Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 200409
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1109 PM EST Fri Jan 19 2018

.SYNOPSIS...
A large area of high pressure centered over the Lower
Mississippi Valley will maintain fair skies for the next few
days. Temperatures will climb above normal over the upcoming
days with mainly dry weather continuing. A cold front will move
through the area later Monday night and early Tuesday.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Minor changes made to the previous evening update - mainly in
terms of hourly temps and wind.

Variable amounts of cirrus clouds will drift southeast across
the region overnight, with the greatest percentage over northern
and western PA.

Temps will be milder than normal by 6-10 degrees F in most
places overnight thanks to a 10-15 kt SW wind across northern
and western parts of the CWA...with gusts to around 20 kts. A
few locations across the Lower- Mid Susq Valley could see temps
dip to around normal (in the low 20s) as a result of mainly
clear skies and a decoupled boundary layer with nearly calm air.

Elsewhere, min temps early Saturday will range from the mid 20s
across the north, to the upper 20s to around 30F over the
southern half of the state.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
After a mostly Sunny morning in most places, the operational
NAM, GFS and RAP show a rather shallow layer of stratocu clouds
adevcting ESE and into the western zones duirng the late
morning/early afternoon hours, and later in the afternoon or
evening across the Susq Valley. The latest ensemble MOS pops
continue to show a small chance of some light rain...mixed with
wet snow flakes...reaching my far NW counties around sunset
Saturday.

Otherwise more of the same is expected with a gradual increase
in mid and high clouds throughout the day.

Highs on Saturday will range from near 40F north to the lower
50s across the south. However, a brisk westerly wind (averaging
in the mid to upper teens (KTS) with gusts as high as 30 KTS
during the late morning and afternoon Western high terrain and
20-25 kts elsewhere) will make it feel notably cooler than the
actual air temp - or in the upper 20s across the higher terrain
of the north and west, and upper 30s in the SE.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Another January thaw will bring a period of relatively mild
weather to Central PA into 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. The progressive pattern should keep the cool
down through the middle part of next week rather brief before
temperatures moderate/trend warmer into next weekend.

A surge of warm advection 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. Examination of thermal/moisture profiles
specifically sfc temps and maxTw aloft suggest some patchy
freezing drizzle is possible over parts of north-central PA Sat
night and Sun night. The other concern may be black ice as snow
melts during the day and then freezes at night.

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

The most likely period for widespread rain is Monday night into
early Tuesday along/ahead of south-southwesterly LLJ axis and
cold/occluded front. A 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.

Winds look rather blustery from later Tuesday into Wednesday on
the backside of the low pressure system and may approach
advisory criteria. Snow showers are likely downwind of Lake Erie
into Wed night. Dry wx with moderating temperatures Thu-Fri.

&&

.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
Widespread VFR will continue overnight and much of Saturday
as high pressure maintains control of the local weather
pattern.

A MVFR stratocu/stratus deck may advect East into the Western
zones during the afternoon, and late in the day or evening
across the SE.

Some very light snow or flurries could develop from this cloud
deck later Sat afternoon and evening over favorable upslope
areas of the Alleghenies (KBFD and KJST TAF sites), as the
clouds will be 1000 feet or so thicker. This will be watched
closely and likely included in TAF updates.


Outlook...

Sun...Mainly VFR.

Mon...Reduced conditions with rain showers associated with an
approaching cold front.

Tue...MVFR/IFR with snow showers west and north. MVFR/VFR
central and eastern terminals.

Wed...MVFR with snow showers west and north. VFR central and
eastern terminals.

&&

.HYDROLOGY...
Main concern is watching water levels rise on Susq downstream on
Harrisburg. Marietta gage /MRTP1/ continues its slow rise as ice
builds up downstream. Gage above action stage and there is some
minor flood concerns in Wrightsville ongoing. The Flood Watch
for this area has been extended through the weekend, set to
expire 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.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Monday afternoon for PAZ065-066.

&&

$$
SYNOPSIS...La Corte
NEAR TERM...Lambert
SHORT TERM...La Corte/Lambert
LONG TERM...Steinbugl
AVIATION...La Corte
HYDROLOGY...Ross


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