Area Forecast Discussion
Issued by NWS State College, PA

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493
FXUS61 KCTP 240044
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
844 PM EDT Sun Jul 23 2017

.SYNOPSIS...
A frontal boundary will remain in the vicinity of Pennsylvania
through Monday...touching off scattered to numerous showers and
strong thunderstorms...some with heavy downpours through late
tonight and early Monday morning. Another round of showers and
thunderstorms is expected on Monday before high pressure builds
into the region by the middle of next week. A cold front will
likely push southeast in the state toward the end of next week.

&&

.NEAR TERM /UNTIL 7 AM MONDAY MORNING/...
Heaviest convection waning over the east, but moisture remains
very high. Flooding in Middletown is pretty bad at this hour,
but may start to improve shortly without current rainfall.
However.......
Convection over the N is along a wind shift boundary and most is
sliding to the south. Convection over SWrn PA is looking like it
will collide with that boundary. Most CAMs do pump up convection
over the central counties - and the cells just to the S of UNV
and IPT are evidence that it is still unstable in some small
degree. Thus, will have to continue to watch for flash flooding.
The wettest areas and the most likely areas to see heavy rain
later tonight are in the FFA already. Will see if we can`t trim
it back a bit from the earlier expansion, but likely no trimming
done before we can see where the next few hours takes us.

Prev...
Ridging aloft with deepest layer moisture pooled to the south of
quasi-stationary front draped across central PA this afternoon.
Still sufficient moisture for isold to sct coverage of showers
and now isold tstorms tracking into the Laurel Highlands.
Boundary layer winds still extremely weak, so the main threat
from any of these slow movers is a locally heavy downpour
through late afternoon. NCAR ensemble CAPEs still pointing
toward near 2000 J/kg values and although speed shear is a bit
lacking for a hail threat late this afternoon and early evening.

By early to mid evening, however, increasing large scale
forcing ahead of approaching upper trough should will support
increasing coverage of showers/ thunderstorms with more
organized and possibly training clusters of storms expected.
CAMs have been latching onto this idea since the overnight, and
painting 2-4" amounts over portions of the middle to lower Susq
River Valley. Some of these areas have 3 hr FFG values as low as
1.5". Coordinated a FF Watch for my east central and southeast
Counties with BGM and PHI...focusing on the evening to overnight
timeframe for greatest heavy rainfall threat (running from 21z
through 09z Mon).

Lesser threat of severe given absence of boundary layer winds,
but some storms could produce strong downbursts as well from
impressive water loading. Locally heavy rain and FF threat
lasts into the pre dawn hours, especially middle to lower Susq.
which CAMs suggest will see multiple rounds/clusters with
potentially heavy rainfall.

&&

.SHORT TERM /7 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
Upper trough will pivot through on Monday, bringing a good
chance of additional showers/storms to northeast Pa, while large
scale subsidence in its wake is likely to suppress convection
across the southwest part of the state. With the exception of
northeast Pa, Monday should feature more sunshine than today, as
much lower PW air finally flows into the region.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
Not a lot of change from yesterday. Still going mainly
with dry conditions Tuesday into Wed. Did lower temperatures
a degree or so on Tue, given concern for some clouds and
lack of real strong cool push. Also models show pair of weak
lows just inland from the south shore of the lower Great
Lakes, not sure what to make of this. A strange summer lately.

Still expecting showers and storms on Thursday into the first
part of Friday, with the next cold front.

Went with mainly dry conditions after early Friday.

&&

.AVIATION /01Z MONDAY THROUGH FRIDAY/...
At 00Z the latest radar has showers and thunderstorms moving
through eastern PA bringing heavy rain. These are exiting the
region but will bring -SHRA with VCTS to IPT through 01Z. The
next line is approaching from the west along a boundary which
will reach JST with possible -TSRA between 02Z to 03Z. These
will slide along the southern tier of counties and have timed
them through the TAFs. Latest short term models are showing the
precipitation should exit the region between 09Z to 11Z. Expect
cigs and vsbys to drop to IFR and LIFR shortly after due to low
stratocu and valley fog.

The restrictions should lift between 12Z to 14Z. Another round
of showers and thunderstorms are possible tomorrow afternoon due
to another trough moving through the mid Atlantic. Expect
showers and thunderstorms west to east after 19Z.

Tonight, restrictions return in wake of trough axis, with IFR
conditions likely in the north and east, and MVFR in the central
mountains.

.OUTLOOK...

Tonight...Cig restrictions likely. Scattered TSRA/SHRA.

Mon...AM restrictions likely. Scattered TSRA.

Tue-Wed...AM restrictions north/west. Otherwise no sig wx.

Thu-Fri...Chance of afternoon TSRA/SHRA.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch until 5 AM EDT Monday for PAZ012-027-028-036-
041-042-045-046-049>053-056>059-063>066.

&&

$$
SYNOPSIS...DeVoir
NEAR TERM...Dangelo/DeVoir
SHORT TERM...DeVoir
LONG TERM...Martin
AVIATION...DeVoir/Ceru



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