Area Forecast Discussion
Issued by NWS State College, PA
FXUS61 KCTP 010940
Area Forecast Discussion
National Weather Service State College PA
540 AM EDT Sat Oct 1 2016
A cut off upper low over the Ohio Valley will drift slowly to the
northeast over the next few days, clearing the region by early in
the upcoming week. A ridge of high pressure will build east into
Pennsylvania behind this system and will likely remain over the
area through the middle, and perhaps end of the work week.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Early morning IR/water vapor loop shows the cut off upper low
spinning over the Lower Ohio River Valley. Deep, moist east-
southeasterly flow ahead of this system continues to produce thick
stratus with areas of drizzle and higher elevation dense fog
across central Pa as of 09Z.
Primary shortwave and associated right entrance region of the 90
kt southerly 300 mb jet will support widespread drizzle and
periods of light to mdt rain across the western half to two-thirds
of the forecast area through the late morning hours. Rainfall
will average one tenth of an inch or less through 15z. However,
locations seeing a couple of heavier showers (especially over the
NW mtns) could pick up 3-4 tenths of rainfall in just a 15 to 30
Much of region east of the Middle and Lower Susq Mainstem will
stay dry this morning, with just some patchy drizzle or a brief
Temperatures will start out the day in the lower 50s across the
mountains of northern and western Pennsylvania, and mainly in the
mid 50s elsewhere.
Another murky day is expected across central PA today, as low lvl
(sfc-900 mb) easterly flow should keep nearly all of central Pa
under low stratus throughout the day. The morning/early afternoon
hours should see the greatest coverage of shower activity across
the western mtns, then a decreasing chance of showers from sw to
ne during the mid to late afternoon hours there.
06-08Z runs of the HRRR (and the mean of the 00Z-06Z NAM) shows a
nearly north- south ribbon 850 mb-based lifted indices in the -2
to -3C range forming from near KOLE to KUNV and KHGR in the 17-20z
period as the leading edge of cooling in the 700-500 mb layer
approaches from the west and the shield of thicker/high clouds
peels off to the east.
Although the near sfc layer will stay stable today, 925-850 mb
lifted indices will dip below zero across the region to the
southeast of the I-99/I-80 corridors this afternoon. This will
support a slight chc for a few elevated TSRA that will track
generally northward within some enhanced/fairly narrow bands of
showers. The western edge of this more focused area of showers and
isolated embedded TSRA should be near a KELZ to KSEG and KMDT/KLNS
LINE between 21-23Z.
Rainfall for the 12Z Sat-00Z Sun period will be a tenth or so in
many locations. places that see a few heavier showers and a brief
thunderstorm could see 0.25 to 0.50 inch of rain. The best chc for
these higher amounts would be across the region bounded by a line
from KELZ to KUNV...KMDT...KAVP...and KELM.
Blended model guidance (NBM) once again appears to warm and
unable to adequately handle the shallow/cool easterly llvl flow
and low clouds that will stay trapped in the ridge and valley
region and across the nrn mtns for much of the day.
EC and NAM guidance is 5-8 deg F cooler (and up to 10 deg F in a
few locations) than the most recent, 30/00Z and 12Z National
Blend of Models for most locations in our CWA today. Will keep
forecast max temps nudged closer to this cooler guidance. Highs
this afternoon will only make it to the upper 50s across the
mtns...and lower to mid 60s elsewhere.
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
Skies will stay mostly cloudy to cloudy tonight (mainly in the
form of stratus) as a near sfc easterly flow persists. Isolated
to scattered showers (and some patchy drizzle along the eastern
slopes and ridge tops will occur as one disturbance aloft exits
to the northeast of the region, and another upper 90-95 kt jetlet
moves into western PA early Sunday morning.
Rainfall amounts will be generally a few hundredths of an inch at
best in most places...with around one tenth possible in a few
locations. Similar low temps are anticipated tonight - in the
lower 50s across the northern and western high terrain, and mid to
upper 50s in the central and southern valleys.
.LONG TERM /SUNDAY THROUGH FRIDAY/...
Latest operational models track the persistent and slow-moving
cut-off low to near Detroit at 12z Sunday, before it finally
begins to turn east and gradually fills in as it gets picked up in
the longwave flow and tracks across NY state Monday.
The results on the forecast will be a continuation of showery
weather through the second half of the weekend, though with just
light amounts. Followed by a slight chance for showers across the
north early next week along with cold air advection filtering into
the region early next week.
Surface high pushing the cooler air our way slides off the New
England coast midweek, but persistent easterly flow feeding into
the Mid-Atlantic region should keep plenty of clouds around along
with at least a chance for light showers/drizzle across southern
half of CWA through midweek.
Latest on Hurricane Matthew in the 00z runs - Tremendous
differences have developed between the ominous GFS and the much
more benign forecast by the latest EC for the U.S. main-land.
The 00Z GFS brings a potent Matthew across the Western Bahamas
then has it paralleling the SE U.S. and Carolina coast late in
the week...before projecting it to get captured by a deepening
upper trough and accelerating north into Long Island next Sat/Sat
night. GEFS has roughly the same track, but as expected becomes
more diffuse through time with the location and intensity of the
storm`s center just off the East Coast.
The 30/12z operational ECMWF parked the storm over or just to the
north of the Bahamas for a prolonged period during the middle to
latter part of the upcoming week, which was a low confidence
The latest 01/00Z run of the EC now carries the hurricane well to
the northeast of the Bahamas Friday and on a steady course to the
Northeast toward Bermuda by the middle of next weekend. With such
drastic differences between the GFS/GEFS and the EC 5-7 days out,
we`ll continue to play the middle of the road and note just
scattered showers with the passage of a more definitive northern
stream shortwave and sfc cold front late next week or early next
Temperatures will be slightly below normal through the latter half
of the weekend, before shifting to slightly above normal by the
middle of next week...then possibly dipping back to near normal as
clouds (at least the mid and high variety) thicken-up to the NW of
.AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
Widespread IFR conditions will continue into tonight with
periods of -RA/BR/DZ. Gradual improvement to MVFR/VFR is
projected by later Sunday.
Sun...IFR trending to MVFR/VFR. Sct -shra.
Mon-Tue...Gradual improvement likely.