Area Forecast Discussion
Issued by NWS State College, PA

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712
FXUS61 KCTP 191538
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1138 AM EDT Thu Apr 19 2018

.SYNOPSIS...
A rather compact but potent low pressure area will move
east from the Ohio Valley and take aim on the Laurel Highlands
and adjacent portions of Central and Southern Pennsylvania
today. Occasional light snow or snow showers will bring a light
accumulation of a coating to around one inch to the higher
terrain of northern and western Pennsylvania today. The ridge
tops of the Laurel Highlands could see locally higher amounts of
around 2 inches. Blustery conditions and unseasonably cold
temperatures will occur Today and Friday. A prolonged period of
dry weather and slowly moderating temperatures will follow for
the upcoming weekend through at least the first part of next
week as a large area of high pressure drifts from the Upper
Midwest to the New England states.

&&

.NEAR TERM /UNTIL 7 PM THIS EVENING/...
Shield of snow/rain under the final piece of upper low finally
moving through and there are NW-SE oriented bands/shsn already
visible in the latest vis shots and radar images. Have tweaked
timing a bit and removed most accums since air is warmer than 32
almost everywhere and the sun should keep things melting as it
falls. Many places will not see any snow mix in - like we just
did here at the office. But the higher elevs will have almost
exclusively snow.

Prev...
Current system affecting the region today displays a much more
detached warm/cold conveyor belt and lighter associated QPF than
was advertised by a host of short range model guidance at this
time Wednesday morning. Additionally, the sfc low is weaker by
2-4 mb and more fragmented while taking a more southern track
across the Virginias (than previously depicted).

These notable changes have impacted (lessened both our snowfall
and wind forecasts). Recently dropped the Winter Weather Advisory
that was in place across our northern tier, since the warm
advection snows likely only accumulated one half of an inch at
best considering borderline temps and just a 60-90 minute period
that afforded the chc for briefly moderate snowfall rates
between 05-08Z.

The main (and quite compact) cold conveyer belt snows falling
across NE Indiana and Northern Ohio ATTM, will slide ESE through
the rest of this morning, and should spread over the Laurel
Highlands and bring a coating to 2 inches of snow accum between
about 12-16Z today. Elsewhere, any steadier precip will be brief
or non-existent today, though much colder temps advecting into
the region within the 850-500 mb layer will steepen lapse rates
and generate scattered-numerous snow showers across the
Mountains of North-Central and NW PA through early this
afternoon with perhaps a coating...up to around an inch on
grassy areas across the higher elevations.

Expect much of the precip to the SE of the Allegheny Plateau to
remain rain through the mid morning hours, but the higher
elevations and over the Plateau will go to wet snow, (or at the
very least a mix).

SLRs will be less than 8:1 = a fairly wet snow. The heaviest
rain (that will exit the SE third of our CWA over the next few
hours) will occur within the preferred lift/thermally indirect
cell associated with the left exit region of the quite strong
upper level jet max (over 100 Kt at 300 MB).

The middle of the road numbers mixing down the wind speeds over
the Laurels and SC Mtns yields some gusts of 25-35kts. This
shouldn`t be nearly enough to necessitate a wind advy.

&&

.SHORT TERM /7 PM THIS EVENING THROUGH 6 AM FRIDAY/...
Temps only rise a deg or two today as CAA and wrap around
clouds make it difficult to take advantage of the mid-April
solar potential.

If they even drop a deg or two, the precip over most of the
area my be snow. But, will still call it mainly a rain/snow mix
for the lower elevations. While some additional accums are
possible Thurs, the main place to have anything stick will be
those that have the snow already on the ground in the morning
and the very highest elevations of the rest of the area.

The gusty wind mentioned before will last much of the day across
the southern third of the area and the north will ramp up to
25-30kt gusts at times. A blustery day for sure. A secondary
push of colder air looks like it will cross the eastern zones
under the aforementioned sharp upper trough, and could make
quite a few showers for places just east of the Susq River. The
temps may even be cold enough on the hill tops of the
Poconos/Schuylkill Co to make snow stick.

Post-frontal/cyclonic flow stratus/strato-cu remain for much of
Thurs PM and a well-mixed lower atmos will keep the temps from
dropping too far. So, the departure from normal mid-April values
is only going to be a negative 5 to 10F.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Shallow stratocu and flurries will persist across the NW half of
the state Thursday night and early Friday, with partly cloudy
skies in the SE. Winds should stay up enough through daybreak
Friday to prevent a frost or freeze in the SE zones, while lows
elsewhere dip into the mid 20s to low 30s.

Friday and beyond, there will be a welcome break of lighter
wind, sunshine and milder temps as a large area of high pressure
moves out of the midwest.

Yet another upper low in this busy pattern looks to drop into
the deep south toward the end of the period. This may spread
some precipitation northward toward our region for the beginning
of next week.

&&

.AVIATION /16Z THURSDAY THROUGH MONDAY/...
Many locations MVFR but were bouncing up and down out of IFR.
Drying air and loss of upper forcing will allow the current
radar echoes and light snow/rain mix to dissipate as it moves
through the rest of the area early this aftn. Expect great
strides in improvement this aftn in the Central and SErn
terminals. Wind should get more gusty, esp at JST and AOO.

Prev...
The area of rain east of the area as of 6 AM. Movement was
about 50 mph to the northeast.

Some fog and real light snow to the west.

12Z TAFs adjusted for the above factors.

Main thing laker today will be gusty winds.

Conditions improve drastically Fri with the arrival of a big
high pressure area which will last through the weekend.

Outlook...

Fri...MVFR cigs nw 1/3; VFR elsewhere.

Sat-Mon...VFR/no sig wx.

&&

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

&&

$$
SYNOPSIS...Lambert
NEAR TERM...Dangelo/Lambert
SHORT TERM...Lambert
LONG TERM...Lambert/Gartner
AVIATION...Dangelo/Martin



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