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FXUS61 KCTP 250927
Area Forecast Discussion
National Weather Service State College PA
527 AM EDT THU AUG 25 2016
A seasonally warm and humid late-summer weather pattern will
continue across Central Pennsylvania into next week. Scattered
thunderstorms with strong wind gusts are possible in the Northwest
Alleghenies later this afternoon into the evening.
Line of showers associated with pre-frontal trough will move
across the Alleghenies early this morning before weakening to the
east of RT 219/I-99. Followed the recently upgraded HRRR very
closely through late morning which seemed to have a good handle on
the current/evolving radar trends. Used a blend of convective-
allowing models (CAMs) for the remainder of the near term period
which resulted in max POPs over the NW Alleghenies during the late
afternoon into early evening. This area is included in the MRGL
severe Tstom risk outlook from SPC. In the absence of large-scale
forcing for synoptic lift/neutral- to-weak height rises, diurnal
heating - which may be delayed due to cloud cover early in the day
- and small scale shortwave impulses will play a key role in
renewed convective development. This of course adds some degree of
uncertainty into the forecast. Assuming this occurs as is
generally depicted by a consensus of CAM guidance, a few strong to
locally damaging wind gusts will be possible mainly over Northwest
PA within corridor of high PW and 30-40kt mid-level flow. Expect
any storms to weaken after dark given loss of instability, with
decreasing coverage into the overnight hours.
There is increasing confidence in a dry Friday, as all models now
push dying cold front southeast of the region by 12Z Sat. Main
effect of fropa will be to lower humidity, as GEFS 8h temps remain
above normal behind front, likely supporting max temps from the
low 80s across the nw mtns, to around 90F in the Susq Valley.
Model soundings suggest Friday could begin mcldy over the
Alleghenies, but any post-frontal stratocu should mix out to
msunny skies everywhere by aftn.
Sfc high will build over the region Friday night, resulting in a
fair and mild night. Will have to watch for the possibility of
patchy valley fog over the northern mtns late.
Center of subtropical ridge over the southeast conus is progged
by all models to migrate northeast to the Mid Atlantic by this
weekend. Lg scale subsidence and warm temps aloft assoc with this
feature should translate to hot and humid conds with little
chance of rain across most of Central Pa. However, a shortwave
tracking across southern Ontario could trigger sct late day
shra/tsra on Sunday across northwest Pa.
00Z NAEFS and ECENS both strongly favor a continuation of well
abv normal temps into next week with mean 8h temps still btwn
18-20C. Weakening upper ridge is progged by mdls to slip southward
a bit, placing Pa within a more favorable regime for diurnal
convection on northern edge of upper ridge within plume of
anomalous PWATS. High humidity and warm nights appear likely into
next week, esp across southern Pa, where anomalous PWATs on the
order of +1SD indicated in the 00Z GEFS.
Line of showers/storms over eastern OH should gradually weaken as
it shifts ewd across the western-central airspace between 09-12z.
Confidence is low in the band holding together into ZNY sector.
Agree with guidance bringing a short period of low MVFR to IFR
cigs into KBFD/KJST behind the line given moist low level flow
ascending the higher terrain. Conditions trend to VFR into mid-day
with focus shifting to potential thunderstorm impacts for the
afternoon/evening. Will wait to examine the latest CAM guidance
before adding mention of thunder with the 25/12z scheduled TAFs.
Scattered showers remain possible tonight with some restrictions
likely heading into Friday morning.
Fri...A.M. restrictions possible; becoming VFR. Isold thunderstorms
possible southern 1/4 airspace in the afternoon.
Sat...Patchy A.M. fog. Otherwise no sig wx expected.
Sun...Isold thunderstorms possible western 1/3 airspace in the
Mon...Isold-sct thunderstorms possible.
NEAR TERM...Fitzgerald/Steinbugl
SHORT TERM...Fitzgerald
LONG TERM...Fitzgerald

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