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Unsettled weather pattern continues into Monday and Tuesday
with rounds of showers and thunderstorms likely as an amplified
upper trough across the Central US and Ohio Valley shears NE
across the Glakes Region by the middle of the week.

Went a decent amount beneath previous forecast highs Monday and
nudged temps down a significant amount toward the NBM`s lower
percentile values as plenty of thick clouds, some showers (or
morning drizzle) and a light, cool easterly breeze will likely
occur between a weak coastal low and the next shortwave (closed
upper low over the Upper Glakes at 00Z Tues). Temps should be
limited to the mid and upper 60s over the Northern Mtns and
Western Poconos and generally low to mid 70s elsewhere.

the best chance for shower/scattered TSRA will come late
Monday/Monday evening over the west and during Monday night and
early Tuesday morning across the Susq Valley and points east.

SFC and upper level ridging overhead and to our west will bring
drier and warmer conditions for much of the period Tuesday
night through Friday, although we can`t rule out a shower or
thunderstorm particularly across the north (30 pct chc) Thu-Fri
with a slow moving sfc cold front nearby. The chance for rain
increases across the area Saturday as the cold front pushes
southward first and then returns as a warm front, per latest
guidance.

&&

.AVIATION /01Z SUNDAY THROUGH THURSDAY/...
SFC cold front with notably lower dewpoints to its north will
drift just south of the PA/MD state line this evening.

A few brief showers Possible INVOF KLNS and KJST through dusk,
then dry for most or all of the overnight hours with some MVFR
vsbys in light fog/haze likely late tonight until around sunrise
Sunday. Cloud-wise any BKN, VFR moderate cu late today and this
evening will fade and be closely followed by a thickening shield
of high, then mid clouds from the west overnight.

Outlook...

Sun...Conditions lowering to mainly MVFR Sunday with the next
round of showers/t-storms beginning across the SW (KJST and
KAOO) during the mid-late morning hours Sunday and spreading
NE across the remainder of Central and Eastern PA Sunday
afternoon into Sunday night.

Mon-Tue...Unsettled pattern continues with additional rounds of
showers and t-storms. Widespread low cigs (IFR to MVFR) likely
in a light.cool moist East/SE low level flow on Monday. A few
rounds of showers during the day, with some areas of morning
drizzle.

Wed and Thursday...VFR. Isolated PM showers/storms Thursday
across mainly the Northern Mtns of PA.

&&

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

&&

$$

SYNOPSIS...Lambert/Dangelo
NEAR TERM...Jurewicz/Lambert/Dangelo
SHORT TERM...Lambert/Dangelo
LONG TERM...Lambert/Colbert
AVIATION...Lambert/Dangelo/Tyburski