Area Forecast Discussion
Issued by NWS State College, PA

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957
FXUS61 KCTP 180547
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
147 AM EDT Fri Aug 18 2017

.SYNOPSIS...
A cold front will move through the region Friday triggering
showers and thunderstorms. The cooler air will be replaced by
warmer air Monday into 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 /UNTIL 7 AM THIS MORNING/...
There were a few thunderstorms were over south-central
Pennsylvania at 930 PM. Some showers were present over northern
and northwestern Pennsylvania.

The HRRR pushes the area of shower to the west through the
region by 4 AM. Rainfall amounts are generally light. Some hints
in northwestern PA of some potentially stronger cells with
rainfall potential of an inch in these stronger cells, should
they develop.

Many areas, especially in the southeast should remain rainfree
overnight though patchy fog is possible.

&&

.SHORT TERM /7 AM THIS MORNING THROUGH 6 PM SATURDAY/...
The HRRR goes to about 17Z and it shows a weak line of showers
and thunderstorms across our southwestern counties northeast
toward Tioga county. General concept is showers developing
around 15-17Z Friday.

The HRRR shows CAPE over 2400JKG-1 east of these showers and
other NCEP models show over 1800JKG-1 of CAPE to the east. Thus
have higher POPS in central to southeastern PA in the afternoon
hours.

Models indicated the potential for some strong to severe
thunderstorms Friday afternoon and the potential for some
locally heavy rainfall. Most models show mainly 0.25 to 1.00
inch of QPF but stronger cells could produce higher amounts.

Most guidance shows the cooler drier air improving conditions in
western PA in the late morning and early afternoon. The front
should clear our southeastern counties in the 22Z to 03Z
timeframe Friday evening.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Models imply a weak wave could trigger some light showers on
Saturday evening. Sunday into Tuesday looks very dry. The next
chance for widespread rain would likely be around Wednesday and
possibly into Thursday as short-wave and cold front move into
the region.

At this time Wednesday has the higher probability of QPF then it
dries out Thursday into Friday. The PW forecasts show low PW
over the region Saturday to Tuesday then a surge of higher PW
air Wednesday ahead of the front. Then the PW falls Thursday
into Friday to below normal values.

Temperature wise, the cool air should be replaced by warmer air
by Monday afternoon and Tuesday should be even warmer still. The
850 hPa temperatures go above normal Monday evening and peak in
the 16-19C range Tuesday afternoon. Tuesday could be quite hot.

Good news is the 850 hPa temperatures fall Wednesday into
Friday. Most guidance shows below normal 850 hPa temperatures by
Friday with below normal PW values. The week as currently
forecast should end on a cool dry note (like D sharp?).

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
A band of showers and a few thunderstorms is pushing across
the area as of midnight.

Some rotation on cell heading toward IPT. Strong southeast
flow off the mountain south of IPT for a few more hours.

Another area of showers and storms over far southwest PA.
Expect this area to slowly work to the northeast and linger
into at least into the mid to late morning hours.

Skies should try to clear later today, but the cold front will
be well to the west. Main concern is the very high dewpoints
in place, one of the few times this summer. Main difference
this event is that the low level winds shift to the south
and southwest, unlike recent events, that seem to occur at
the end of the week this season. For now, will use VCSH for
the most part. Potential is there for storms with heavy rain
and strong winds.

Weekend not looking bad for a change.

.OUTLOOK...

Sat-Mon...No sig wx.

Tue...SHRA/TSRA poss.

&&

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

&&

$$
SYNOPSIS...Grumm
NEAR TERM...Grumm
SHORT TERM...Grumm
LONG TERM...Grumm/Lambert
AVIATION...Grumm/Fitzgerald/Martin



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