Area Forecast Discussion
Issued by NWS State College, PA
FXUS61 KCTP 251828
Area Forecast Discussion
National Weather Service State College PA
228 PM EDT Sat Mar 25 2017
A cold front will sag southward across Pennsylvania this
afternoon and tonight, before returning north as a warm front
late Sunday and Sunday night. Unsettled conditions will continue
through the middle of next week before high pressure returns
with drier air.
.NEAR TERM /THROUGH TONIGHT/...
Meso-anal shows an west-east boundary strung out just north of
I-80. The thickest clouds are over northern PA along and north
of the front with brighter skies over southern PA where a mix of
sun and clouds is common. The boundary will continue to settle
slowly south throughout the day so by mid afternoon, it will
actually start to cool over the northern half or so of the
forecast area. The HRRR suggests that by nightfall it will have
moved through southern PA, with the possible exception of the
Rainfall amounts are expected to be on the light side. More
likely we will see a pattern developing where we have widespread
low clouds with scattered rain showers and areas of drizzle and
Overnight lows will range from the mid 30s over the NE to mid
40s over the SW. These will average some 10-20 deg above normal.
.SHORT TERM /SUNDAY/...
The light showers...with areas of drizzle/ridge top fog
are likely to continue through much of the day Sunday.
Local experience suggests we lean away from blended model
guidance for max temps in such low level cold air damming
situations. As such, I lowered tomorrrow`s highs by a few
degrees counting on a day not nearly as nice as today,
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
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 Sunday into early Monday. It
has a good surge of moisture and a boundary related to the
cooler weather on Sunday. Thus nearly all guidance shows a very
high probability of rain overnight Sunday 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 may be too high but they are consistent with
nearby offices. GEFS implies little or no rain in our CWA much
after 1800 UTC. Most rain before than 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 up to our west comes in overnight Monday
into Tuesday. Clearly the uncertainty with this and the longer
forecast length introduces more uncertainty. But at this time
peak rain probabilities are during the day Tuesday but lower
probabilities than the first event.
The second event will push the warm moist air 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.
The storm track shifts to our south and some models show a
southern stream wave Thursday night and Friday. This could bring
clouds to our region. GEFS and CMCE imply we could be on the
northern edge of an expanding precipitation shield Friday and
Saturday as the southern stream wave slides to our south and
east. Thus POPS increase Friday and Saturday. Could be a cold
rain across south-central PA Friday and Friday night.
.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
Frontal boundary over northern PA will be pushed southward
through the airspace toward the PA/MD line by 25/00z as strong
high pressure builds over eastern Canada. Increasing low level
moisture and wind shift to the east-northeast should translate
into a lower trend in ceilings and visibility from north to
south with widespread MVFR to IFR restrictions likely by
tonight, lasting into Sunday.
Scattered light rain showers will be possible today especially
near the southward-moving frontal zone with pockets of
fog/drizzle overnight into early Sunday morning. The front
should lift back to the north on Sunday which should allow for
at least some marginal improvement especially over portions of
the southern airspace.
Sun...VFR-MVFR western 1/4 with low risk for thunderstorm in the
evening. MVFR-IFR central and east with drizzle/fog.
Mon-Tue...Sub-VFR with periods of rain.
Wed-Thu...Becoming VFR. No sig wx.
NEAR TERM...La Corte
SHORT TERM...La Corte