Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 211218

Area Forecast Discussion
National Weather Service State College PA
718 AM EST Sun Jan 21 2018

A warm frontal boundary drifting slowly north across the region
today and Monday will bring some occasional light rain or
drizzle into early Monday. A potent area of low pressure moving
northeast across the great Lakes Tuesday will push its southward
trailing cold front east through Pennsylvania during the morning
to midday hours Tuesday. Temperatures will rise above normal
today and stay there through early Tuesday, before falling back
to near or slightly below normal Wednesday and Thursday. A
rebound in temperatures to above normal levels will occur again
for next weekend.


The risk of ice jam flooding will continue over the weekend and
into early next week. See the hydro section for more details.

An extensive shield of strato cu has advected east across
practically the entire CWA over the past several hours. as this
cloud deck slowly lowers and thickens up today, we`ll see some
areas of light rain or drizzle develop (mainly across the
northwest half of the state). Little or no chance for measurable
precip exists near and to the SE of the I-81 corridor.

Winds will be light for the most part and from the southwest.
Temps that are currently about 5-8 deg F above normal across the
Susq Valley, and nearly 20 deg F above normal across the
Central and NW Mtns will warm into the 40s in all locations
today, with a few spots in southern PA reaching the 50 deg mark.


The start of warm advection Sunday night and Monday ahead of a
strengthening Mississippi Valley/Great Lakes cyclone will
impinge on a retreating thermal gradient between I-80 and I-90.
Forecast soundings indicate moisture will be rather shallow
initially with areas of light rain confined mainly to the
western and northern parts of the area. Elsewhere expect low
clouds to develop with pockets of drizzle/mist and fog.

As the cyclone approaches, Monday will see the light showers
retreat to the north with the warm front (thermal boundary).


Another January thaw will bring a period of relatively mild
weather to Central PA through early next week. Temperatures are
not expected to be as warm as the previous thaw (late last
week), but departures should reach +10 to +15 degrees above
average for mid to late January, peaking Monday in the NW and
Mon into Tues in the SE. The progressive pattern will keep the
cool down during the middle/late part of next week rather brief
before temperatures moderate/trend warmer into next weekend.

A weak secondary low may form in the lee of the Appalachians
and support a period of enhanced rainfall over the eastern 1/2
of PA Tuesday morning. At this time, the total rainfall forecast
for early next week does not appear to be as heavy as Jan.
11-12. The most likely period for widespread rain is Monday
night into early Tuesday along/ahead of south-southwesterly LLJ
axis and cold/occluded front.

Winds look rather blustery from later Tuesday into Wednesday on
the backside of the low pressure system as colder air filters
back in. Snow showers are likely downwind of Lake Erie into Wed
night. Dry wx with moderating temperatures Thu-Fri under high
pressure. Some showers may sneak into the NW Sat as weaker low
pressure system lifts across the Great Lakes, with better
chances for rain with another low on Sunday.



Low stratu cu continues to move over the region this morning.
MVFR is over all central and eastern TAF sites, with IFR and
lower at BFD and JST. Expect these conditions to continue
through the morning. Latest HRRR continues to show chances for
light rain/drizzle will increase as the morning continues for
the western TAF sites, with AOO, IPT and UNV having IFR possible
tonight into tomorrow morning. Expect restrictions to continue
into tomorrow morning with improvements from the south to the
north by 18Z Monday afternoon.


Sun PM...SCT SHRA - mainly in the north. Otherwise MVFR S and

Mon...Reduced flight categories with rain showers associated
with an approaching cold front - mainly N. Improvement expected
from S-N thru the day.



Thurs...No sig wx.


Main concern is watching water levels rise on Susq downstream on
Harrisburg. Marietta gage /MRTP1/ being only about 2.5 FT below
FS of 49 FT continues to fluctuate by 1-2 feet over short
periods of time due to ice effects.

Gage above action stage and there is some minor flood concerns
in Wrightsville ongoing. The Flood Watch for this area extends
into Monday afternoon.

With milder temperatures there is potential for ice movement,
as well as slow ice deterioration/thinning with time. All areas
near rivers and streams that have significant ice buildup should
monitor water levels closely for the next several days.


Flood Watch through Monday afternoon for PAZ065-066.


NEAR TERM...Dangelo/DeVoir
SHORT TERM...Dangelo
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