Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 261548
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1148 AM EDT Sun Mar 26 2017

.SYNOPSIS...

A cool-moist easterly flow will make for a gray day 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.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

The region remains firmly ensconced in a low level cold air
damming pattern. 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 western Warren country where some
sun is helping temperatures climb into the 50s.

Max temps today were weighted heavily toward the NAM. The NAM
limits highs to the 40s for many locations...and even holds
readings in the upper 30s across some of the higher terrain
throughout the NE corner of our CWA. This is in comparison to
the much warmer (by 8-10 deg F) National Blend of Models where
its GFS core lacks the boundary layer detail to adequately
capture the shallow cold airmass being channeled through the
deep valleys of Central PA.

Have downplayed the chances for rain today as the nearest
organized precip remains well upstream. HRRR shows the chances
for rain increasing later in the afternoon over the west.
elsewhere other than some scattered drizzle, it will be just
cloudy and cool.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
An upper low an increased Diff PVA will approach from the Ohio
Valley late in the day, bringing a renewed chance of showers
across the Alleghenies and Central Mountains toward evening.
Can`t rule out a rumble of thunder across the Alleghenies,
although any convection will be weakening rapidly as it
encounters the shallow and very stable/cool airmass entrenched
throughout Central Pa.

Sfc warm front will try to lift NE across the CWA late tonight
as it`s associated sfc low moves NE across the Upper Great
Lakes. Widespread clouds and relatively mild temps will persist
overnight with lows in the 30s to low 40s.

Energy aloft and a core of 50 kt South-southwesterly accompanied
by a few bands of moderately strong low-mid level Theta-E
convergence will bring periods of rain with one quarter to one
half inch of rain falling. The heaviest rainfall will be over
the western mountains where localized amounts of 0.75 to 1.00
inch area possible.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
This period starts out with above normal heights over the
eastern US. 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 NCEP guidance shows the peak chance of rain from
0000-1200 UTC Monday. Then things improve during the day Monday.

Our POPS Monday morning may be too high, but they remain
consistent and well-collaborated with surrounding forecast
offices. GEFS implies little or no rain in our CWA much after
1800 UTC Monday. Most rain before then would be in the east.
Our 850 hPa temperatures are above normal too so should be a
warm later afteroon and evening.

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.

&&

.AVIATION /16Z SUNDAY THROUGH THURSDAY/...

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

Outlook...

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

Wed...MVFR with chance of rain early in the morning, then
becoming VFR.

Thu...Increasing chance of rain late in the day into Thursday
night.

&&

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

&&

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



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