Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 291136
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
736 AM EDT Mon May 29 2017

.SYNOPSIS...
A trough of low pressure will stall out over central and
eastern PA today. Low pressure will be centered over northern
Ontario for most of the week and will lead to a period of
slightly cooler than normal temperatures. A series of fronts
will pass through and create many chances for showers through
the week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Good news for the western counties as the showers are moving to
the east of them now and ending the heavy rain threat. The
showers should keep moving and be off to the east of the area by
mid-morning or noon at the latest. There are some breaks in the
clouds over OH, but the clearing process will likely be slow for
central PA. Only tweaks to timing and QPF for this update.

Prev...
Widespread SHRA rolling across the area now. This should be the
last huurah for the heavy rain, as a strong short wave
trough/MCV is easily seen in the radar loops zipping northeast
through northern PA. The surface front(s) are just about washed
into one general trough with it`s axis over far western PA at
08Z. This trough should push eastward another 150 miles, but
looks like it stalls out right over the Susq River. Showers
should become more scattered shortly in the west with little
additional rainfall after 5 or 6 am. This will be welcome news
for there is some minor flooding on-going in Clearfield Co.

RAP now has a decent handle on where the precip is and the
movement of the cells/elements. IR sat pics show that the
convection moving into the Laurels has cooling tops, and will
continue to produce some heavier rain rates. We do have a high
confidence in the RAP forecast of rain placement & rates for the
next few hours. Not much lightning left in the showers
- and most of it is confined to just the Laurels.

Expect that the showers will be done across the western 1/2 to
2/3rds of the CWA by 10 or 11 am. But the stalling of the sfc
trough means there will be a focusing mechanism in place. If
the sun breaks through and there can be some good heating in the
Susq Valley, there could be a line of showers (maybe thunder)
develop later today.

Across the west, the air will dry out a little with a west wind
of 10-12 MPH and a higher gust possible this aftn. Maxes will be
highly dependent of the amount of clearing that can develop. RAP
and NAM llvl RH plots yield a less-than-sunny forecast for the
eastern third and over the Alleghenies. However, the late May
should combine with the wind/mixing to make it pretty sunny in
the western half of the area this aftn. The clearing would come
late in the day for the east, and have nudged temps down a
little there.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
Brief ridging will allow the skies to clear over most of the
area this evening, and residual moisture may lead to areas of
fog, especially in the eastern valleys. Mins will dip into the
50s for most, as the dewpoints will be the bottom limit.

A weak sfc trough will be pushed into the area from the
northwest tonight. 8H temps fall a bit over the NW. Heights
fall just a little, too, so some precip is possible before
sunrise Tuesday over the northwestern third of the area, but it
should be light. The trough begins to catch the stalled trough
over the eastern counties. The southerly or southeasterly wind
will yield good convergence and will crank up some showers and
thunderstorms. Have painted high POPs for the area, but the
amount/severity of destabilization is in question with the
clouds in the NE early in the day. NAM cranks out 1500joules of
CAPE and LI drops to -2 or so in the mid-day and aftn on Tues.
SPC marginal Risk of svr wx for Day 2 (Tues) is painted across
our eastern half, focused on the peak heating time. Will
continue to mention this in the HWO.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
The long term period will be dominated by a large upper level
low the will be slowly moving through the upper Great Lakes and
southern Canada. As that quasi stationary low slowly moves to
the northeast, it will bring surges of cool moist air across the
region.

Several successive shortwave will move through mid to late week
which will bring the possibility of scattered showers with
preference for the majority of the QPF (albeit quite light at
that) to be across the typical west-nwrly flow upslope prone
areas of the Laurel highlands and NW mtns. The chance for any
thunder will be very minimal Wed and Thursday.

Generally dry NW flow occurs late in the week into next weekend as
a 1020 sfc high over the upper midwest Friday evening builds SE twd
the region. Pops Thur night through Fri night will be 30 percent or
less.

Late in the week the models begin to diverge on the location
and timing of the upper level low so there is less confidence on
precipitation late in the week. However depending where the
boundary sets up there could be periods of showers Friday
through Saturday, though currently should be mainly along the
Southern border.

&&

.AVIATION /11Z MONDAY THROUGH FRIDAY/...
Widespread sub VFR cigs across the airspace this morning after
overnight rain and thunderstorms will persist this morning. Slow
imporovement exected into this afternoon with main area of pcpn
having moved east of the region.

Depending on how much clearing occurs/remains this evening,
widespread fog formation is possible regionwide tonight.


.OUTLOOK...

Tue...Chance of showers and thunderstorms.

Wed...Chance of showers.

Thu...No sig wx expected.

Fri...Chance of showers and thunderstorms.

&&

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

&&

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



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