Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 300643
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
243 AM EDT Sun Apr 30 2017

.SYNOPSIS...
A nearly stationary frontal boundary will remain over the
forecast area for much of the weekend. A strong Cold front will
move across the region on Monday, followed by cooler air for
midweek.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Weak shortwave, which brought showers to northern Pa late this
afternoon, has passed into New England this evening. In its
wake, expect a dry evening beneath building upper level ridge
centered off the southeast coast. At the surface, a shallow cold
front along the I-80 corridor is pushing south across the
region. Temperatures at 01Z ranged from 51F at BFD to 77F at
HGR. This boundary is progged to stall out as it reaches the
Mason Dixon Line around midnight.

Increasing WAA above the stable boundary layer is indicated by
late tonight, as southerly low level jet works eastward from the
Ohio Valley. Have used blended POPs to bring a small chance of
showers/tstorms back in for the second half of the overnight,
mainly across the western counties. Blend of latest HRRR/LAMP
support min temps from the chilly mid 40s along the NY border,
to the low 60s near the stalled front along the southern border.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/...
The stalled front will lift north as a warm front across
western Pa Sunday, but remain hung up along the spine of the
Appalachians. Near term deterministic models show a cool-air
damming scenario hanging rather tough. The surface based LI
field is usually a great indicator of this. The ECMWF/NAM/GFS
are all in good agreement with the warm air working into my
western higher elevations while the ridge-valley areas east of
the Alleghenies stay in the clouds and cooler air. Have lowered
max temps toward the 18Z Superblend, but additional adjustments
downward are possible given the expected cloud cover and
southeast flow. 18Z NAM surface temps only reach the upper 50s
to mid 60s over much of central Pa Sunday. For now will take the
conservative route with highs from around 60 in the Poconos to
around 80 in Confluence, Somerset county.

For most of central Pa, it appears the best chance of showers
will be early in the morning, associated with 850-500mb WAA at
nose of low level jet. This feature lifts north of the region by
midday with weak large scale forcing to follow during the
afternoon, as inferred by model 500-300mb QVEC convergence
fields. Thus, there appears to be little chance of additional
rainfall across much of central Pa during the afternoon.
However, diurnal heating of the airmass west of the Alleghenies
should yield scattered late day convection across western Pa,
which could affect our western counties.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Upper level ridge builds across the Mid Atlc Region Sunday
night and Monday and a warm front will be lifting through the
Ohio Valley and W PA. This weather feature will lead to
continued chances for showers and even a tsra - mainly in the NW
half of the area. Upper low now over the four corners region is
forecast to lift through the central Plains on Sunday then the
Great Lakes on Monday. This will serve to send pieces of energy
along the surface boundary.

Temps should return/rise to very very warm levels on Monday. The
massive and deepening cyclone lifting into the western Great
Lakes Sun night into Monday will push a strong cold front
through PA Mon into Mon night, accompanied by a round of
potentially potent showers and thunderstorms (likely reaching
western half of CWA in the afternoon and eastern half during the
evening).

Once this front passes by much chillier air will advect into PA
on cyclonic flow with unsettled light showery weather persisting
mainly for the northern part of the state right into Wednesday.

Chance for a more widespread light rain arrives Thu into Fri as
a low progged to develop along the southern Appalachians and
the lift northward. Models showing strength/timing issues so
not getting to specific this far out, but looks like unsettled
weather pattern continues.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
30/06z TAFs followed LAMP/HRRR idea of developing sub-VFR low
clouds across much of the airspace this morning as boundary
layer flow veers to the southeast. The short-term guidance
shows a gradual erosion of sub-VFR cigs by the afternoon but
that may be too optimistic especially over the eastern 1/3 of
the airspace. The southeast flow should provide for stable
conditions to the east of the Alleghenies and therefore shower
risk is pretty low/isolated. The best chance for T`storms will
be along/west of the Alleghenies this afternoon/evening or
along/west of a line from KJST-KBFD.

Outlook...

Mon...Breezy. Showers/thunderstorms likely with periods of
sub-VFR. A few strong-severe storms possible wrn 1/2 Monday
afternoon/evening. FROPA Monday night.

Tue-Wed...Breezy with a chance of showers NW.

Thu...Widespread sub-VFR with rain likely.

&&

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

&&

$$
SYNOPSIS...La Corte
NEAR TERM...Fitzgerald
SHORT TERM...Fitzgerald/La Corte
LONG TERM...Lambert/Gartner
AVIATION...Steinbugl



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