Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 210346

Area Forecast Discussion
National Weather Service State College PA
1046 PM EST Fri Jan 20 2017

Relatively mild, but cloudy and unsettled conditions will
persist through the weekend before cooler air makes a return
next week.

A complex and slow moving storm system is expected to move
across the deep south then swing northeast along the
Appalachians Sunday afternoon and night. The storm will then
exit off the Mid Atlantic coast Monday and Tuesday and bring
rain and perhaps a return of wintry weather. Much colder
temperatures will arrive at the end of next week.


Current Obs and gridded LAMP and HRRR vsbys point twd the need
of a Dense Fog Advisory over the NW Mtns and numerous SE
counties and Schuylkill cty overnight through 13Z Sat. Sent out
a recent collaboration message to surrounding WFOs regarding

A few dwindling areas of light rain were drifting across the
northern mtns of PA this evening. Elsewhere, skies were mostly
cloudy to overcast with nothing more than some patchy light
drizzle and areas of fog.

A warm front close to the I-76 corridor in southern PA will lift
slowly north across the forecast area overnight and Saturday.
increasing dewpoints (into the lower 40s) over the colder,
moist ground will allow fog to gradually thicken up to between
1/2SM and 1SM in many locations.

Should any clearing occur, vsbys could quickly dip to AOB 1/4SM.
In that case, consideration will have to be given for a Dense
Fog Advisory.

The temps will be nearly steady in most areas overnight, ranging
from the upper 40s to around 50F across the Laurel Highlands,
the lower to mid 40s across the Southern Valleys and NW mtns,
and mid to upper 30s in the Central Valleys and Middle Susq


Some fog and drizzle will linger in the morning, and even into
the afternoon on the ridges. Few if any breaks in the clouds are
expected outside the far lower Susq as the lowest 3kft remain
nearly saturated. Maxes are a tough call with lots of cloud
cover, but an 8-12F rise is feasible. Will run with maxes just a
hair under MOS blend. The central counties will probably top out
in the m-u40s, but most other places will. 60F is possible, but
not likely, in the Laurels and Warren Co.


As the upper ridge is forecast to re-establish itself over the
eastern U.S. early in the period, a very complex storm system is
now forecasted to be settling over the Southwestern US by
Saturday evening. This southern stream low should continue to
track through the southern states before turning northeast over
the eastern US Sunday night into early next week. The mid to
long range models continue to trend warmer Sunday night into
Monday. 850mb and 925mb Temperatures continue to be above 0C
though a snow/rain mix remains possible in the higher
elevations. Have rain as the main precipitation type. The
forecast question through this period is QPF amounts. Based on
latest models, blends, ensembles and national guidance, have
increased QPF slightly based on PWATS, the moist southerly
flow. One limiting factor could be probability of snow/rain mix,
so higher QPFs are possible in the southeast. There remains a
fairly large spread in QPF amounts in the plumes so will
probably need to adjust amounts for later runs.

Snow is possible beginning Monday across the Laurels within the
region of greatest thickness cooling, then later Monday into
Tuesday across the northern mountians and toward the Western
Poconos. The combination of A backdoor Cfront sliding SWWD from
New England and increasing baroclinicity as the deep low
approaches the Mid Atlantic Monday night into Tuesday will allow
the low to maintain its intensity and pull colder/sub-freezing
air back into the NE and NCENT mtns.

Most signif snow in oour CWA appears to target the Laurels and
perhaps Sullivan and Tioga ctys in the NE.

Any high pressure over the region will be short lived as a
upper level low will settle over Eastern Canada. That system is
progged to drag a cold front through the mid Atlantic Wednesday.

After our early week storm system, the eastern ridge is made to
make a rapid rebound, even if for just a short time around
midweek. A fast moving shortwave quickly chews the top off the
ridge with cyclonic westerly flow by week`s end. Colder air
looks to advect into the region bringing in more winter like
temperatures late next week.


IFR/LIFR stratus/fog covers nearly all of central Pa this
evening northeast of a stalled warm front, which runs from
western Pa southward along the spine of the Appalachian Mtns.
Model soundings support continued low CIGs/fog overnight
northeast of this stalled boundary. Exception may be at JST,
which is straddling the warm front and is VFR at 03Z. A very
close call here, as even a slight retrogression westward of
front could lead to a return to IFR at JST overnight.

Little improvement expected east of the Appalachians on
Saturday, as models continue to show persistent low level
moisture trapped beneath inversion to the northeast of stalled
warm front. Best conditions will almost certainly be at JST,
where VFR conditions appear likely west of front. Elsewhere,
some modest improvement appears possible by afternoon, but
IFR/low MVFR CIGs appear likely to persist through the day.


Sun...Low CIGs likely. Rain advances from S-N late.

Mon...Rain/low CIGs likely.

Tue...AM rain/snow and low CIGs possible.

Wed...Reduced CIGs/showers possible NW.




NEAR TERM...Dangelo/Lambert
SHORT TERM...Dangelo
LONG TERM...Lambert/Ceru
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