000
FXUS61 KCTP 250343
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1043 PM EST Sun Jan 24 2021

.SYNOPSIS...
A weak shortwave will pass across the region this evening, then
high pressure will build across northern Pennsylvania Monday
morning. Low pressure lifting out of the Mississippi Valley
will spread a wintry mix across the state Monday night into
Tuesday. Another southern stream shortwave could potentially
affect the area Thursday, then high pressure should build in at
the end of next week.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Warm advection preceding a shortwave tracking across the lower
Grt Lks will bring a bit of spotty light snow to the southwest
portion of the forecast area this evening. Upstream radar
returns and vsbys are not impressive and suggest no accumulation
in most places. However, latest model guidance indicates orographic
enhancement should result in a light accumulation of a dusting
to an inch over the Laurel Highlands. Model soundings indicate
the light snow could end as a bit of freezing drizzle over the
Laurels late tonight, as forcing diminishes behind departing
shortwave, leaving only a shallow cloud layer composed of
supercooled liquid and no ice.

Breaking clouds late tonight should allow temperatures to fall
into the teens over the northern mountains, while cloud cover
holds readings in the 20s elsewhere.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY/...
Low pressure lifting out of the Mississippi Valley will spread
a wintry mix across central Pa late Monday into Tuesday. The
upper level shortwave is progged to weaken as it moves into the
region. However, a surge of Gulf of Mexico moisture overrunning
the approaching warm front and an anomalous low level southeasterly
wind support POPs of 90+ pct across much of the region Monday
night.

Guidance continues to support a precip arrival time of early
evening over the southern tier counties and late Monday night
over the northern tier. Model soundings and latest ensemble data
support a fairly quick transition to fzra/ip over the Laurels
Monday evening. Elsewhere, ensemble mean max wet bulb temps
aloft indicate the changeover from snow to either fzra/ip should
reach into the northeast part of the forecast area by 12Z Tuesday.

The upper level shortwave and plume of deep moisture along
easterly low level jet are progged to lift north of the region
later Tuesday morning, causing precipitation to taper off.
However, lingering low level moisture, combined with easterly
flow, should yield areas of drizzle or perhaps fzdz where temps
remain below freezing over the northern mountains.

Latest WPC and NBM numbers suggest the higher elevations of
Somerset County could exceed 0.25 inches of ice accretion.
Elsewhere, a general 1-2 inches of snow, followed by a bit of
sleet or freezing rain appears likely over much of the forecast
area. Confidence in warning/advisory criteria remains below 80
pct, so will not issue any new headlines this shift. Watch
remains in effect for the higher terrain of the southern Laurels
for the ice potential.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Lingering drizzle, freezing drizzle or snizzle remains possible
into Tuesday night, before the storm system moves off the East
Coast, and a few snow showers are possible across the northern
mountains as colder air returns behind this system.

Wednesday looks like a quiet day between weather systems, with
seasonable temperatures.

The model trend for the past 24 hours has been to push the next
system farther to our south Wednesday night into Thursday. Have
maintained some low PoPs for light snow across southern PA for
this period, but the trend seems to be for less precip this far
north.

There could be some snow showers across the northern and
western highlands Thursday into Friday, as a chillier airmass
returns behind a deepening low that will pull off the East Coast
and out to sea.

Warm advection by next Sunday or Monday could result in some
snow or a wintry mix.

&&

.AVIATION /04Z MONDAY THROUGH FRIDAY/...
Overall, it will just be the lowering and thickening sky cover
overnight, and a few sites will dip to MVFR. Did not drop anyone
into IFR until late tonight in JST, and only there, based on
MOS guidance. While the clouds might be there, little if any
precip is likely at JST from 10-18Z.

The first slug of precip should not arrive until after 18Z
Monday. GFS has a very dry solution and peters this stuff out
very quickly, keep QPF to our south. JST and AOO will be first
on the list for SN, prob around 19-21Z. Shield of precip
continues to slide steadily to the NE through the evening.
Latest model runs have much less QPF in them as there are two or
more rather separate waves of light precip expected. The
dryness of the llvl air likely has something to do with it, too.
P-type does transition over the srn tier to a mix and perhaps a
few hours of ZR at JST and/or AOO. However, the cold air looks
pretty deep as a first volley of precip moves in, so a
transition to sleet first would be more probable than going
straight to ZR.

Outlook...

Mon night-Tues...Widespread restrictions to IFR with light/mdt
snow north and a wintry mix south.

Tues night-Wed...Becoming MVFR.

Wed night-Thu...Restrictions possible with a chance of snow.

Fri...Windy, otherwise no sig wx.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Monday afternoon through Tuesday
morning for PAZ033-034.

&&

$$
SYNOPSIS...Fitzgerald
NEAR TERM...Fitzgerald
SHORT TERM...Fitzgerald/Tyburski
LONG TERM...Martin/Evanego
AVIATION...Dangelo/Gartner