Area Forecast Discussion
Issued by NWS State College, PA-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KCTP 290050
Area Forecast Discussion
National Weather Service State College PA
850 PM EDT Wed Sep 28 2016
A multi-day heavy rain event will commence tonight and continue
through Thursday night and Friday. Minor flooding impacts are
likely across the southern half of central PA...but impacts should
be lessened to some extent by dry antecedent conditions. Unsettled
weather with occasional lighter rain showers will persist into the
weekend with a gradual drying trend by early next week.
.NEAR TERM /UNTIL 7 AM THURSDAY MORNING/...
Lone thunderstorm moving north thru the SC counties. So far,
precip amounts have been as expected, with a gradual building of
the moisture. Clouds have filled in across most of the west as
well. Minor tweaks here and there to aftn pkg mainly to add just a
mention of T to the wx grids for the south.
Increasing southeast flow aiding expansion of lower clouds from
the Mason Dixon line northward into the Laurel Highlands and parts
of the South Central and Central mountains and Ridge and Valley
region at mid afternoon. Deep easterly flow with long over water
fetch from the Western Atlantic is pushing low clouds westward
from the Hudson River Valley into eastern PA as well.
Showers are breaking out over the ridge and valley region and
lower Susq this afternoon...and expect them to become more
persistent and heavy as we get into the evening hours...as per
Clouds will continue to increase from south to north throughout
the mid and late afternoon as southeast flow increases and
boundary layer moisture deepens. Model guidance still shows the
main surge in rain coverage and intensity later tonight into
Thursday which corresponds with arrival of stronger dynamical
forcing and strengthening E-SE upslope low level flow. Showers
with locally heavy banded and orographics will increase by late
evening and overnight across the southern third to half of central
.SHORT TERM /7 AM THURSDAY MORNING THROUGH FRIDAY/...
Heavy rain event is expected to be ongoing over south-central PA
on Thursday. An enhanced convergence axis/frontal zone is progged
to develop on the east side of an upper low meandering over the
OH/TN Valley, tapping into deep moisture/high PW air off the
Atlantic Gulf Stream via anomalous east/southeast low level jet.
The heavy rain axis is progged to gradually pivot to the southwest
with time oriented within moderate excessive rain outlook area
from southwest PA near the Laurel Highlands southeast into
Northern VA/D.C. area. The strength of the upslope flow and high
PW transport along with some elevated instability should provide
an environment for efficient rainfall processes.
WPC QPF nudge employed this afternoon but overall staying the
course from previous forecasts...despite a downtick in some
deterministic solutions in the 12z cycle. Dry antecedent
conditions may limit more significant flooding/runoff issues.
Still expect minor flooding to result from long duration
continuingthroughout Thursday. event...and am maintaining Areal
Flood Watch for Laurel Highlands, South Central Mountains and
southern portions of the Central Mountains for late tonight
through Friday morning. Will continue to highlight potential flood
risk in HWO elsewhere...but heaviest rain should fall across the
southern half of the area.
The upper low is fcst to drift back to the west/NW into the OH
Valley on Friday before slowly moving to the ENE across the Lower
Great Lakes through the weekend. We should continue to see periods
of showers on Friday but rainfall amounts will be much lower and
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
The upper level low will continue to slowly move through the
Eastern Great Lakes region and into Southern Canada which should
pull the moisture to the north. Some lingering showers should
continue through Eastern PA Saturday afternoon. There is some
disparity on the timing of the exit of this low and whether or
not it opens up into a wave. The model guidance still suggests
unsettled conditions over the weekend with a gradual decrease in
the chance for showers by Sunday. Temps still holding close to
seasonal normals as we turn the calendar to October.
.AVIATION /01Z THURSDAY THROUGH MONDAY/...
-- Changed Discussion --Increasing deep layer, south to southeasterly flow above a
relatively cool/easterly flow at the surface will lead to
gradually deteriorating flying conditions and increasing areal
coverage of rain overnight into Thursday.
Reductions in the form of IFR expand northward tonight and impact
all sites Thursday. Poor flying conditions will last for much of
the time through at least Friday.
Thu-Fri...Widespread showers/cig reductions.
Sat-Sun...Reductions possible both days with some showers likely,
especially on Saturday.
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Flood Watch from 2 AM EDT Thursday through Friday morning for