Area Forecast Discussion
Issued by NWS State College, PA-- Remove Highlighting --
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FXUS61 KCTP 271202
Area Forecast Discussion
National Weather Service State College PA
802 AM EDT Mon Mar 27 2017
An area of low pressure will be moving northeast across the
Upper Great Lakes region this morning, pushing a warm front
northward across the District.
Unseasonably mild conditions are expected this afternoon
Cooler and dry weather will follow for Wednesday and Thursday.
A new storm system will approach for the end of this week,
brining with it a cold rain, that could be mixed with some wet
snow at times across the highest elevations.
.NEAR TERM /UNTIL NOON TODAY/...
Low-level cold air damming remains across the region this
morning while several areas of mdtly strong uvvel were support
mdt to heavy rain showers (esp across central and western PA)
where NAM shows the best 925-700 mb Theta-E convergence via a
core of 45-50KT mean winds in the 925-700 mb layer.
As this attendant southerly low-level jet continues to overrun
the dome of cool air across central Pa, expect rain to
continue to spread NE across the region between through much of
the morning hours. Mean 925-850 mb wind will veer to the SW then
West by late this morning and weaken substantially as the sfc
warm front tries to lift NE through the Central mtns. LAV and
MET MOS guidance shows plenty of clouds lingering today after
the periods of steadier rain taper to isolated showers by noon
EDT. The model guidance also indicates a quick rebound/warmup
in temps back into the 60s to near 70 deg F in the south this
A blend of near term models support POPS near 100 pct to start
the day, with additional rainfall amounts (mainly this morning),
averaging between one-tenth and one-quarter of an inch. lesser
amounts of rain will be seen across the far northwest and
southeast parts of the state.
.SHORT TERM /NOON TODAY THROUGH 6 AM TUESDAY/...
Morning showers should shift north and east of the region, as
the upper shortwave and associated low lvl southerly jet exits
the area. Low level stability indices indicate that the surface
warm front will lift northeast across the CWA by midday, as it`s
associated sfc low moves down the St. Lawrence River Valley.
Model soundings support lingering low clouds across the
northwest mountains, where southwest flow rises over the higher
terrain. Elsewhere, expect brightening skies with breaks in the
cloud layered cover by midday. The most sunshine is expected
over the southern valleys. The partial sunshine, combined with
ensemble mean 850mb temps of around 7C, should support max temps
in the low 70s across the southern valleys. The greater amount
of cloud cover expected across the northern half of the state,
will limit maxes there to be mainly in the 60s.
.LONG TERM /TUESDAY THROUGH SUNDAY/...
This period starts out with above normal heights over the
eastern U.S. Several lows weaken as they move into this blocked
flow and are forced to move to our west.
The first wave is comes through early today. It has a good
surge of deep layer moisture preceding it, and one or more
distinct ribbons of llvl theta-e convergence that have resulted
in some quasi north-south oriented bands of briefly heavier
showers. Most of the guidance shows the peak chance of rain
ending from SW to NE across the region between 0900-1400 UTC
today. improving conditions will follow for the midday and
afternoon hours today.
The second wave moving northeast and right up the Ohio River
Valley comes in overnight tonight across the western part of the
state, and Monday into Tuesday over the eastern half or so of
Another similar surge of +2-3 sigma Pwat air precedes the
passage of this area of low pressure and will once again result
in a high probability for showers, but generally light to
locally moderate 12 hour rainfall amounts.
This second ares of low pressure will push the warm moist air
off to our south Tuesday night into Wednesday. Chance of rain
should drop overnight Tuesday into Wednesday. Wednesday should
be a relatively nice day (though with some mdt northerly wind
gusts at times, as high pressure builds in from the northwest.
The dry air and high pressure are in all of the most recent
guidance, implying Wednesday and Thursday should be relatively
High pressure, dry air, and normal to slightly below normal 850
hPa and 925 hPa temperatures imply near normal daytime highs.
Most of the 26/00-06Z U.S. and int`l model guidance (and EFS)
indicates more of southern...shearing storm track for late in
the week...thanks to a stronger and more wwd position of a deep
nrn stream vortex across the Canadian Maritimes.
The trend of the big model discrepancy for late this week and
this weekend (between the GFS and EC over the past several days)
has trended toward the GFS and its ENS members with southern
stream energy and its moisture being prevented from amplifying
with an associated storm track to our west.
Rather, what we see is a shift of the primary southern stream
sfc low track to our south as the potent midweek southern stream
sfc/upper low (that will be trying to take the turn northeast
across the Mid Miss Valley twd the Great Lakes) encounters great
resistance from the notably stronger WNW upper jet core
defining the northern stream that will be situated from the
Upper Glakes to the Mid Atl Coast.
With this type of consensus storm track, pops will be somewhat
less for Friday and Saturday (compared to a heavily weighted
EC/ECENS solution) and limited to mainly the southern half of PA
where some rain (or even an elevation-dependent rain/wet snow
mix) with expansive cooler and drier air north of PA.
.AVIATION /12Z MONDAY THROUGH FRIDAY/...
-- Changed Discussion --LMVFR to LIFR conditions will continue through mid-late morning
with scattered rain showers exiting the eastern 1/2 of the
airspace/ZNY sector. Expect improving trend into the afternoon
with MVFR to VFR conditions likely after 27/18z. VFR should
hold for the most part into early tonight with guidance showing
restrictions developing into early Tuesday morning. Confidence
is low after 28/00z.
Tue...VFR/MVFR with periods of rain.
Wed...MVFR NW 1/3 becoming VFR.
Thu...VFR/No sig wx.
Thurs night-Fri...Sub-VFR restrictions/rain likely.
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