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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

                            
000
FXUS61 KCTP 171803
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
103 PM EST Sun Feb 17 2019

.SYNOPSIS...
A fast flow aloft will keep the weather active through the week.
A weak disturbance will move across the region later Sunday and
Sunday night. A stronger storm will approach for the middle of 
next week. A third storm is possible at the end of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
High pressure retreating very quickly to the NE today as low 
pressure moves just as quickly up the Ohio Valley. Warm 
advection will trigger a wintry mix of precip to develop over 
the west late in the day. Continuity is high with the forecast, 
so confidence is fairly high. The precip type is the trickiest
part. But, that has also been fairly consistent in model progs 
the last few days. Maxes today will be highest over the east, 
where the clouds arrive latest. Almost no guidance has precip 
any farther east than route 219 by 21Z. But it does spread over 
the area quickly this evening.

Snow will be the initial precip type in most places, but it
could turn to sleet quickly everywhere south of I-80. The snow
will last longest over the nrn mtns. The temps warm aloft as the
low moves into the CWA, and most places will turn to freezing 
rain/drizzle after the best lift moves off to the north
(mid/late evening). SLRs will be 12-13:1 at first over the 
north, but drop below 10:1 by midnight. The QPF is not very 
heavy, but the duration of the snow in the north will likely 
lead to 2-4 inches there by the middle of the night. Elsewhere, 
the sleet will keep numbers down, but will still make a mess -
especially on untreated surfaces. The threat of FZRA/DZ is 
highest over the Laurels. But, again, the QPF is <= 0.25", so 
ice accums will likely not get into warning amounts since not 
all of it will be FZRA.

Temps remain very constant overnight...near freezing in much of
the area south of I-80. The Laurels could get >32F later in the
storm, but the E/SE flow in place for most of the night doesn't
give up the cold air very easily. 

&&

.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
As the low moves into NY, a small low may form over the 
DelMarVA, and briefly hang precip up in the SE. But, temps will 
also be warming after daybreak, and much of the area will be out
of the threat of FZDZ by 8-10 am. The temps will get cold 
enough over the NW half to make anything left over into snow 
showers. The downslope in the wake of the low will make it mild 
in the SE, and help to break up the clouds there. The west wind 
could gust to 30 mph in the southern tier in the afternoon.

Surface high pressure expands into the region Monday night. Once
breezy winds die down, temps will fall into the single digits
north of I-80, and in the teens/20s elsewhere. 

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Monday night and Tuesday, expansive surface high pressure will 
expand from central/eastern Canada into the northeastern states,
with dry and seasonably chilly weather.

Current indications still are that another wintry mix event will
affect the Commonwealth from later Tuesday night through
Wednesday, with a snow to sleet/freezing rain to perhaps rain
transition anticipated. Stay tuned for the latest forecasts, as
specific details become clearer over time. 

Overall, our weather should dry out Thursday and Friday, as the
previous system lifts away to our northeast. Cyclonic W-NW flow
could bring some light rain or snow showers, but they look
inconsequential at this early juncture. 

Current model consensus points to a deepening storm system 
lifting northward through the Great Lakes/upper Midwestern 
states. Such a storm track would be likely to ultimately bring 
rain and milder temperatures. However, an initial wintry mix 
still appears possible prior to that. Once again, uncertainty is
high this far out, so stay tuned for later details.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
Expect deteriorating conditions this afternoon and evening, as 
an approaching storm spreads a light wintry mix and lowering 
cigs from SW to NE across the region. Latest model output 
supports widespread IFR conditions by late evening and 
continuing at least past sunrise Monday morning.

Flow turns WNW on Mon, bringing improving conditions to the SE
and lingering MVFR to the western higher terrain in light snow
showers. Winds increase to 10-20 mph with gusts to 30 mph over
the southern tier and Susq Valley.


Outlook...

Mon...AM low cigs possible. 

Tue...No sig wx expected.

Wed...Wintry mix possible. 

Thu...AM wintry mix/low cigs possible.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 4 PM this afternoon to 1 PM EST 
Monday for PAZ004>006-010>012-037-041-042.
Winter Weather Advisory from 4 PM this afternoon to 10 AM EST 
Monday for PAZ017>019-045-046.
Winter Weather Advisory from 7 PM this evening to 10 AM EST 
Monday for PAZ027-028-049>053-056>059-063>066.
Winter Weather Advisory until 10 AM EST Monday for PAZ024>026-
033>036.

&&

$$
SYNOPSIS...Dangelo
NEAR TERM...Dangelo/RXR
SHORT TERM...Dangelo/RXR
LONG TERM...Jurewicz
AVIATION...RXR