Area Forecast Discussion
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FXUS61 KCTP 212003
Area Forecast Discussion
National Weather Service State College PA
303 PM EST Sat Jan 21 2017
Unseasonably mild weather will continue through the weekend.
A complex and dynamic storm system will bring the potential for
heavy rain, accumulating snow and strong winds to portions of
Central PA on Monday. The mild conditions will last into the
middle of next week before a pattern change brings colder air
and more seasonable temperatures to close out the month.
.NEAR TERM /THROUGH TONIGHT/...
Dense fog has largely dissipated but still plenty of low clouds
and 1-3SM visibility in the central and southeast valleys. Have
adjusted max T down a few degrees in these areas which will not
see the sun today. On the flip side, a spring-like day can be
found along and west of the Allegheny Front with 55-65 degree
readings over the western 1/3 of PA. Even a few cu noted on the
vis sat now being overrun by increasing high clouds from the SW.
Latest thinking is that low clouds and fog will expand/redevelop
tonight into Sunday morning particularly from the central ridge
and valley region into the Susq. valley. Later shifts may need
to issue another dense fog advisory. Otherwise, cloudy and
unseasonably mild overnight with minimum temperatures +20-30
degrees above normal for late January. There could be some
pockets of light rain/drizzle but generally kept POPs below 20
percent. Rainfall associated with surface low tracking northeast
from GA/AL is fcst by the models to stay southeast of the area.
.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
Closed mid-level low tracks from the ARKLATEX to western VA/NC
by 23/12z. Moisture and inflow will increase ahead of the mid-
level system and should support rainfall pivoting northward into
southern areas by the end of the period. Model QPFs indicate
the main rain axis stays to the south of the PA/MD line although
placement highly anomalous easterly flow of high PW air into e-w
frontal zone has me a bit concerned. One thing of note is an
increase in winds over the Lower Susq. valley with gusts over 40
mph possible by daybreak Monday. Temperatures stay very mild
and well-above normal for this time of year.
.LONG TERM /MONDAY THROUGH SATURDAY/...
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
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.
.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
VFR over the western 1/3 this aftn and eve should trend toward
MVFR tonight with IFR possible at KBFD. Vis satellite and obs
trends indicate some improvement in cigs/vis over the central
and eastern TAFs. However, expect widespread IFR-LIFR conditions
to continue/redevelop overnight with local cigs/vis AOB airfield
mins into Sunday morning.
Sun...MVFR/IFR. Rain spreads south-north into Sunday night.
Mon...Rain/low CIGs likely.
Tue...AM rain/snow and low CIGs possible.
Wed...Reduced CIGs/showers possible NW.
Thu...MVFR/IFR in rain/snow showers mainly west.
LONG TERM...La Corte