Area Forecast Discussion
Issued by NWS State College, PA

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000
FXUS61 KCTP 170541
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
141 AM EDT Thu Aug 17 2017

.SYNOPSIS...
Warm air will surge into our region Thursday ahead of an
approaching cold front. Showers and thunderstorms are likely
Thursday into Friday ahead of the front. Cooler drier should
improve our weekend weather. A ridge builds in early next week
and we should warm up before another northern stream cold front
triggers showers again and ushers in cooler drier around mid-
week.

&&

.NEAR TERM /UNTIL 8 AM THIS MORNING/...
GOES-16 advanced microphysics shows it is mostly clear over the
region to night. Deep clouds are well to west over IL-IN and
into western OH.

Clear skies and retreating surface high we should fade away fast
and clouds will come into the west toward morning. This will
produce some areas of patchy fog mainly near water bodies.

&&

.SHORT TERM /8 AM THIS MORNING THROUGH 6 PM FRIDAY/...
Used latest National Blend of Models in these grids minor tweaks
for timing of showers/thunderstorms. We rely on larger scale
models which over do light QPF in instability situations so
tempered the POPS down a tad.

But general trend is a good start to the day with increasing
chance of showers and thunderstorms west to east as the day goes
on.

Overall a warmer day with more humidity. Highs mainly in the 80s
with upper 70s in the northern and southwestern mountains.

Chance of rain and thunderstorms increases in the evening and
overnight hours as a deep cyclone moves into the western Great
Lakes. In the GEFS the 0000 to 1200 UTC Friday timeframe is the
wettest period. Strong southwesterly flow and above normal PW
implies good chance of convection and some areas could see
locally higher QPF amounts than depicted in the grids.

Due to high PW and clouds it will be a warm overnight.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
The GEFS and CMCEFS suggest our PW values drop during the day
Friday back to normal as the front is forecast to push to our
east. This means improving weather from morning to afternoon.
Lowering POPS over time.

We should remain relatively dry as the PW values stay near
normal until perhaps Tuesday. This said there are hints of a
weak wave and scattered showers perhaps Sunday.

Tuesday could be rather warm as there is a surge of above
normal 850 hPa temperatures and PW values above normal. Not
surprisingly the GEFS shows higher POPS Tuesday afternoon into
Wednesday with the wave and front.

We should enter the second half of the weak in a cooler and
drier air mass as currently forecast. And thus in the grids.

Bottom line in this period the NCEP guidance suggests low
probability of significant QPF.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
Some fog possible late.

06Z TAFS sent.

Earlier discussion below.

VFR continues late this evening and into the overnight hours
with high pressure and large-scale subsidence overhead. Fog
impacts are again expected to develop late and continue into
Thursday mid-morning - after which much of the day on Thursday
should be VFR.

Scattered showers will pop up Thursday afternoon in the west
and south and move northeastward. The coverage of these showers
before 18Z is too low to even mention PROB30s for any site in
this package. However, Thursday afternoon into Friday evening
hold a much more widespread chance of thunderstorm impacts as a
warm front lifts across the area and a cold front follows 24
hours later.

.OUTLOOK...

Thu night-Fri...SCT-NMRS TSRA impacts likely.

Sat-Mon...No sig wx.

&&

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

&&

$$
SYNOPSIS...Grumm
NEAR TERM...Grumm
SHORT TERM...Grumm
LONG TERM...Grumm
AVIATION...Martin/RXR



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