Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 211128

Area Forecast Discussion
National Weather Service State College PA
628 AM EST Sat Jan 21 2017

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

A complex storm system is expected to move across the deep
south then swing northeast along the Appalachians Sunday
afternoon and night. The storm will then move slowly off the
Mid Atlantic coast Monday and Tuesday. Colder temperatures will
arrive at the end of next week.


Plentiful low level moisture and little in the way of cloudiness
above have helped create conditions conducive to fairly
widespread dense fog. We expanded the previous advisory to cover
all but Cambria-Somerset where milder air is in place helping
suppress the fog.

A diffuse warm front should finally either pass to our north or
fall apart altogether, allowing milder air to be enjoyed by
most of us in the ridge-valley areas of central PA. Highs
today, even though we will remain cloudy, will average some
15-25 deg above normal.

Other than some patchy drizzle, we should stay mainly dry and
unseasonably mild today under the southerly flow on the back
side of the surface high off the Mid Atlantic coast.

The damp but mild southerly flow will continue overnight. Near
term models splash some very light QPF around the region, but
don`t agree on where exactly. Consensus pops favor southern
areas with the moist flow so I opted for a small chance of light
rain and some patchy drizzle being the most likely outcome.

Again it will be unseasonably mild, some 20-30 deg above


As the storm system tracks east from Tennessee on Sunday, the
local flow will become more SELY and tend to increase. The
short term models keep the bulk of the rain associated with the
storm still off to our south, but the increasingly moist flow
should help support at least some light rain, especially over
southern areas. GEFS pops show a good chance of rain everywhere
with a near certainty over the south where I painted my highest

The rain will trim a few deg off the high temps, but it will
still remain much warmer than normal for this, the
climatologically coldest time of the winter.


The lustiest GFS/ECMWF as well as the EC ensemble are in pretty
good agreement in tracking a  surface low east through the
Carolinas-southern Virginia before redeveloping it off the
Delmarva and tracking it offshore Monday and Tuesday. We start
off very warm so it`s still uncertain if or how much snow will
fall. The period of most intense ascent/dynamic cooling looks to
be Monday morning into the early afternoon. The GFS/ECMWF/GEFS
all show very marginal cold air being generated at the peak of
the storm. At this stage it looks like it will be a very
elevation dependent precip type, which the EC ensemble agrees
with, painting something along the lines of 2-4 inches of snow
from the Laurels up into the northern mountain. The ECENS is
notoriously generous with snow amounts, but I like the
portrayal of my higher elevation areas. The GEFS plumes show
BFD with the most snowy members, with mostly rain even down into
JST. So it all points to a highly uncertain forecast.

Another consideration will be the potential for heavy rain. The
GEFS develops a strong ESE low level jet of about 50-60kt at
850mb. In the ensemble that figures to be a widespread 5-6
sigma easterly anomaly. The ensemble shows a high likelihood of
at least an inch of rain in 24 hours between Sunday night and
Monday night, with other features pointing to the Monday morning
into afternoon timeframe. RFC guidance suggests rain amounts of
around 2 - 2.5 inches in 6 hours will start to cause flooding
problems, so as the event nears we will have another thing to
focus on.

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.


Made a few adjustments, mainly the later period.

12Z TAFS sent.

IFR/LIFR stratus/dense fog will be across most of the area this
morning. JST at times will be VFR, as they are in the warmer
air west of the mountains.

Little improvement expected east of the Appalachians today,
as low level moisture remains 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.

An extended period of rain expected late Sunday into Tue.


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.


Dense Fog Advisory until 8 AM EST this morning for PAZ004>006-


NEAR TERM...La Corte
LONG TERM...La Corte
AVIATION...Martin is the U.S. government's official web portal to all federal, state and local government web resources and services.