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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

                            
000
FXUS61 KCTP 171950
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
250 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 tonight. A 
stronger storm will approach for the middle of the week. This
system will have the potential for more in the way of widespread
and heavier precipitation. A third storm is possible next
Sunday. Precipitation with the third system would most likely 
be in the form of rain. Between weather systems, mainly dry 
conditions would prevail.

&&

.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/...
Main change to the package was to take out snow for Tuesday
evening, to fit in better with others. Also ridge still over 
the area and models show little if any QPF into the area before
12Z Wednesday.

For Wed, low pressure lifting northeast across the Great Lakes
will result in some snow, given warm advection. By late morning
and early afternoon, looks like sleet and freezing rain would
mix with the snow. This based on thickness coming up fast, as
the system is weaker and faster than the one we had last week.
Thus did not hit the snow real hard, and did not want to go too
high on ice. This in part due to QPF on NAM across the far south
was looking too high. Other models have the .25 inch line just 
brushing the far south. Hard to see much more than .25 in any 6 
hour period. The NAM had .75 inches across the south in a 6 
hour window.

This event looks like the event last week, most of the precipitation
would be east of the area by Midnight.

For most of the period from Thursday into at least early Saturday,
not a lot going on. I did cut back on POPS and weather where I 
could. Temperatures borderline, so used a mix of rain and snow.

Main question is if a deep low will form and lift across the
lower Great Lakes on Sunday. For now, went close to the
superblend. EC and GFS runs not close. GFS has much weaker 
systems. If EC was to verify, Monday would be the first real
windy day of the late Winter, early Spring season.

&&

.AVIATION /20Z 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...

Tue...No sig wx expected.

Wed...Wintry mix possible. 

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

Fri...Mainly dry. 

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 1 PM EST Monday for PAZ004>006-
010>012-037-041-042.
Winter Weather Advisory until 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/Martin
NEAR TERM...Dangelo/RXR
SHORT TERM...Dangelo/RXR
LONG TERM...Martin
AVIATION...Martin/RXR