Area Forecast Discussion
Issued by NWS State College, PA-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KCTP 300213
Area Forecast Discussion
National Weather Service State College PA
1013 PM EDT Thu Sep 29 2016
Showery conditions will prevail overnight. Any flooding would be
localized and minor with little in the way of impacts. Unsettled
weather with occasional lighter rain showers will persist into the
weekend with a gradual drying trend by early next week.
.NEAR TERM /UNTIL 8 AM FRIDAY MORNING/...
-- Changed Discussion --Still a neat little box around 95 pct of central PA where no
radar echoes exist. It is drizzly at may locations, but that stuff
is too low (and the droplets too tiny for most 10cm radars) to
pick up. A slight increase in radar echoes is starting to move in
from the south and precip in DE also sliding just a little to the
west of north. HRRR and RAP doing well with the first couple of
hours in the past few runs, so higher than normal confidence
exists that they will do well with the rest of the night. 00Z NAM
arriving and continues to make heavier rain than other mdls. The
placement of the heavier rain is mainly to the east of the Susq
and is an area where generally less rainfall occurred. That area
has also had a decent break of time since any real rain has
occurred. Grid work with this update was mainly to dip the POPs to
=<20pct in the north for the next few hrs. However, the guidance
is big on developing the precip associated with a wave moving up
the MidAtlantic coast. This area would then blossom as it enters
eastern PA and make the heaviest rain in the east for a few hours
either side of sunrise while lifting north. The northern mtns
should then have their best shot at some rain during the daytime
Rainfall down to nil at the moment with central PA in the dry slot
between a higher plume of moisture to the east and another to the
west. Newest progs yield only light to what might be considered
modest amounts of rainfall through sunrise. 18Z NAM seems like a
high-end outlier on QPF amount - and only for a small area. Stream
response has been very little if anything on the medium to larger
streams. Even NAM amounts and placement will not cause widespread
flooding problems. The ground and still-growing vegetation are
gladly soaking it up. Have decided to chop the rest of the Flood
Watch off. Have adjusted POPs in the very near term to account for
the dry slot and GFS/HRRR/RAP evolution of the rain for the rest
of the night.
2.5 to 3.5 inch amounts feel across southern tier overnight
through midday...with higher amounts likely on the east facing
slopes occurred across the southern tier. Flooding threat
remains...albeit low...with upslope areas susceptible to any
persistent upslope or training convective showers over the next
18 hours which could add another 1 to as much as 2 inches in some
Dry slot over western PA with high cloud covering eastern brought
transition to low topped open cellular activity propagating from
southeast to northwest today. Thus a more showery regime took over
with times of little or no rainfall and other times with brief
moderate to heavy rates accumulating a few tenths of an inch at
Moderate PW transport along with some elevated instability will
maintain a favorable environment for mdt-heavy rain/efficient
rainfall processes through this evening, while increasingly
diffluent flow aloft supports some training bands in addition to
the trend to low topped open cellular character. In
fact...training bands have organized over nrn VA/MD at mid
afternoon and are moving into the Laurels and South Central
Mountains...as anticipated earlier.
Still expecting storm totals of 2-4" over the remaining flood
watch area with locally 5"+ possible along the east-facing slopes
and highest terrain. Very dry antecedent conditions resulting in
3-6hr FFG values of 4+ inches along with below normal stream flows
should help to mitigate flooding to some extent, however if the
higher end amounts are realized flooding impacts/runoff issues
could become more serious.
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.SHORT TERM /8 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
The Large low will be quasi stationary and will continue to stream
moisture into Southwestern PA through tomorrow. Strong E-SE LLJ
and above normal PW along with associated forcing on
east/southeast side of upper low favors scattered to numerous
lighter rain showers through the period. The mid range models are
keying in on a mid level short wave trough that forms to the east
of the low and should increase rainfall rates and amounts through
Central PA as it is coupled with the LLJ and the PWATS.
.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
The upper level low will continue to spin slowly northward into MI
and continue on into Southern Canada. The low will slowly be
pulled into the upper level flow and cold air advection will
filter into the region early into next week. The final vestiges
of the low that has dominated our weather pattern this week will
finally lift and move off coast by mid next week by the upstream
amplifying trough over the central CONUS. High pressure should
regain control of the large scale pattern. The 12Z GFS comes more
into alignment with the EC however the EC continues the path of
the TC Matthew much slower and keeps it off the coast of Florida,
where the GFS brings the projected path up the Atlantic coast and
has the system nearing the NC coast by Thursday morning.
Temperatures will be slightly below normal through the weekend,
before shifting to slightly above normal by the middle of next
.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
Low clouds and areas of light rain, drizzle, and fog will
linger across the area, given strong easterly flow of moisture
off the ocean. MVFR to LIFR conditions will prevail.
Not much change expected overnight or on Friday.
Sat...Low cigs/showers likely, mainly w mtns.
Sun...AM low cigs possible.
Mon...Showers/cig reductions possible at KBFD.