Area Forecast Discussion
Issued by NWS Binghamton, NY

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FXUS61 KBGM 181957

Area Forecast Discussion
National Weather Service Binghamton NY
257 PM EST Mon Dec 18 2017

Relatively mild temperatures will continue through Tuesday,
along with some spotty light rain or wet snow. Seasonably cold
weather will set in again on Wednesday, along with some lake
effect snow showers and flurries.


130 pm update... Steadier overrunning light precipitation
continues to traverse our far northern zones this afternoon. As
far as precipitation type is concerned, there is enough residual
cold air for snow, possibly with some spotty freezing drizzle,
over Oneida county, as well as far northern Onondaga and Madison
counties. Our expectation is that milder air will gradually push
into these areas as the afternoon wears on, introducing a mix
with light rain. Elsewhere across CNY/NEPA, cloudy and milder
conditions have taken hold, on the other side of the surface
warm front.

By late afternoon/early evening, look for temperatures to range
from the lower 30s in the southern Tug Hill region, to the 35-40
range elsewhere. Overnight, we expect little movement in
temperatures, as low-level warm advection continues. Light rain
and snow will be most persistent again in northern Oneida, with
spotty, very light showers/sprinkles elsewhere.

Tuesday will be a fairly mild day, with a strengthening SW flow
ahead of a clipper type surface low moving across southeastern
Canada, and a surface cold front approaching CNY/NEPA from the
west. Overall, precipitation will be pretty sparse along and
ahead of the cold front, as the better dynamic support is well
north into Canada.

Tuesday night, post frontal passage, colder air will gradually
filter in from the W and NW. As this occurs, a lake-effect snow
band is likely to form off the east end of Lake Ontario. As the
low-level flow veers with time, the lake snow band should drop
southward into Oneida county during the pre-dawn hours. At this
time, parameters do not look favorable for a significant lake-
effect snow event, as the air mass is not that cold, the
moisture not particularly deep, and the nature of the lake band
itself looks transitory.


Wednesday will begin with a 300 degree low-level flow orientation
with 850 mb temperatures running down to -12C to -14C which
leads to a 19-21C Lake temperatures to 850 mb temperature
differential which is decent for lake effect snow in north
central NY. However, the flow will veer pretty quickly and by
afternoon the low- level flow will be more 310-320 degrees with
a subsidence inversion pressing down as upper level confluence
kicks in aloft and forces a surface high pressure system down
across the Great Lakes to the northeast. This will cut off the
lake effect snows quick enough Wednesday to preclude major
accumulations. Right now we have 1-3 in our grids for Wednesday.
Additionally, afternoon highs will be above freezing in some
locations downwind from Lake Ontario hence limiting amounts. At
this time, we are not anticipating advisory amounts. Rest of
forecast area sees mainly mostly cloudy skies with a few snow
showers and flurries in central NY and far northern PA.

Then for Wednesday night, a few flurries will linger mainly in
central NY on a weakening northwest low-level flow as a chilly
high pressure system will drop across the region by late
Wednesday night. This will lead to fair weather and a little
below normal temperatures for mid December for Thursday.

Next low pressure system will reach into the mid-west by
Thursday night with a strong southerly flow and attendant warm
air advection / isentropic upglide over NY and PA. Moisture
will be scarce initially so we expect mainly some flurries in
our northern counties. GFS / Euro and CMC vary in their thermal
profiles with the GFS the warmest and fastest with the warm air
advection and moisture/ precipitation. The Euro and CMC are
slower and colder. This far our we went with more of a CMC /
Euro blend with just a chance for flurries Thursday night as the
main moisture feed is expected to arrive on Friday. This is also
consistent with the superblend.


For Friday, CMC / Euro / GFS all show strong warm and moisture
advection in advance of a deepening storm tracking to our west
through the Great Lakes. Initially, the boundary layer is
expected to be sub-freezing as per model guidance and hence this
could be a messy mixed precipitation event at least during the
onset Friday morning. But, models vary so much in the extent of
the arrival of the moisture / precipitation before surface
layer temperatures warm above freezing. Hence considerably
uncertainty exists as to whether we see any freezing rain. It is
certainly a possibility but will hold off on mentioning in HWO
because we are not confident enough this far out.

Then for Friday night and Saturday we expect milder air with
rain tapering to rain showers as the cold front moves into NY
and PA. More uncertainiy exists as to where this boundary sets
up and the next system which rides up the boundary and affects
our area for Christmas. The CMC / Euro and GFS all have
different scenarios, so went with chance POPs for Saturday
night and Sunday-Monday given timing uncertainities this far
out. We have chance for mainly snow showers but some rain could
mix in during the day.

Christmas day as stated above is even more uncertain. The
GFS would suggest mainly snow with the Euro mixed precipitation
and rain and the CMC rain changing to snow. So for our forecast
we have a chance for rain and snow showers into Christmas day.
It is too far out to be that definitive. Stay tuned...


18z update... At KRME, a mixture of light snow and freezing
drizzle, should evolve more to light rain or drizzle over time,
as milder air builds in. Ceilings will mostly range from MVFR-
fuel alternate, with some IFR possible towards daybreak Tuesday.

At KSYR, light rain/drizzle should taper off later this
afternoon, with VFR going to MVFR for a time later tonight/early

Elsewhere (KITH/KELM/KBGM/KAVP), mostly VFR this afternoon and
evening, could lower to MVFR/fuel alternate later tonight into
Tuesday, before improving to VFR again.

Southerly winds 5-10 kt through tonight, will become SW and
gusty on Tuesday.


Tuesday night-Wednesday...Restrictions possible again in lake
effect snow showers, especially KSYR and KRME.


Friday-Saturday...Restrictions possibly developing again in rain
or mixed precipitation.




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