Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 230528
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1228 AM EST Mon Jan 23 2017

.SYNOPSIS...
A multifaceted storm will bring drenching rain, elevation-
driven snow and gusty winds to Central Pennsylvania on Monday.
High pressure and unseasonably mild conditions will briefly
return for midweek before a pattern change brings colder
temperatures and lake effect snow to close out the month.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Low visibilities in stubborn denser fog finally rising a bit
from Altoona through State College up toward Williamsport where
a swath of fog has been persistent through the day and into this
evening.

PoPs currently trending upward across the region as moisture
and lift increases ahead of the strong storm system tracking
northeast across the Southern Appalachians. Band of light rain
developed over northern mountains this eve, but QPFs were
minimal. PoPs increase from south to north tonight, as latest
radar and HRRR progs shows rain continuing to spread north of
the Mason-Dixon line overnight. Also, winds will pick up from
the east over the lower susq toward sunrise, with speeds rising
to 20mph and getting gusty later in the morning.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TUESDAY/...
Rain will increase in coverage and intensity from south to
north through daybreak Monday. A tightening pressure gradient
between deepening low pressure in the Carolinas and high
pressure in eastern Quebec will produce strong/gusty east winds
early Monday morning and continue through Monday afternoon.
Issued a wind advisory for most of the lower Susquehanna Valley
with max wind gusts 45-50mph.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
All model data tracking closed upper low northeast across
Virginia Monday. A steady rain will overspread Pa from north to
south as strong upper lvl divergence, anomalous easterly low
lvl jet/PWATS work into the state. Thermal profiles initially
warm enough for rain everywhere. However, dynamic cooling
associated with arrival of strongest forcing will likely result
in a changeover to wet snow over the higher terrain of central
Pa. Forecast soundings suggest the highest elevations of the
Laurels/Northern Mtns could mix with or change to wet snow
around midday. By later in the day, snow could become more than
just a higher elevation threat, with thermal profiles even as
far east as AOO/UNV cooling sufficiently for all snow. Limiting
factor in terms of accumulation will be marginal boundary layer
temps and warm ground. The threat is for several inches of heavy
wet snow, especially favoring the higher elevations, across
northern Pa. A winter storm watch has been issued for the
northern counties, where 6+ inches appears possible, mainly over
the higher terrain.

Biggest threat across the Lower Susq Valley will likely be
gusty winds, the result of tightening pressure gradient
between approaching low pressure and high north of New England.
Bufkit soundings indicate wind gusts in excess of 40kts are
likely across southeast Pa, as low lvl jet swings through
Monday. Per coordination with LWX/PHI, have issued a wind
advisory for this area.

Lastly, still monitoring the potential for minor flooding.
Target area for the heaviest rain is across the south central
part of the state, where orographic forcing at nose of powerful
easterly low level jet will play a role. Mean QPF from both SREF
and GEFS max out around 1.5 inches in this region, which would
be a beneficial rainfall. However, given FFG/FFH values around
2 inches, can`t rule out some minor flooding.

The surface low will reach our latitude between about 6-12Z
Tuesday, an old rule of thumb that dictated when the steady
precip tends to taper off. Upper ridging will quickly build into
the region later Tuesday into early Wednesday, bringing a short
period of fair and mild wx.

A pattern shift is advertised for the second half of the week
as low pressure takes up residence over eastern Canada, and
despite a tenacious ridge over the northern Caribbean and
Bahamas, models carve out a long wave trough over the eastern US
with a return to seasonable cold by the end of the week into
next weekend.

The ridge in the west and trough in the east is also usually a
good one for winter storminess, but the deterministic ECMWF and
GFS don`t show much more than a series of clipper type systems
that promise an extended period of clouds and scattered mainly
mountain snow showers that should continue through next weekend
into the week after.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
Steady rain still well to the south. Main issue early on is
dense fog.

06Z TAFS sent.

Earlier discussion below.

With the showers moving in, and winds beginning to pick up, much
of the LIFR conditions have improved, but while visibilities
have improved, ceilings continue to lower in response to
easterly flow.

After several hours of variable cig and vis conditions, expect
most areas to settle into mainly IFR conditions late tonight
and much of Monday, with a widespread rain event moving into the
region. Later in the period across the west and north,
conditions expected to deteriorate even more as we approach
20z-00z...with rain mixing with and possibly changing to snow.
Extent and degree of changeover still in question, but dynamic
cooling may bring some rain/snow mix into most areas except the
far southeastern airfields.

Additionally, strong gusty winds will impact southern airfields
beginning late tonight and Monday. KMDT/KLNS may see gusts
approaching 30-35+KT. Low level jet will introduce LLWS at most
central and southern airfields late tonight and Monday.

Outlook...

Tue...Widespread sub-VFR with some improvement by aftn. Rain/snow
ending in the morning. Gusty winds from NNW decreasing late.

Wed...Low cigs/rain possible western 1/2. Breezy late.

Thu-Fri...MVFR/IFR in rain/snow showers west. MVFR to VFR east.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from noon EST today through Tuesday morning
for PAZ005-006-037-041-042.
Wind Advisory from 5 AM early this morning to 4 PM EST this
afternoon for PAZ057-059-064>066.

&&

$$
SYNOPSIS...RXR/Steinbugl
NEAR TERM...RXR/Steinbugl
SHORT TERM...RXR/Steinbugl
LONG TERM...Fitzgerald/La Corte
AVIATION...Jung/Martin


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