Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 181901
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
301 PM EDT Fri Aug 18 2017

.SYNOPSIS...
A cold front will move through late today. An upper trough will
move across the area on Saturday. Temperatures will stay above
normal but rise even higher each day through Tuesday as a ridge
builds aloft. Another cold front should trigger showers around
mid-week and the week should end on a cooler note.

&&

.NEAR TERM /THROUGH TONIGHT/...
Numerous SHRA and a few TSRA now cover much of the SE. All is on
track with the fcst. New SVR watch just issued to cover severe
threat of mainly wind damage, but some spinners/right-movers are
already occurring and there is a risk for brief tornadoes with
such low LCLs and shear sufficient to make mini-supercells. Not
much ltg right now due to warm temps aloft. Much of the area
will be either worked-over (stabilized) or just plain out of
the threat area withing the next 2-3 hours.

Secondary line of showers over the NW is likely the front, but
some additional development along that line or between the
current area of storms and that line is possible. These storms
sould not be as active/dangerous as the first area. A tertiary
line of showers/storms is then possible over the nrn mtns this
evening, but without much instability and CAPE left, these
should not be severe. Clearing is

Low clouds could form along the western highlands after sunset.
Some fog is possible - mainly in places that are getting the
heavy rain and have little time to dry out but also clear out
well. That would be the SE counties. Dewpoints will dip into the
m60s in the NW shortly and down to around 60F tonight. The m70
dewpoints in the SE will likely only dip to the u60s for the
overnight. Can`t see temps going below those numbers.

&&

.SHORT TERM /SATURDAY/...
The high pressure moving in finally clears everyone out in the
morning. Any low clouds in the NW will dissipate nicely with the
sunshine. The trouble there is that the lingering moisture, the
passage of the upper trough and enhancement from a potent short
wave coming around the base will meet up at peak heating. These
factors and the wind field will generate multiple showers in the
NW half of the area in the aftn. Some of these will make some
good gusts - and some could get severe. A little small hail is
also possible with colder air aloft than today. SPC does have
that area in a MRGL risk for severe wx. The showers/storms will
struggle to get past the Allegheny Front (roughly IPT-UNV- AOO
line). Max temps will be right near normals.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
After the shortwave moves through the area by later Saturday,
heights aloft are forecast to rise and become quasi-zonal.
Sunday into Tuesday looks warm and dry, with Tuesday even ending
up hot over most of the area. A new shortwave moving through
SRN Canada will an bring an increasing chance for rain, possibly
as early as Tuesday afternoon over western sections of the
forecast area.

There are differences in timing of the rain with the ECMWF
suggesting it holds off until Tuesday night. Blended MOS POPs
show a small chance of showers moving into western sections
Tuesday afternoon, but the highest POPs are reserved for the
overnight.

Cyclonic flow aloft will then dominate the flow pattern through
Thursday. The cool air aloft will help trigger a few mainly
diurnal showers Wednesday and Thursday. The showers will tend to
favor northern and western higher elevations. Temperatures will
be significantly cooler for the second half of the week.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
Storms all over the radar scope at 19z SE of UNV-IPT-AOO. Just a
spot of showers in the N east of BFD. That spot is probably
along the real cold front as there are lower dewpoints
immediately to the west of it. Additional storms are possible
in the west and central counties late this aftn, but most
locations will remain dry and VFR.

A final push of drier air will move through this evening and
early tonight. Thus, a few shra are possible in BFD between 23z
and 02z - but the other terminals should stay dry this evening
and tonight. Fog is possible for most of the area tonight, but
more so in the SE where it has rained and had clearing, but
little time to dry. Lower clouds should form over the NW mtns
tonight, but these should stop around the old AOO-UNV-IPT line.

An upper level trough and rather strong forcing passing
directly overhead in the cooler air aloft could make sct
shra/tsra across the northern third/half of PA on Sat aftn.

Much drier air will make for a mainly-VFR Sun-Mon with only
valley fog in the AM a potential issue.

.OUTLOOK...

Mon...No sig wx.

Tue-Wed...SHRA/TSRA poss.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...Dangelo
NEAR TERM...Dangelo
SHORT TERM...Dangelo
LONG TERM...La Corte
AVIATION...Dangelo


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