Area Forecast Discussion
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FXUS61 KCTP 291205
Area Forecast Discussion
National Weather Service State College PA
805 AM EDT Sat Apr 29 2017
A nearly stationary frontal boundary will be located over
portions of Pennsylvania for much of the time this weekend. A
few disturbances aloft will move over this front and bring
periods of showers and thunderstorms. A strong trough and cold
front will move across the region on Monday, followed by much
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Fast-moving and the northeast member of a series of MCSs
(that stretched all the way back to the southern plains) has
exited our CWA and is heading quickly for the NJ coast.
Another batch of showers and perhaps a few rumbles of thunder
will affect far southern and western parts of the CWA during
the late morning hours as it races ENE and temporarily weakens.
Low temps around sunrise will range from the lower and mid 50s
across the NW half of the forecast area...to the mid 60s across
the Lower Susq Valley (that current lies close to the quasi-
stnry frontal boundary). These temps will be about 15-18 deg F
First front, separating the very warm and juicy airmass (where
temps will be in the 80s with dewpoints in the mid 60-lower 70s
this afternoon) extended from central WVA to extreme SE PA and
will be drifting a little further south into northern VA late this
morning. A second (cold front) extended from western Lake
Ontario Lake Erie and will be sliding into our far nrn zones
during the late morning and afternoon, with the central third of
the state sandwiched in between (in the Temperate Zone).
For the late morning and afternoon hours, the HRRR shows a few
weak sfc waves sliding east across the region about 30-50NM
south of the I-80 corridor. Marginal Risk for SVR TSRA across
the northern half of the CWA looks to be overdone, with any
thunder across that region coming in the form of elevated weak-
00Z-06Z NAM has trended at least 50-75NM further south with
significant sfc based cape and better low-mid level directional
shear and EHIs, so the main threat for any localized strong to
potential SVR tsra will likely be across the southern 1-2 layers
of PA counties.
Max temps are a blend of the more heavily weighted 29/06Z NAM
(70 percent) with about 30 percent 29/00Z Nat`l Blend of Models.
More singular nudging/weighting twd the NAM results in quite
chilly temps in the upper 50s to lower 60s across the nrn tier
counties of PA. Don`t want to jump the gun and go that low just
yet, but it`s pretty obvious that if the cooler models verify
better, it`ll be too cool/stable for significant/strong
convection. Potential for locally heavy rain of an inch or so
may be a different story across roughly the SW half to two
thirds of the CWA as more organized convection and another
possible MCS rides ENE across the aforementioned stalled out
pair of sfc-925 mb frontal boundaries.
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
29/06Z NAM guidance brings both of the previously noted frontal
boundaries gradually back to the north overnight and Sunday,
but maintains shallow chilly air across the Central and NE zones
as the elongated east/west 1022-1026 mb sfc ridge slides over
the middle St Lawrence River Valley by Sunday afternoon.
Again, the main focus for Sunday may be periods of heavy
rain showers/TSRA from elevated convection, while any sfc-based
updrafts stay limited to the south central counties and wrn mtns
near and to the west of RT 219. Sunday`s max temps will also be
weighted more heavily twd the cooler 29/06Z NAM with a 25
percent NBM blend afterward, which will lead to highs in the
mid to upper 70s over the west and south, and only low-mid 60s
in the far NE and wrn Poconos.
With dewpoints well up into the 60s over far southern and
western portions of the CWA, it will begin to feel humid.
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Upper level ridge builds across the Mid Atl 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
Temps should return/rise to very very warm levels on Monday. A
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
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
lift northward. Models showing strength/timing issues so not
getting to specific this far out, but looks like unsettled
weather pattern continues.
.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
The next wave of high-based showers and embedded tstms will
track across southern PA this morning. MVFR/IFR visibility at
MDT/LNS should improve with the onset of pcpn btwn 13-14z.
29/12z TAFs continued to rely on persistence, radar trends and
high res model consensus which still favors a predominately VFR
fcst at least through the first 1/2 of today. A quasi-
stationary frontal boundary will bisect the airspace by this
evening with MVFR cigs likely on the northwest side. Confidence
is low concerning pcpn trends for the afternoon but consensus
suggests isolated convection confined mainly over the SW
airspace. Areas of sub-VFR are possible tonight but coverage
should be limited.
Sun...Sct showers/Tstorms with sub-VFR restrictions possible
especially over the west-central airspace.
Mon...Breezy. Showers/thunderstorms likely with periods of sub-
Tue-Wed...Breezy with a chance of showers NW 1/2.