Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 291124

Area Forecast Discussion
National Weather Service State College PA
724 AM EDT Wed Mar 29 2017

Cooler and drier air will overspread Pennsylvania today and
Thursday as high pressure builds southward from southern
Canada. A new storm system will approach the region on Thursday,
bringing showery conditions Thursday night through Saturday.
Cooler and unsettled conditions will last into Sunday, with
scattered valley rain and mountain snow showers possible.


Cooler and drier air mass filtering southward over central PA
early this morning. Low clouds persist across most of central
PA...but early morning IR imagery shows breaks evolving and back
edge settling southward through the Fingerlakes region. After a
cloudy start...expect to see sun breaks increase as the early
morning progresses. Building sfc high pressure will eventually
bring a mix of sun and clouds across northern areas, and a
bright sunny day over southern areas by mid to late morning.
Highs in the 40s and 50s will be near to slightly above normal.
It will be breezy out of the north between 10 and 20 mph.


Fair and cool conditions will continue tonight and Thursday...
as strong surface ridge axis remains nosed and anchored across
central PA tonight and Thursday. Clouds will increase by late
Thu morning and Thu afternoon from west to east (respectively)
as the sfc ridge axis moves offshore and return flow arrives.
Late day showers are expected to develop west of the Alleghenies
and may reach the central mountains by nightfall...which will be
the start of another lengthy stretch of gloomy and showery
conditions set to last through most of the weekend.

Mins tonight will be much chillier than recent nights..ranging
from the upper 20s north to the mid 30s south. Highs on Thursday
will be a few degrees cooler than Wednesday thanks to decreased
mixing and increasing cloud cover in the morning and afternoon
hours especially...and will range from the mid 40s north to the
lower 50s south.


GFS/EC and their respective ensembles are in good agreement
with the onset timing of warm frontal rain that streaks quickly
east from the Ohio Valley by Thursday evening.

Evaporational/dynamic cooling of the airmass *may* help 925-850
mb temps dip to near 0C across our NE counties Thursday night
and Friday as the steadier light- mdtly heavy, Warm Advection
rain begins there. 00z cycle has warmed boundary layer from
earlier solutions...and have included only isolated mentions of
rain/sleet mix to the North and East of a KIPT and KSEG line.
There`s a low prob for a light coating of snow on the high
terrain across Sullivan County...and have a few tenths of an
inch of snow accumulation forecast there.

Model consensus is also for a quasi Miller-B type of low track
heading just north of the Ohio River during the day Friday,
then a pressure jump and slight intensification of the sfc low
(to 996 mb) off the southern NJ and New England Coast Saturday.

Under normally colder winter-time circumstances, this low track
would be pretty favorable for a significant snowfall across
much of central and northern PA. However, a quite warm boundary
layer (and 850 mb temps) to begin with, coupled with the lack
of a stronger anchoring high over southeast Canada and New
England will mean a widespread/soaking rain evening with 24-36
hour rainfall at the majority of places here in Central PA
coming in between 0.75-1.00 inch.

This rainfall will add a healthy spike to the flow and levels on
smaller streams and creeks across the region with broader mdt
rises on rivers, but no significant threat for flooding as
headwater flash flood guidance is averaging 2-2.5 inches for a
12 and 24 hour period respectively.

Periods of light rain, drizzle, and ridge shrouding dense fog
will persist Friday night into Saturday as slightly colder air
wraps around behind the storm. Some breaks in the cloud cover
should occur Saturday afternoon, esp across the Lower Susq
Valley where drying downslope flow will be enhanced. Forecast
temps Friday may be a bit warm considering the aforementioned
storm track just to our south, and amount of rain expected.

Max temps Saturday will near to a few deg F above normal in
many locations.

High pressure building over the region (coupled with the
offsetting effect of abundant sunshine and GEFS mean 850 mb
temps cooling by 3-4 deg C imply max temps close to what we`ll
see Saturday, which is upper 40s to lower 50s across the nrn
mtns...and mid to upper 50s elsewhere. Dry and slightly milder
conditions are in the forecast for Monday as the ridge of high
pressure slides just to our east and ens mean 850 mb temps
rebound by a few to svrl deg C (atop a light serly sfc flow).

The next, rather potent and moisture laden southern stream wave
heads our way for Mon night and Tuesday, bringing a likelihood
of a widespread rain.


MVFR ceilings this morning improving to VFR. VFR conditions
will continue tonight into Thursday morning with increasing
high-to-mid level clouds/cigs AOA 10kft AGL.


Thu: VFR/No sig wx. Chance of rain NW 1/2 late.

Thu Night-Fri: MVFR/IFR. Rain.

Sat: Sub-VFR restrictions early; then gradually improving
conditions into Sat night.

Sun: VFR/No sig wx.




NEAR TERM...Grumm/DeVoir
SHORT TERM...Grumm/DeVoir
LONG TERM...Lambert/Gartner
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