Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 251800
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
200 PM EDT Sat Mar 25 2017

.SYNOPSIS...

A cold front will sag southward across Pennsylvania this
afternoon and tonight, before returning north as a warm front
late Sunday and Sunday night. Unsettled conditions will continue
through the middle of next week before high pressure returns
with drier air.

&&

.NEAR TERM /THROUGH TONIGHT/...

Meso-anal shows an west-east boundary strung out just north of
I-80. The thickest clouds are over northern PA along and north
of the front with brighter skies over southern PA where a mix of
sun and clouds is common. The boundary will continue to settle
slowly south throughout the day so by mid afternoon, it will
actually start to cool over the northern half or so of the
forecast area. The HRRR suggests that by nightfall it will have
moved through southern PA, with the possible exception of the
far SW.

Rainfall amounts are expected to be on the light side. More
likely we will see a pattern developing where we have widespread
low clouds with scattered rain showers and areas of drizzle and
fog.

Overnight lows will range from the mid 30s over the NE to mid
40s over the SW. These will average some 10-20 deg above normal.

&&

.SHORT TERM /SUNDAY/...

The light showers...with areas of drizzle/ridge top fog
are likely to continue through much of the day Sunday.

Local experience suggests we lean away from blended model
guidance for max temps in such low level cold air damming
situations. As such, I lowered tomorrrow`s highs by a few
degrees counting on a day not nearly as nice as today,
temperature-wise.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
The main precip event impacts central PA Sun night into early
Mon as low moves through. QPF looks to be around 0.50 inch.

Above average temperatures (especially nighttime) appear very
likely through early next week, as GEFS indicates PA remains
beneath a mean upper level ridge and plume of anomalous PWATs.

The chance of showers again spikes with passage of next
shortwave Tuesday into Wednesday and another one to start the
weekend.

U.S. 25/00Z and 06Z GFS and GEFS differs drastically with the
25/00Z EC and its ensembles during the second half of the week,
as the EC guidance is dominated by stronger southern stream
troughs and associated northward advection of warmer air and
higher 500 mb heights. In contrast, the GFS and its ensemble
mean appears to maintain a several decameter deeper and more
persistent upper low over nrn New England and the Canadian
Maritimes, while also latching onto a piece of northern stream
energy that breaks away from a potent upper low that will be
digging SE across the Four Corners area Tuesday, before heading
east across the High Plains of E New Mexico and West Texas
later Wednesday and Wed evening.

The presence of this aforementioned northern stream short wave
has big implications for maintaining/reinforcing colder NW flow
aloft across southern Canada and the NE U.S., while shearing its
initially potent southern stream "parent" low harmlessly east
(for us here in Central PA) across the Carolinas.

Considering the several-run persistence in the GFS, along with
the amount of snow cover across intact parts of the nrn Mid
Atlantic and New England States, (not to mention the persistence
of cold air there and points north across Ont and Quebec), I
slightly favor the GFS/GEFS solution at this point in time with
a more extended period of drier and cooler conditions for Wed-
Sat. The northern edge of the precip shield associated with the
shearing srn stream wave and mdtly strong forcing via the R.E.
region of a 100-120 kt upper jet across the Lower Great Lakes
and Mid Atlantic region may support a period of cold
rain...mix...or even a light accumulation of snow across the
southern half of PA late in the week.

The "Less likely" EC solution (at this point) would help to
develop a stronger upper ridge across the eastern U.S. for the
second half of the week with the upper low lifting NNE to the
upper midwest by 00Z Sat with warmer air at the surface and
aloft surging northward through the Ohio River Valley and
Appalachians.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...

Frontal boundary over northern PA  will be pushed southward
through the airspace toward the PA/MD line by 25/00z as strong
high pressure builds over eastern Canada. Increasing low level
moisture and wind shift to the east-northeast should translate
into a lower trend in ceilings and visibility from north to
south with widespread MVFR to IFR restrictions likely by
tonight, lasting into Sunday.

Scattered light rain showers will be possible today especially
near the southward-moving frontal zone with pockets of
fog/drizzle overnight into early Sunday morning. The front
should lift back to the north on Sunday which should allow for
at least some marginal improvement especially over portions of
the southern airspace.

Outlook...

Sun...VFR-MVFR western 1/4 with low risk for thunderstorm in the
evening. MVFR-IFR central and east with drizzle/fog.

Mon-Tue...Sub-VFR with periods of rain.

Wed-Thu...Becoming VFR. No sig wx.

&&

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

&&

$$
SYNOPSIS...La Corte
NEAR TERM...La Corte
SHORT TERM...La Corte
LONG TERM...Lambert/RXR
AVIATION...La Corte


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