Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 200315
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1115 PM EDT Wed Jul 19 2017

.SYNOPSIS...
Pennsylvania will be on the periphery of the subtropical ridge
through the weekend. Temperatures will be above normal and there
is the risk of an MCS in the ring-of-fire moisture plume. The
heights are forecast to fall over the weekend into early next
week suggesting cooler, dry weather next week.

&&

.NEAR TERM /UNTIL 8 AM THURSDAY MORNING/...
Overnight weather problem will be developing fog again in moist
airmass and clearing skies.

&&

.SHORT TERM /8 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
Fog burns off so we shall have some haze Thursday. Most
guidance shows more instability and showers developing to our
northwest Thursday which will drift and trigger showers near or
in our northwestern counties in the afternoon and evening on
Thursday. Cannot rule out a few stronger storms in northwest
Pennsylvania Thursday afternoon.

Chance rain best in northwest and less than 10 percent in
southeast.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
The latest thinking is that upstream convective activity should
evolve east-southeast across the Lower Great Lakes during the
afternoon and reach PA by late Thursday afternoon into Thursday
night. The details remain somewhat unclear at this time given
the prospects of new storm development in advance of initial
/Day 1/ MCS and potential for additional storms out ahead of
outflow boundary or cold front. Global model QPF may be too far
north with QPF max which is a typical bias in MCS/ring of fire
patterns. The slight risk was adjusted southward to align better
with projected MCS movement and axis of best instability.
Showers and storms should weaken and dissipate late Thu night
into Friday morning. Model data shows large scale subsidence
over the area during the day on Friday with convective activity
re-focusing over the Midwest/Great Lakes Friday night and
propagating east-southeast toward central PA by Saturday
morning.

The Day 3 MRGL risk extends into west-central PA on the
eastern extent of upstream organized convective zone. Over the
weekend, pcpn pattern looks to reach a relative peak with max
POPs based on multi-model blend. Exact timing and location of
pcpn will depend on details not well resolved until the very
short term time frame. Therefore the later periods will keep a
40-60 percent POP given lack of confidence in highlighting any
specific areas/timeframe with concentrated pcpn potential.

Medium range models generally agree that a continued/gradual
weakening and east-southeast shift of the persistent central
U.S. upper ridge can be expected with time, as shortwave
troughing shifts slowly southeast out of the Canadian Prairie
across the northeast quarter of the country by early next week.

The other concern is for a several-day period of hot/humid
conditions punctuated across the Lower Susquehanna Valley with
blended guidance showing 2-3 days of 90+F max temps with max
heat index potential approaching 100F. The heat risk remains in
the HWO. A heat advisory may be needed for at least 1 day based
on NDFD max HI and WPC D3-7 HI probs. The hot temperatures
should be eroded from the NW with time, as the frontal boundary
gradually sinks to the south in response to mean troughing
developing late in the period. Above average temperatures (+5-10
degree max T departures) should trend toward mid to late July
climo numbers by next Tue-Wed.

&&

.AVIATION /02Z THURSDAY THROUGH MONDAY/...
Another round of showers and thunderstorms moving through south
this evening. All convection is over for the evening and VFR is
currently dominating. with high minimum temperatures and high
dewpoints, another round of patchy fog/mist and low stratocu is
possible tonight into tomorrow. Best chances will be along the
south where it rained, especially MDT, IPT, AOO and JST.
 Expect any restrictions to improve between 12z to 14Z.
 Tomorrow will bring an increased chance showers and
thunderstorms through NW PA Thursday afternoon with better
chance tomorrow night in the central and southeastern areas


.OUTLOOK...

Thu...AM valley fog. Cig restrictions poss NW. TSRA PSBL NW Thu
aft, scattered TSRA central Mtns Thu eve.

Fri...AM valley fog/cig restrictions likely NW half. Isolated
TSRA.

Sat...AM valley fog poss. TSRA likely.

Sun...AM valley fog poss. TSRA likely north/scattered south.

&&

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

&&

$$
SYNOPSIS...Gartner
NEAR TERM...Gartner
SHORT TERM...Grumm/Gartner
LONG TERM...Steinbugl
AVIATION...Grumm/Ceru


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