Area Forecast Discussion
Issued by NWS State College, PA-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KCTP 221008
Area Forecast Discussion
National Weather Service State College PA
608 AM EDT FRI JUL 22 2016
Pennsylvania will be on the northern edge of a subtropical ridge
into next week. An upper level disturbances and associated weak
cold front across the great lakes will move southeast and cross
Pennsylvania later this afternoon and tonight accompanied by
isolated to scattered, mainly afternoon and evening showers and
thunderstorms. Mostly sunny, very warm, and generally dry
conditions will follow for the upcoming weekend.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --Very warm temps aloft (around 8C at 700 mb) resided over the
state at 09Z, with even warmer mid-level temps noted further
upstream across the Upper Great Lakes.
Weak to moderate llvl positive theta-e advection will interact
with the cfront, and a rather potent 300 mb speed max of 80-90
kts headed SE from the glakes to support a growing area of tsra
over the next 3-4 hours.
These storms will continue to move southeast across the very warm
waters of Lake Erie and likely continue to strengthen as they move
into a favorable low-level environment of llvl moisture and .
After the early day activity fades across Northwest or Central
Penn, we should see a 3 or 4 hour period of generally hot but dry
weather. The fact that the storms will be moving steadily east
(within a mean 30-40 kt low-mid level jet, there should be little
threat of heavy rain/flooding problems. Ensembles point to an
increase in the PWATs ahead of the shortwave and associated
weakening cold front (that should make it to the the intersection
with a developing lee trough somewhere across north-central PA or
the Susq Valley).
HRRR pushes the bulk of the activity (that was currently lighting
up the north shore of Lake Erie) across the western southern tier
of New York this afternoon, then drives it ESE into N. Central Pa
and then the Poconos where SPC`s current day 1 outlook resides.
This fcast track of the convection appears to be a little too far
north...based on current regional WSR-88D Mosaic loop.
Elsewhere across the fcst area, SPC painted in a very broad area
of a MRGL Risk for severe weather from PA...west through the Ohio
Valley and covering the central and southern Miss Valley.
HRRR implies that much of the convection throughout the Central
MTNS and southern PA will dissipate during the 13-16Z timeframe
before firing up in a rather extensive line or lines from near
KAVP...to KSEG and KLBE and KPBZ.
0-4 km bulk shear will only be about 15-20 kts...and EHIs are
generally less that one inch. Therefore, the primary several
weather threat should come in the form of multi-cell clusters.
8h temps rising to near 20C should translate to max temps this
afternoon ranging from the m/US over the Alleghenies, to between
90 and 95F elsewhere. The heat, combined with rising dewpoints,
should result in widespread heat indices in the 90s.
-- End Changed Discussion --
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/...
-- Changed Discussion --After a few scattered showers and thunderstorms...mainly early
tonight...cooler and noticeably drier air will filter southward
into the region.
Lingering areas of stratocu and alto cu and a light westerly
breeze will keep min temps mainly in the 60s...to lower 70s in the
-- End Changed Discussion --
.LONG TERM /SATURDAY THROUGH THURSDAY/...
Big story in the extended fcst is expected heat wave lasting into
early next week, as axis of subtropical ridge briefly shifts from
the plains to the northeast conus. Anomalous upper lvl ridging
building over PA should bring hot and mainly dry wx this weekend,
as warm temps aloft suppress convection. Next chance of shra/tsra
for most of the area comes Monday ahead of shortwave working
across the Great Lakes. However, any rainfall Monday is likely to
do little to stem the dry pattern we have been in. Latest GEFS
mean qpf is up to a half an inch at most.
12Z ECENS/NAEFS mean 8h temps are near 22C Saturday through
Monday, indicating the potential of several days in a row with
highs in the 90s in the valleys. The hottest temps look to be on
Saturday as latest GEFS gives high temperature anomalies in the
+4 standard deviation and have slightly backed off on Sunday. Have
adjusted Max temperatures accordingly. Heat indices around 100F
appear possible by Mon across the Susq Valley, as higher dewpoints
are advected into the area. Overnight lows are also a concern as
the area doesn`t cool off at night through the weekend with
Southern PA lows in the 70s with highest readings Monday morning.
Some modest cooling appears likely by Tue/Wed of next week behind
weak cold front. However, temps still likely to remain somewhat
abv normal within a generally zonal flow.
.AVIATION /10Z FRIDAY THROUGH TUESDAY/...
VFR conditions should prevail through the majority of the period.
Area of showers/TS developing northwest of Lake Erie may reach the
BFD terminal area 12-15Z. Isolated to widely scattered thunderstorms
remain possible across the entire airspace this afternoon through
the early evening. Limited coverage/low confidence will preclude
TS mention for now and will reassess with the full suite of near
term meso guidance by the 12z scheduled issuance. The greatest
risk for strong to severe TS appears to be across the northeast
airspace in ZNY sector.
SAT-SUN...Early morning fog possible...otherwise no sig wx.
MON-TUE...Restrictions possible with a chance of SHRA/TSRA.