Area Forecast Discussion
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FXUS61 KCTP 261730
Area Forecast Discussion
National Weather Service State College PA
130 PM EDT Mon Sep 26 2016
A cold front will move through quickly later this afternoon and
early tonight. After a dry day or two, the forecast becomes rather
wet with a cut off upper low .
.NEAR TERM /THROUGH TONIGHT/...
Considerably amount of clouds stuck in the ridge-valley system of
central Pennsylvania this morning. Sunny to the west and sunny to
the east and here I am, stuck in the clouds with you. A nice early
season cold air damming (CAD) event. For the enthusiasts out
there, the 1000 and 925 theta-e contour show this quite nicely
this AM as does the HRRR/RAP dew point fields. All our clouds are
in the gradient between the warmer air to our southwest and the
cooler drier air to our northeast.
I used the HRRR to texturize the clouds a bit and to better time
the frontal rain headed our way. The coarse GFS/GEFS have too
much light rain too fast. The real front and frontal clouds are
well back in Ohio. Most of the eastern half of central PA should
remain a rain free zone until later this evening.
Showers will arrive in the west later this afternoon and the HRRR
implies some enhanced echoes suggesting some modestly organized
thunderstorms along the line of showers. But the weaken in central
PA due to the CAD event. Pretty stable to the north and east.
The HRRR has chance showers with a narrow cold frontal rainband by
18Z and central PA around 21Z reaching Harrisburg an hour to two
either side of 00Z. The HRRR simulates what looks like a narrow
cold frontal rainband which I timed above. The HRRR also shows
the weak evolution of a wideband back in the cold air later this
evening in central PA. This implies two shots of enhanced
rainfall. The wide cold frontal band does not clear
Harrisburg/York/Lancaster until after midnight as it grows in size
The GEFS too shows similar timing of maximum rainfall periods just
to diffuse. It clears out our light rain by 0600 UTC tonight.
The air behind the front should actual be quite dry and conditions
will improve over night west to east. Precipitable water values
drop about -1sigma below normal overnight behind the front.
.SHORT TERM /TUESDAY/...
All the rain should be gone well before sunrise and our PW values
should be well below normal. Some strong winds to mix down so
should be a breezy day and on the cool side of normal along with
very dry air. Thus it should be a pleasantly cool early autumn
There is not real anticyclone behind this system. But the winds
should diminish as we stabilize in the late afternoon and early
.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Should be relatively quiet weather Tuesday night into Wednesday.
But the cyclone and developing cut-off to our west and the
boundary along the front to our southeast will impact our weather
PoPs should creep up in southeast Wednesday due to the frontal
boundary. The deep cut-off low to our west will increase shower
risk in western PA Wednesday afternoon. And by Thursday the big
cut-off will likely bring us very cool and showery weather for a
Previous: The mid week period will bring the large upper level
low through the Great Lakes and down into the Ohio Valley. The low
will slowly progress eastward with model PWATS increasing through
the latter half of the week. Couple this with the Southwesterly
flow and will allow for an increase of POPS Through the second
half of the week and into the weekend. This will make the forecast
a little milder at night and slightly cooler in the day, but very
nearly normal. Have kept up with the overall trend of increasing
POPs for the latter half of the week and into the weekend. The
upper low is currently progged to lift northeast, but probably not
until then end of the long term period.
.AVIATION /18Z MONDAY THROUGH SATURDAY/...
Updated the TAFS with the latest guidance and tweaked shower
timing to the 16Z HRRR. VFR will dominate the rest of today. Someareas
of MVFR in west as the front is entering westernmost PA this
afternoon. There are considerable areas strong surface winds which
could affect approaches.
This front will bring a 1-3 hour shot at showers and isolated
thunderstorms in the northwestern areas and mainly a 1-3 hour
shot at showers in the central and east later this evening and
early tonight. Tried to time this frontal passage over the next
12-15 hours. Expect 1 to 6 hours of MVFR and areas IFR with this
Very dry air behind the front with only brief period of IFR/MVFR
as the system moves to the east. Then conditions rapidly improve.
VFR Tuesday though a breezy day.
Wed should be the last good VFR day then more showery and cloudy
conditions later in the week into the weekend suggest mix MVFR/VFR
and locally VFR.
Tue...No sig wx expected.
Wed...Showers/cig reductions possible late.
Thu-Fri...Sct showers/cig reductions possible, esp w mountains.