-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KCTP 160328
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1128 PM EDT Fri Sep 15 2017

.SYNOPSIS...
A large 500 hPa ridge with dominate our weather over the next
8 days. The only fly in the ointment is the trough and low
pressure associated with Jose. This circulation will come close
to the Mid-Atlantic region Monday into Tuesday before it
meanders to the East. Behind this trough a very strong 500 hPa
ridge with a closed 5880 m ridge is forecast to develop Friday
into Saturday.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
The last of the diurnally-driven showers have dissipated as of
02Z and the rest of the night should be dry.

A calm wind and clearing skies will promote valley fog
late tonight. SREF and downscaled NAM target the northwest
counties for the most extensive fog development with localized
visibilities near zero possible.

Relatively humid air mass over the region will keep temps from
falling much. Blend of latest guidance support mins from the
mid 50s northwest to the mid 60s southeast.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
Surface ridge over northwest Pa will result in limiting mixing
and may allow patchy valley fog to persist until late morning
over the northwest counties.

Model data continues to show anomalous 500mb ridge axis across
the eastern Grt Lks Saturday, while a weak trough lingers over
southeast Pa. This upper troughing and associated pocket of
cooler air aloft should result in isolated diurnally-driven
showers during the afternoon/early evening. Ensemble mean
925/850mb temps edge up slightly from Friday, so expect max
temps generally in the upper 70s to low 80s. The warm temps and
dewpoints in the 60s will make it fell almost like mid summer.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
For the most part a 500 hPa ridge will dominate our weather.
Our heights will drop as Jose approaches from the southeast and
there could be some showers on the northwestern side of the
storm and upper-level low which could affect southeastern areas.
A shift of the storm to the east will reduce our chance of
showers.

As Jose moves away heights will rise and this should further dry
us out. The GEFS forecasts a closed 5880 m ridge over us with
near +2 sigma above normal heights by Friday and Saturday next
weekend.

Some more detailed information:

The weak high at the surface should produce some patchy fog
over the region Saturday into Sunday. Some isolated shower
possible Sunday probably more convective QPF than any real
forcing mechanism.

Monday the flow is still weak and the PW is still low. But
clearly the NCEP and CMC guidance produces some isolated
convective precipitation so show slight to chance QPF in
northwest. Nothing to hang your rain drops on.

Tuesday several NCEP GEFS members bring rain into PA so we show
chance to slight chance POPS in southeast. This is consistent
with GEFS and CME EFS and other forecast offices. We are not
confident in this fringe rainfall on the edge of Jose. If only
knew the way for Jose.

Wednesday as GEFS and CMC EFS pull Jose off New England coast
our POPS drop. As this happens the heights rise fast and this
should lead to a period of dry and unseasonably warm weather to
end the week and start the weekend. Not sure why guidance in
blends showed 20-30 POPS under a ridge. I lowered them.

Big ridge means no big QPF events and definitely dry of Jose
finds his way....east. And very warm for late September.

&&

.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
Still quite a bit of clouds over portions of the area.

Thus backed off some on the duration of fog later on
for the 03Z TAF set.

More detail below.

Weak sfc and upper level low will depart slowly to the east
through this evening...maintaining VFR cumulus cloud deck
into this evening. Spotty light showers possible before 22z.
Winds will be very light and mainly from the NW/N.

Fairly widespread fog expected again west and central areas
with lcl IFR restrictions returns tonight, yielding on Sat to
variable VFR clouds - and poss an isolated shower mainly in the
SE.

.Outlook...

Sun...Patchy A.M. fog. Mainly dry with VFR conditions.
Perhaps an isolated afternoon shower.

Mon-Wed...Mainly dry with VFR conditions.
-- End Changed Discussion --

&&

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

&&

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