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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KBGM 121449
AFDBGM

Area Forecast Discussion
National Weather Service Binghamton NY
949 AM EST Thu Dec 12 2019

.SYNOPSIS...
Lake effect snow showers north of the New York Thruway will
gradually taper off through mid morning. Otherwise, high
pressure will provide a period of dry weather for the region
through at least Friday morning. Low pressure is expected to
organize as it tracks up the eastern seaboard and bring rain to
the area Friday night and Saturday. Rain may briefly end as snow
late Saturday as the storm systems pulls away from the area.
Another round of lake-effect snow showers is likely for the
second half of the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...

Only minor adjustments to the forecast with the mid-morning
update. Forecast discussion below on track.

4 AM Update...
Overnight surface analysis shows a 1039 mb surface high centered to
our south across NE MD-SE PA. Westerly flow around the high will
subside this morning as the ridge axis that extends northward moves
into the area.

Latest GOES-16 satellite imagery shows a lake-effect cloud band
extended eastward from Lake Ontario into our far northern zones of C
NY (north of the NY Thruway). Despite poor radar coverage with KTYX
radar down and other nearby radars overshooting the low-topped
convection embedded within the LES band, New York State Mesonet
(NYSM) webcams show light snow continuing to fall overnight across
western and northern Oneida Co. (likely extending a bit southward
into far northern Onondaga and Madison Counties. Snow depth readings
at these same NYSM sites in far N/W Oneida Co. estimate 2-3" of
snowfall since yesterday afternoon. An additional 1" or so is
possible early this morning before the LES activity dissipate by
late morning.

Outside of the narrow lake-effect cloud band, subsidence under the
high will allow for a sunny start to the day for most locations. Mid
and high clouds will overspread the area from the west later this
morning and afternoon as mid-level WAA and upper-jet dynamics arrive
ahead of a weak disturbance. Forecast highs ranging from the upper
20s across the higher elevations of CNY to mid 30s in the Wyoming
Valley are 4-8 degrees below normal.

The center of the surface high shifts off the New England coast
tonight although models do show the ridge axis noses southwestward
along the eastern seaboard (indicative of cold-air damming along
eastern side of the Appalachians). Southerly return flow aloft
around the offshore ridge will continue to advect warmer air
northward up the eastern CONUS. There are indications that a marine
stratus deck develops along the Mid-Atlantic coast and expands
northeastward into NE PA and the W Catskills by early morning. The
southerly winds should keep the boundary layer decently mixed and
prevent temperatures from bottoming out. Nonetheless, it will still
be a seasonably cold night with lows in the lower to mid 20s
(pockets of teens in the western Catskills and southern Tug Hill
Plateau).

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
645 AM Update...
Quick update to account for the gradual northward retreat and
overall weakening of the lake-effect snow band east of Lake
Ontario. Additional snowfall amounts this morning in N/W
portions of Oneida Co. should be under a half inch. Also updated
the temperatures with a few sites in the Finger Lakes region
(including ITH and NO3) dropping into the single digits.


4 AM Update...
A complex storm system will initially be comprised of an area of low
pressure over the Central Plains and another low centered along the
northern Gulf-of-Mexico coast on Friday. A secondary low is expected
to develop along a warm front/coastal front boundary along the
Southeast Coast Friday night. Models still show this secondary
coastal low deepening rather quickly as it lifts northward up the
Mid-Atlantic coast early Saturday and through the upstate NY late
Saturday.

The track of the low still looks to be far enough inland to yield a
mainly rain event for our forecast area. However, the leading edge
of precipitation could potentially produce isolated pockets of
freezing mainly across the higher elevations of the Poconos and
western Catskills. This icing potential would be very brief (though
models tend to erode the shallow cold wedge near the surface too
fast in cold-air damming setups) and contingent on the precip
arriving early enough in the day (late morning, early afternoon at
the latest) for the residual cold air to still be in place.

The steadiest rain looks to overspread the area late Saturday night
and continue into Sunday morning. Based on the current QPF ranging
between 0.75" and 1.25", not expecting much in the way of flooding
issues with this event aside from localized poor drainage
issues. Depending on the exact track of the low and how quickly
wrap around precip shuts off, rain may end as snow once the
colder air moves in on the backside of the system. There is
uncertainty with the timing of a changeover but it could
conceivably occur as early as Saturday afternoon across our far
western zones.

Models generally agree that the low will rapidly deepen while
it passes by the area and moves roughly down the Saint Lawrence
Seaway Saturday night into Sunday. The broad cyclonic wind field
around it will thus enhance, which along with the steep
boundary layer lapse rates of wrap-around cold air advection,
will result in a brisk day Sunday. Westerly winds appear likely
to gust frequently in the 25-35 mph range, with isolated 40 mph
gusts not totally out of the question especially for the
northern zones.

After lows of around 30 to mid 30s Saturday night, temperatures
move little Sunday under continued gusty cold air advection,
resulting in highs of lower 30s-near 40. Steadier precipitation
will diminish to scattered showers as Sunday carries on, before
ending as the moisture lifts south to north. Type will be
heavily reliant on elevation - mainly snow showers in high
terrain and mainly rain showers in the valleys. Total snow
Saturday night through Sunday will be pretty nominal for most
locations, though northern Oneida County could end up with a few
to several inches. Additional snow, of the lake effect variety,
could occur north of the New York Thruway Sunday night as 850mb
temperatures briefly dip into low to mid teens Celsius below
zero in west or west-northwest flow. Lows Sunday night will be
mainly 20s, except for mid teens in northern Oneida County.

&&

.LONG TERM /MONDAY THROUGH WEDNESDAY/...
4 AM Update...
With our active pattern continuing unabated, a brief break much
of Monday, is likely to give away to another system moving
southwest to northeast through the general area late Monday into
Tuesday. All models have the system yet differ in whether
tracking the primary low just south of the area as per the
ECMWF, or further northwest like the GFS-Canadian models.
However, even the relatively cooler ECMWF manages to get above
freezing at 850mb for a sizable chunk of the area.

A snow to wintry mix scenario is anticipated for Monday night
into Tuesday. There could be some snow and/or ice accumulations
with this, but things could easily change considering it is
quite a ways out; we will better figure out the details in
coming days. It could quickly transition to rain with a
northwest track, or remain mostly snow-freezing rain mix with
southeastern one. However it works out, a piece of Arctic air is
projected to dip behind the system into our area as we head
into Midweek. As usual, this scenario could produce lake effect
snow.

&&

.AVIATION /15Z THURSDAY THROUGH MONDAY/...
Lake-effect snow showers have finally pushed north of RME.
However, forecast soundings show MVFR CIGs lingering at RME
through the late morning. Elsewhere, VFR is expected today
with mid- and high-level clouds streaming into the area. Winds
vary between NW and SW early this morning but speeds continue to
decrease (generally under 7 kt) as the pressure gradient
relaxes. Winds back more out of the S this afternoon with
speeds below 10 kt.

Mainly VFR tonight with a strengthening southerly return flow.
Winds at the surface look to increase to 8-13 kt this evening
with occasional gusts near 20 kt favored at our NY terminals.
Forecast soundings show a strengthening SW low-level jet to near
50 kt at 2 kft AGL for our western-most terminals (SYR, ITH, and
ELM). LLWS was added with the 12Z TAFs for these western
terminals.

Outlook...
Friday...Low clouds with CIGs borderline IFR-MVFR criteria may
try to sneak into our S/E terminals (AVP-BGM-ELM) just before
sunrise Friday morning. These low clouds may expand farther N/W
throughout the day with rain moving in late.

Friday night and Saturday...Flight restrictions expected in
periods of rain.

Saturday evening through Sunday...Continued flight restrictions
into Saturday night. Rain may changeover to snow from W-E before
it ends Saturday night. Gradual improvement in CIGs expected on
Sunday as the steady snow ends. However, lake-effect snow
showers will result in more localized restrictions, especially
for NY terminals. NW winds will be breezy.

Monday...VFR.

&&

.BGM WATCHES/WARNINGS/ADVISORIES...
PA...None.
NY...None.

&&

$$
SYNOPSIS...JRK
NEAR TERM...JRK/MWG
SHORT TERM...JRK/MDP
LONG TERM...BJG/MDP
AVIATION...JRK