Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 262147

Area Forecast Discussion
National Weather Service State College PA
547 PM EDT Sun Mar 26 2017

A cool-moist easterly flow will keep it damp over most of the
forecast area. A frontal system will move back into the region
overnight and remain nearly stationary before a cold front
finally ushers in cooler and drier air during the day Tuesday.

The drier conditions will continue for mid week before a new
storm system approaches for the end of the week.


The region remains firmly ensconced in a low level cold air
damming pattern late this afternoon. New high resolution GOES-R
1 minute visual loop shows the stable low clouds being passed
over by the more broken mid and high clouds. The only part of
the area not locked into the cold air damming is Warren County,
where some sun is helping temperatures climb into the mid 50s.

Regional radar loop at 2030Z showing first band of showers
moving into the Laurel Highlands associated with approaching
shortwave. HRRR and 18Z NAM show southerly low level jet lifting
across central Pa overnight, resulting in an increasing
likelihood of rain over the central counties early this evening
and east of the Susquehanna River after dark. Blend of near
term models support rainfall overnight of between a quarter and
half inch over much of central Pa, with a bit less over the
Lower Susq Valley. Although just about the entire region will
remain in stable air east of stationary front, models indicating
enough elevated instability ahead of shortwave to perhaps
support a few rumbles of thunder overnight, mainly across the
western counties.


Low level stability indices indicate that the the surface warm
front will try to lift NE across the CWA late tonight and Monday
morning as it`s associated sfc low moves down the St. Lawrence
River Valley as a weakening feature.

The new GFS and NAM suggest that a lull in the shower activity
will take place late tomorrow morning and afternoon as the
remnants of the diffuse warm frontal boundary fall apart over
northern PA/southern NY in favor of the stronger thermal
pattern that re-establishes south of the region ahead of an
approaching new storm system. This leaves a weak flow pattern in
place for the afternoon, likely still more clouds than sunshine
but with the chance for some breaks helping temperatures
returning to something much more palatable than today`s chilly
40s. Highs should make it into the mid 50s, and range to the
lower 70s along the MD border.


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 overnight tonight into early Monday. It
has a good surge of moisture and one or more distinct ribbons
of llvl theta-e convergence that should result in some nearly
north-south oriented bands of briefly heavier showers. Thus
nearly all operational and blended/ensemble guidance shows a
very high probability of rain overnight tonight into Monday.
Most of the guidance shows the peak chance of rain from
0000-1200 UTC Monday. Then things improve during the day Monday.

The second wave moving northeast and right up the Ohio River
Valley comes in overnight Monday into Tuesday. 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.

The second event 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 good day as high pressure builds in from the
northwest. The dry air and high pressure are in all the guidance
implying Wednesday and Thursday should be relatively nice days.

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.


First band of showers falling apart, as it moves into central
PA. Several more bands of showers over OH.

Made some changes to 21Z TAF package, some of which will be
used in the 00Z TAF package. Expect some improvement later
Monday, as winds shift more to the southwest.

Earlier discussion below.

A moist east/southeast low level flow will support widespread
low MVFR to LIFR conditions into Monday. Aside from pockets of
drizzle/mist/fog, the main period of rain should be tonight
between about 27/00z to 27/12z, tapering off from west to east
Monday morning.

Conditions will improve slowly later Monday morning with central
and eastern terminals likely rising to VFR by early to mid
afternoon. A stray afternoon thunderstorm cannot be ruled out,
especially over the south.


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

Wed...MVFR becoming VFR early.

Thu...VFR early, Increasing chance of rain and lowering
conditions late in the day into Thursday night.

Fri...Breezy with showers. MVFR to IFR conditions possible.




NEAR TERM...Fitzgerald/La Corte
LONG TERM...Grumm/Lambert/Gartner
AVIATION...La Corte/Martin is the U.S. government's official web portal to all federal, state and local government web resources and services.