Area Forecast Discussion
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FXUS61 KCTP 291151
Area Forecast Discussion
National Weather Service State College PA
751 AM EDT Thu Sep 29 2016
A widespread moderate to locally heavy rain event will continue
through tonight. Minor flooding impacts are likely across the
southern half of central PA. Unsettled weather with occasional
lighter rain showers will persist into the weekend with a gradual
drying trend by early next week.
.NEAR TERM /THROUGH TONIGHT/...
7AM: Rain event thus far has been pretty orderly/soaking with
some 2+ inch amounts observed over far south-central PA. No
changes with this update. -MS
The 29/00z guidance remained in good agreement with the deep upper
low that is forecast to settle further south from southern IN into
central KY today before lifting gradually back to the north after
00-06z Friday. The ongoing rain shield is being handled pretty well
by the HI-RES guidance. The highest rain amounts in the last ~6
hours generally range from 0.75 to 1.5 inches across Bedford to
Radar trends and latest HRRR suggest the north-south heavy rain
band developing near the I-95 corridor from DCA to near RIC may
focus into the Lower Susquehanna Valley through mid morning, as
deep moisture from the Atlantic is driven inland by anomalous ESE
LLJ and intersects a frontal boundary/convergence axis. This
scenario is also hinted at by the HIRES NCAR ensemble mean QPF
which shows a stripe of 2+ inch amounts.
The strength of the upslope flow and high PW transport along with
some elevated instability will maintain a favorable environment
for heavy rain/efficient rainfall processes, while increasingly
diffluent flow aloft supports some training bands. As the upper
low settles a little further south, backing flow should shift the
heavy rain focus back toward the upslope regions of the Laurel
Highlands this afternoon into tonight.
Overall did not change QPF amounts very much with 50/50 blend of
the latest WPC guidance with the previous forecast. This should
mitigate some of the detail differences between individual model
QPF. Still calling for widespread 2-4" over the flood watch area
with locally 4-6" most likely across the east-facing slopes and
highest terrain. WPC QPF was based in large part on an ensemble of
HIRES guidance. What is a little concerning is the mean 24hr QPF
from the NCAR ensemble which shows the potential for 6+ inches.
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.
.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
The upper low continues to double back to MI on Friday before
slowly tracking eastward into the Lower Great Lakes over the
weekend. 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.
.LONG TERM /MONDAY THROUGH WEDNESDAY/...
The trend for early next week is toward dry weather as the
stubborn upper low is finally is kicked to the northeast by
upstream amplifying trough over the Nation`s mid section. High
pressure should regain control of the large scale pattern. FWIW
the 29/00z GFS is much faster vs. the ECMWF with the projected
path of TC Matthew, with the system nearing the NC coast by
.AVIATION /12Z THURSDAY THROUGH MONDAY/...
An increasingly moist easterly flow will will produce low cigs
and rain across central Pa today. Model soundings and latest SREF
output support predominantly IFR cigs through this evening at the
higher terrain airfields, including KBFD, KUNV, KAOO and KJST. At
the lower elevation airfields, predominantly MVFR cigs are
expected today at KIPT, KMDT and KLNS. However, periodic IFR is
likely this morning associated with bouts of heavier rain.
Fri-Sat...Low cigs/showers likely, mainly w mtns.
Sun...AM low cigs possible.
Mon...Showers/cig reductions possible at KBFD.
Flood Watch through Friday morning for PAZ024>028-033>036-056-