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FXUS61 KCTP 240135
Area Forecast Discussion
National Weather Service State College PA
935 PM EDT Tue May 23 2017
Weak system passing to our south today producing mainly clouds.
A very deep upper low will bring clouds across the region
Wednesday with rain developing overnight and into Thursday. This
deep low will produce cooler showery weather through Friday. As
this low lifts out Friday into Saturday a weak upper-level ridge
should provide several relatively nice days to start the
Memorial Day weekend. Alas another low may approach the region
on Memorial Day.
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Showers continue to straddle the Mason Dixon line late this
evening...with BKN-OVC skies covering all of central PA.
HRRR has been consistent in bringing a small batch of showers
northward into the West Central and Central Mountains later
tonight, and will carry slight chance pops for this thorugh the
pre dawn hours. Shower area becomes more fractured after
midnight and latest HRRR actually favors showers reaching the
Northwest mountains...but am not convinced of this just yet. Any
rain that does fall will be light...with only areas near the
Mason Dixon line potentially receiving up to a tenth of an inch.
Expect patchy fog across the southern half of PA as well.
Overnight lows will range generally through the 50s.
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
Tomorrow we should be mostly between systems. The clouds and
moisture from the wave to our southeast should be pulling away
overnight. And the clouds and rain from the deep 500 hPa low
will be heading our way from the west-southwest.
Most areas should have a pretty nice day, but once again on the
cloudier side of things. Kept POPS in the chance range in
southwest before 18 UTC and brought them up higher and into
central PA by 00 UTC.
Sometime from 2100 UTC Wed to about 0300 UTC it`s going to get
wet. But highest probability of rainfall in current guidance
will likely be on Thursday. New guidance might change this.
.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
As upper low drops into the TN Valley Wed night, surface low
develops over the Ohio Valley with a warm front extending
eastward across the mid atlantic states. Initial question will
be timing of onset of precip over CWA. Precip will be working
across W PA by early eve and will spread eastward as flow turns
from the SE around to the S, overspreading all of central PA by
the overnight hours. System slides through Thu into Thu night,
with a widespread rainfall around 0.75 inch.
On Friday, cool cyclonic flow on backside of departing cyclone
will maintain risk for showers. A lower-amplitude mid level flow
pattern will develop into the weekend with some ridging likely
at 500mb. Uncertainty regarding location and timing of shortwave
impulses rounding the ridge and effect of prior upstream
convection leaves plenty of question marks for Saturday - but
there is more agreement in area of max POPs over S OH/into WV
and SW PA in the afternoon.
NBM/ECE blend yielded the highest POPs for Sunday across
Central PA associated with cold front moving south/eastward
across the Great Lakes/Appalachians. A severe risk may accompany
the cold front but still to early for details. The large scale
pattern evolves into a broadly cyclonic regime into early next
week around an upper low between the Great Lakes and Hudson Bay.
This should keep the pattern unsettled with continued threat
for showers/Tstorms through Tuesday.
.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
Most of the flying area is under a blanket of high clouds. Far
SERN Pa is closer to an area of rain that is blossoming up over
the Mid Atlantic States and will continue to spread NE
Expect the mainly light rain to move into about the southern
half of the forecast area during the mid to late evening with
MVFR/IFR conditions developing. Northern areas will see just
spotty light showers and widespread sub VFR conditions are not
Conditions will improve slowly Wednesday morning with most areas
improving to VFR by mid day. MVFR could hang tough over the
Clouds will increase west to east as another system approaches
with rain and reduced conditions overnight Wednesday into
Thu...Rain/low cigs likely through at least midday.
Fri...Showers/MVFR cigs NW. Mainly VFR SE.
Sat...No sig wx expected.
Sun...Reduced conditions with scattered showers.