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FXUS61 KCTP 211509
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1009 AM EST Wed Feb 21 2018

.SYNOPSIS...

A cold front will push southeast across the area this afternoon
and evening, then stall out in the vicinity of the Mason-Dixon
line or across the Virginias late this week into the upcoming
weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

The cold front as of 10AM extends from between BFD and ERI
southwest into south-central OH. Radar indicates this is an
almost classic anafront with an area of rain along and behind
the front.

It will be another unseasonably warm day for most of the
forecast area with highs reaching well up into the 60s and 70s
before cooler starts to ooze in behind the cold front. These
temps will depart by an amazing 35 deg F from normal highs in
Late Feb.

The HRRR shows the cold front from about IPT to JST by 18Z/1PM,
and passing through the lower Susq Valley between 4 and 7PM. I
inserted the mention of thunder over the SE given the latest
HRRR generating some instability in the warm and moist airmass.
Dewpoints are approaching 60 over the SE where it no doubt feels
quite humid for the time of year.

Another trend in the HRRR and NAM based CAMs is to show the rain
really falling apart as it enters the Central Mountains today,
becoming more scattered and showery. I trimmed POPs a bit to try
and depict this more optimistic scenario. Rainfall totals will
be generally light and less than 0.10 of an inch.



&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...

Periods of rain (with a several hour period of icing from
freezing rain across northern PA) is expected late tonight
through Thur morning across the northern half of PA. A light
accumulation of snow could precede the freezing rain across the
Northern Mountains early Thursday.

Colder/drier air will temporarily filter south into the region
this evening thanks to strong 1040 mb high pressure buildings
eastward from the Midwest. Stalled frontal boundary south of Pa
will begin to return northward late tonight, spreading rain into
much of the region, with mixed precip likely along the northern
tier.

The cold front will become quasi-stationary near the MD line
tonight. The wavy frontal boundary will bring periods of rain
into the weekend, with several (to as much as 8) hour period of
mixed wintry precip likely across mainly the Central and
northern mountains tonight and Thu morning, thanks to an
increasing and moderately strong northerly, 1000 mb Ageostrophic
flow that will serve to pump shallow/sub-freezing air south
into the region.

Confidence is moderate with respect to the exact ptype details
(and the location and amount of fzra across primarily the
northern Mtns of PA). However, there is at least some risk for
a light snow and/or ice accumulation. We're in good agreement
with WPC's Winter Weather graphics ATTM, with a coating to 2
inches of snow possible at the onset across parts of
northcentral and NW PA, before a changeover to sleet and or
Freezing Rain.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Forecast for Thursday into Friday looks cloudy and damp with
periods of light rain/drizzle and areas of fog. The fog will be
locally dense at times, especially on East-Facing slopes and
ridgetops during the overnight and early to mid morning hours.

Stalled out sfc front across the Virginias and Ohio River
Valley and SW flow aloft will be the conduit for a few waves of
low pressure to ripple NE along, and bring us this rather dismal
weather.

There is the potential for a significant change in practical
weather...if frontal position changes north or south very much.

Still looking like another warm up on Sunday. Potential for
some heavy showers across the west...but several days out.

Still looks dry behind the front Sunday Night...so I took
out the showers of the fcst after 06Z Monday.

Left Monday into Tuesday dry...weak system fcst to cut under
the ridge...but not seeing much moisture with this.

Another round or two or rain is likely over the weekend. We
will need to monitor the potential for flooding especially
across south- central PA where the ground is very saturated from
previous rain/snowmelt and streamflows are well above normal.

&&

.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
Patchy dense fog impacting eastern portions of CWA (generally
east of the Susq River) this morning under strong low level
inversion. Vsbys should improve back to VFR at MDT-LNS by ~14z
while it may take a couple of hours longer in the protected
valley of IPT. Elsewhere, outside of some very patchy fog,
conditions will be primarily VFR until arrival of a cold front.

LLWS the first half of the day will gradually weaken, but also
begin to mix down to the surface as inversion erodes - allowing
SW winds to pick up to around 10 mph gusting to 18 mph across
the western valleys and 15 mph gust to 25 mph on the ridges.
Winds over the east will remain generally less than 10 mph.

A sharp cold front will move into the NW Mtns late this morning,
bringing reductions in rain. These impacts will attempt to
spread into portions of the central mountains during the
afternoon before improvement back to VFR this evening. Showers
do spread into the SE late this afternoon as well, but
conditions will remain primarily VFR there. Winds turn to the
west over the Lower Susq and NW elsewhere.

An active second half of the week follows, as several weak
waves of low pressure bringing bouts of rain, and even some
light freezing precipitation to the north Thu into early Fri.

Outlook...

Thu...Widespread restrictions in rain south/wintry mix north.

Fri...Widespread restrictions in periods of rain. Some
improvement poss SW late.

Sat...Rain remains likely. Widespread restrictions north,
gradual improvement south.

Sun...Widespread restrictions likely in periods of rain.

&&

.HYDROLOGY...
Recent rainfall and snowmelt has resulted in wet soil and well
above normal streamflows across much of the area especially
south-central PA. Rainfall of 0.50 to 1.00 inch is forecast
between Wednesday and Thursday night, with additional rainfall
likely into/over the weekend. River flood potential (including
small streams, creeks and tributaries) is above normal and we
will continue to monitor the risk in the coming days.

&&

.CLIMATE...
It Looks like another day of record highs across southern Pa
today. Here are current records for today, Wednesday February
21st:

MDT: 71/1997
IPT: 69/1930
BFD: 64/1997
AOO: 71/1997

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...La Corte/Lambert
NEAR TERM...La Corte/Lambert
SHORT TERM...DeVoir/Fitzgerald
LONG TERM...Lambert/Martin
AVIATION...RXR
HYDROLOGY...
CLIMATE...
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