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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

                            
000
FXUS61 KCTP 231220
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
720 AM EST Sat Feb 23 2019

.SYNOPSIS...
High pressure over the Hudson Valley will slide east and off
the new England Coast this afternoon. 

A moist and deepening southeasterly flow off the Atlantic Ocean 
will leading to lowering and thickening clouds today with some 
light rain or drizzle spreading Northeast across the state later 
this morning and afternoon. 

The ridge tops of Central and Northwestern Pennsylvania, 
including the Laurel Highlands could be just cold enough for the 
light precipitation to freeze on contact with the cold ground and 
elevated untreated surfaces. 

A soaking rain will follow ahead of a cold front for tonight. 

Gusty and potentially damaging westerly wind gusts will develop 
in the wake of the cold front late Sunday morning, and will continue 
through Midday Monday.

Occasional snow showers over the Northwest Mountains Sunday 
afternoon and night could accumulate a few inches by daybreak 
Monday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Widespread cirrostratus shield continues to blanket the entire 
state early today, with the thickest clouds located across the 
southern third of PA. 

Daybreak readings/low temps will range from the low 20s over 
the northern mountains, to between 28-32F in the south.

Lowering cloud bases will occur through today as the dry, 0.25
to 0.40 PWAT airmass is replaced by increasing moisture at llvls
being transported off the western Atlantic via a strengthening
southeasterly flow in the 925-850 mb layer, and a wide plume of
mid and high level moisture streaming northeast from the Gulf 
Coast region and all the way from the Equatorial Pacific.

Expect the cloud bases to gradually lower to a stratus deck
(1000 ft agl or lower on the ridge tops and SE facing slopes) late
this morning (SW zones) and this afternoon across the
Central and Northern Mtns. The clouds will thicken enough and
ample orographic component to the moist llvl flow will occur to
produce some light rain or drizzle during the midday and
afternoon hours, and model consensus (including the NAM and
HREF) appears to hold the ridges with elevations AOA 1800 ft 
MSL cold enough for some light freezing rain/-FZDZ this
afternoon into this evening (which is normally a time of lower
probability for and impact by freezing precip). That being said,
will limit any impact statements for now in the Hazardous
Weather Outlook, though it's not out of the question for a
Winter Weather Advisory to be issued, based on radar coverage 
and updated temps from high res model guidance. 

Liq Equivalent QPF through 00Z Sunday will vary from a few to
svrl hundredths of an inch across the NE half of the CWA, to
around an one tenth of an inch in the southwest zones.

Max temps this afternoon will range from the mid to upper 30s in
the Central and Northern Valleys (and lower 40s across the Lower
Susq Valley) to near freezing on the ridges.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
Higher PWAT air (between 1-1.25 inches) will spread in from the
Ohio River Valley by tonight and a soaking rainfall will follow
for an approximate 7 to 9 hour period as uvvel increases at the
nose of a 55 to 65 kt swrly LLJ. 

Consensus rainfall amounts are about 30-40 percent lower than
model depictions from 24 hours ago and should average between 4
and 5 tenths of an inch across the northern half of PA, to
nearly 0.75 of an inch in the far southeast. 

This amount of upcoming rain and runoff into streams and creeks
will be very manageable since a significant percentage of the 
snow from the midweek storm melted/sublimated Thursday and
Friday, and most will have already flowed into the larger tribs
and rivers before the bulk of the rain arrives late today
through early Sunday.

Focus will then shift toward the potential of strong winds 
Sunday afternoon through Monday afternoon, as a potent cold 
front sweeps through the area, allowing strong winds associated 
with Grt Lks storm to mix to ground level. This scenario of a 
powerful low passing north of Pa fits the pattern we see with 
our strongest winds across central Pa and a quick look at model 
850mb winds suggest >50kt gusts are possible.

A High Wind Watch continues for our Entire Area from Late 
Morning Sunday into Monday afternoon, with strongest winds over 
the west several hours before they expand into eastern areas.

As the Temperatures continue to warm aloft, expect a likely 
surge to springlike readings Sunday in the immediate wake of the
Cfront, prior to the colder air aloft arriving later in the day
across the Western Mtns. The shallow cool air should mix out 
then there should be a return to seasonal readings for next 
week.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Med range guidance points toward dry weather early next week, 
as high pressure builds across the region. However, model spread
and forecast uncertainty ramps up by the middle of next week 
concerning the track, timing and strength of a fast moving 
shortwave approaching from the midwest. Given when the 
instability is for the storm next midweek, have changed precip 
type to mostly snow.

GFS forecasting potential for another system next weekend, with 
ECMWF developing a weaker coastal low by Sunday. Much uncertainty
through this portion of the forecast so low confidence equals 
low pops.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
VFR conditions early today with overcast high clouds will trend
MVFR to IFR this evening through tonight. Light rain or misty 
drizzle will develop from south to north this afternoon behind
an increasingly moist southerly low level flow. A period of 
steadier/moderate rain is expected overnight into early Sunday 
morning. LLWS is likely late tonight into Sunday morning before
strong post-frontal wind gusts kick in by Sunday afternoon. 

Outlook...

Sun...Scattered rain showers early, then strong FROPA/windshift.
Turning very windy with sfc gusts to 50KT from ~260 degrees. 
Crosswind impacts and moderate to severe turbulence possible 
during takeoff and FAP. MVFR/IFR conditions in snow showers 
likely western 1/3 into Sunday night.

Mon...MVFR/-shsn western 1/3 trending VFR. Windy with sfc gusts
to 50KT from ~290 degrees early then gradually subsiding winds 
west to east into Monday evening. Crosswind impacts and moderate
to severe turbulence possible during takeoff and FAP.

Tue-Wed...VFR/MVFR with chance of light rain/snow showers. 

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
High Wind Watch from Sunday afternoon through Monday afternoon 
for PAZ028-036-037-041-042-046-049>053-056>059-063>066.
High Wind Watch from Sunday morning through Monday afternoon 
for PAZ004>006-010>012-017>019-024>027-033>035-045.

&&

$$
SYNOPSIS...Lambert
NEAR TERM...Lambert
SHORT TERM...Fitzgerald/Lambert
LONG TERM...Lambert/RXR
AVIATION...Steinbugl