Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 261415
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1015 AM EDT Wed Jul 26 2017

.SYNOPSIS...
An expansive ridge of high pressure extending across the
central and northern Appalachians will bring us a pleasantly
warm day with comfortable humidity.

Mid level clouds will increase from the west tonight into
Thursday. A cold front will push gradually southeast across
the district late Thursday night through Friday morning with
numerous showers and isolated to scattered thunderstorms.

Another wave or two low pressure will likely form along this
front as it sags to the southern border of the state, bringing
some additional periods of rain Friday afternoon into Saturday
morning, mainly across the southern portion of Pennsylvania.

Another refreshingly drier and cooler airmass will overspread
the commonwealth this coming weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
For the late morning update, did cut back POPS some across
the far northeast. Did expand across the far east for the aft,
as CU are forming across the southeast, and some hints of
returns on radar and visible satellite pics near BWI.

Earlier discussion below.

1026mb sfc high centered over northern VT has a ridge extending
down along the Appalachians into PA early this morning.

A weak inverted trough and marine layer to its east was
producing some fairly thick low clouds and evening some light
showers/drizzle invof KRDG and KLNS. Mentioned isolated to sctd
SHRA in that part of the CWA this morning, but even these low
chcs decrease this afternoon as the mean low to mid flow becomes
south to southwest.

Elsewhere across central and western PA, today is shaping up to
be quite nice with abundant sunshine mixing with increasing mid
and high clouds late. Temps will be near normal across the
northern and wrn mtns, and a few to svrl def F below normal
elsewhere.

The 20-25F air/stream delta T has resulted in patchy dense
valley fog (mainly across nrn PA) where temps early today were
in the upper 40s to low 50s. Elsewhere, mins early today varied
from the upper 50s to lower 60s.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY NIGHT/...
Increasing dual to multi-layer clouds advect east/SE into the
state later tonight through Thursday morning with little more
than some scattered and brief showers drifting over the area.

Deep layer warm advection and a return to a notable higher PWAT
airmass will occur in advance of a cold front and another upper
deepening, but rather compact upper trough headed our way from
the Great Lakes region.

Anomalous PWATs on a SW to NE axis will top out between
1.5-1.75 inches over the state Thursday afternoon and night
before likely settling just south of the state on Friday.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
The last cycle or two of model run shows a highly anomalous
northeasterly flow in the sfc-850 mb layer developing Friday
into Saturday as a strengthening wave (or two) of low pressure
at the sfc develops/moves east from the Ohio River Valley and
passes near the Mason/Dixon.

Thick clouds and a strengthening north to nwrly ageostropic
llvl flow will combine with moderately strong llvl cold
advection to bring a quite chilly day for late July. Highs
Friday could struggle to climb above the mid 60s across the
higher terrain of the north and west, while highs in the Central
valleys come out to be in the low-mid 70s. The strength of the
expected sfc low shown by multiple models and EFSs and the
approximate -3 sigma 925-850 mb wind will be quite a rarity in
the Mid Atlantic region for Mid Summer. A significant severe
weather outbreak will likely occur near and just to the south of
the aforementioned sfc low track.

Q widespread light to moderate, chilly rain event (with locally
heavy amounts and elevated instability/thunder across the
south) is expected for Friday afternoon into Saturday morning,
followed by a chilly airmass for later Saturday into Sunday as
the northerly llvl wind anomaly strengthens to -3 to -4 sigma in
the wake of the deepening low just off the southern New England
coast.

Conditions eventually dry out later Saturday and Saturday night
with a gusty north to northwest wind as high pressure builds
in. Sunday and Monday appear mainly dry at this time as the
sharp mid level thermal trough slides off the Mid Atlantic
Seaboard.

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
As high pressure builds in from the west, shallow marine layer
under lowering inversion is developing a lower cloud deck over
the northern tier (KBFD), which will thicken through 12z. In
addition, a more widespread lower stratus deck over eastern PA
is edging back into the Susq Valley from the east. This lower
stratus deck will bring a period of MVFR to IFR conditions
into mid morning. If that`s not enough, in central areas
radiational cooling, combined with light winds, is bringing
formation of valley fog, with it`s own associated restrictions
in visibility and low ceilings through ~13z.

The clouds and fog will erode by mid/late morning, with VFR
conditions expected by mid day across entire region.

Tonight, mainly mid/high clouds thicken ahead of an approaching
system due on Thursday. But low ceilings could again sneak into
eastern terminals from eastern PA toward sunrise.

Numerous showers and scattered thunderstorms return for
Thursday afternoon and night with the approach of another cold
front.

.OUTLOOK...

Thu...VFR, but with restrictions developing in SHRA/TSRA.

Fri...Scattered SHRA north with more numerous and heavier
SHRA/TSRA across the south.

Sat-Sun...No sig wx.

&&

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

&&

$$
SYNOPSIS...Lambert
NEAR TERM...Lambert/Martin
SHORT TERM...Lambert
LONG TERM...DeVoir/Lambert
AVIATION...RXR



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