NWS Forecast Discussion

000
FXUS61 KBGM 111148
AFDBGM

Area Forecast Discussion
National Weather Service Binghamton NY
648 AM EST Mon Dec 11 2017

.SYNOPSIS...
After scattered morning snow showers and flurries, things will
be fairly quiet until a clipper system quickly moves through
tonight into early Tuesday with accumulating snow. Lake effect
snow will follow for Tuesday afternoon through Wednesday night
in Central New York and perhaps some of the Northern Tier of
Pennsylvania, as Arctic air descends across the region.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
645 AM Update...
We were able to drop the winter weather advisory earlier, that
had been in effect for Northern Oneida, since snowfall
rates/banding were already significantly diminishing. That being
said, around an inch or so of fluff will be possible from the
last vestiges of lake effect this morning.

Clipper system tonight-early Tuesday, plus the Arctic air and
lake effect snow that will follow, are the main forecast
concerns in the big picture. For details on that please refer
to the short term portion of this area forecast discussion.

Previous discussion...
Lake Ontario band shifted north of the area much of yesterday,
but with approach of a shallow cold front it is now reorienting
as of 3 AM. It will bodily carry through northern Oneida county
during the next several hours, likely reducing visibility to
about a mile while dropping another quick 1 to 2 inches north of
the NY Thruway. We will allow Winter Weather Advisory to
continue up to the scheduled expiration of 7 AM this morning. As
winds veer northwesterly behind the front, inversion heights
will also rapidly drop to below the dendritic growth zone, which
along with drier air will allow the lake effect to transition
to multi-band snow showers and flurries after dawn this morning,
before ending around midday. So south of the Thruway to about
as far as Moravia-Cortland-Pharsalia-Morrisville-Waterville,
accumulations this morning should be limited to a fluffy dusting
to around an inch. Elsewhere just a few flurries are expected
as the weak front passes; many locations especially in Northeast
PA will see nothing at all due to the amount of dry air.

Though there will be a gradual decrease in lake clouds, high
thin clouds will quickly stream in ahead of the approaching
clipper, and then thicken with time. This will hold highs back
to generally in the mid 20s to mid 30s range.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY/...
400 AM Update...The highly advertised clipper low will
strengthen as it tracks across the Great Lakes and into New
York tonight and Tuesday. Light snow will break out in
isentropic lift regime over CNY and NEPA by late evening with
best forcing across NY portion of forecast area. Snow picks up
with time heading into the Tuesday commute. Warm advection
appears to be split into lift and warming of the boundary layer
enough to significantly affect snow-liquid ratios and surface
temps tomorrow morning. Arctic front with falling temperatures
arrives late afternoon.

The favorable dendrite crystal layer rises tonight to about
10K-13K feet with relatively mild air beneath. Dry slot also
noted to come into play as strong jetlet rounds base of upper
low Tuesday. Snow totals will not be easy with this one due to
the above factors as there will likely be insufficient flake
production, some stoppage of precip at times, and low level
warming to melt what falls, or even provide some liquid flakes
in some of the warmest locales. Looking for a quick 1-3"/2-4"
accumulation in a S-N gradient overnight and nominal accums on
Tuesday with some melting. Given this uncertainty, have held off
on issuing winter advisories across the Southern Tier and NEPA
pending further review.

We have issued a Winter Storm Watch through Wednesday across
the northern zones where confidence in several inches is
highest. It looks to be just a tad colder overall, coupled with
topographic enhancement along the Tug Hill and Mohawk Valley.
Synoptic and hi-resolution models were simulating this with a
QPF bullseye in this area. In addition...a good set up for LES
along a 290-310 flow develops later Tuesday night and Wednesday
post Arctic frontal passage. Lapse rates beneath inversion layer
appear stout with limited shear and good support from synoptic
moisture. Thus, multi-single band hybrid lake effect/enhancement
should produce healthy squalls and accumulations through
Wednesday for the Syracuse area and hilltowns to the south. A
good portion of the area southeast of Lake Ontario is likely to
see a bunch of snow by Wednesday afternoon. Watch (and/or
Warnings) may need to be expanded slightly depending on
confidence of inland extent to snow plumes.

Turning much colder by Wednesday with highs struggling in the
teens to lower 20s.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
400 AM Update...No significant changes to medium range with
long wave pattern remaining in a broad trof and models
consistent with 12Z runs.

Previous discussion...
Flow becomes more westerly and relaxes on Thursday so snow
showers will taper off. However, unsettled weather will continue
through Friday with trofiness aloft, a clipper moving into the
Great Lakes, and systems running up the coast to our east.
Confidence in forecast is low to moderate until Friday when
global models diverge quite a bit on positioning and timing of
disturbances diving around the base of the trof and interacting
with the front along the coastal plain. Chance PoPs during this
time and some moderation of temperatures with flatter flow and
slight warm advection. Temperatures look to potentially warm
above freezing into the mid-30s to lower 40s by next Sunday, as
a storm system passes by well to our north. This system will
bring chances for rain and snow showers, and perhaps some mixed
precipitation.

&&

.AVIATION /12Z MONDAY THROUGH FRIDAY/...
Lake effect snow is winding down this morning, but between
12Z-15Z there will still be times of 1-4 mile visibility for
KRME-KSYR. Brief high end MVFR ceiling and a light flurry will
still initially be around KBGM-KITH, otherwise all terminals
will go to VFR late morning through early evening. Wind is
veering to west-northwest but less than 10 knots, becoming
variable late afternoon to southeast tonight. With this busy
pattern, a clipper system will already start moving across the
region from 03Z onward with IFR to fuel alternate required
conditions becoming likely through dawn Tuesday.

Outlook...

Tuesday morning...Lingering restrictions as a clipper system
finishes moving through the region.

Tuesday afternoon through Wednesday night...Gusty snow showers
and associated restrictions, especially NY terminals.

Thursday through Friday...Still a chance for snow showers and
intermittent restrictions.

&&

.BGM WATCHES/WARNINGS/ADVISORIES...
PA...None.
NY...Winter Storm Watch from this evening through Wednesday
     afternoon for NYZ009-018-036-037.

&&

$$
SYNOPSIS...MDP
NEAR TERM...MDP
SHORT TERM...JAB
LONG TERM...JAB/MJM
AVIATION...MDP

NWS BGM Office Area Forecast Discussion