Area Forecast Discussion
Issued by NWS Binghamton, NY

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559
FXUS61 KBGM 071150
AFDBGM

Area Forecast Discussion
National Weather Service Binghamton NY
650 AM EST Sat Dec 7 2019

.SYNOPSIS...
Lake effect snow is expected this morning into the early
afternoon hours southeast of Lake Ontario. Otherwise, mainly
dry weather is expected this weekend, followed by rain for
Monday and Tuesday.

&&

.NEAR TERM /THROUGH SUNDAY/...
650 AM Update...
Updated POPs to reflect latest radar trends. Otherwise, no major
changes were made with this update and the previous discussion
remains valid.

Previous Discussion:

Main story for the near term period will be the lake effect snow
showers southeast of Lake Ontario this morning and into the
early afternoon hours. The lake effect coverage has been a bit
more widespread than previously forecast with plenty of forcing
along with a Georgian Bay connection upstream. That being said,
the most persistent band continues to be across portions of
Onondaga, Cayuga, and Madison counties. It is across these areas
that will likely see an additional 1-3 inches of snow, with
generally less than an inch expected in lake effect snow showers
elsewhere.

Any lingering lake effect snow shower activity will likely
taper off during the late morning/early afternoon hours as high
pressure takes control and the flow becomes much lighter. Clouds
will also likely be decreasing throughout the afternoon in
these areas. Further south into much of Northeastern PA, it will
be a partly to mostly sunny day today. Highs will be on the
chilly side though, mainly topping out in the mid to upper 20s
with some lower 30s in portions of the Wyoming Valley and the
Poconos.

A mostly clear and cold night is in store tonight, as
radiational cooling is expected, especially during the first
half of the night. Lows will likely drop to the single digits
across portions of Oneida county with teens expected elsewhere.
Temperatures may begin to rise a bit after midnight as high
pressure begins to move east of the area along with increasing
higher clouds.

Temperatures moderate a bit on Sunday as the high pressure
system moves east of the area, bringing a southerly flow. Highs
are expected to be in the mid 30s to lower 40s. With a
tightening pressure gradient, it will be becoming somewhat
breezy during the afternoon hours. Otherwise, expecting a partly
sunny day with increasing clouds late in the day ahead of the
next system.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
415 AM update...
Temperatures ascend and descend in the short term period, which
will be wet from both rain and snowmelt. Main issues are
potential for elevated streamflows late Monday into Tuesday, and
also details of lingering rain mixing with snow late Tuesday-
Tuesday night as cold air starts to move back into the region.

We start in the upper 20s to upper 30s Sunday evening, coldest
east of Interstate 81. Temperatures will slowly rise overnight,
and it will be a race against time as to whether all areas will
be above freezing when rain starts to develop early Monday.
Northern Oneida County, and perhaps a few spots in the
Catskills, could very briefly have a wintry mix of freezing
rain-sleet-snow if precipitation arrives early enough. The more
probable scenario at this time appears to be all rain as
temperatures surge into the 40s by Monday afternoon. A more
typical ice threat would include high pressure New England with
cold air damming down the Appalachians; but in this case the
high will be due east and well offshore, thus a strong southerly
return flow between it and low pressure advancing through the
Midwest-Southwestern Great Lakes.

In the bigger picture, a broad upper trough will be digging
across the Central U.S. with deep southwest flow extending from
the western Gulf of Mexico to the Midatlantic states. In
addition to causing warmer temperatures, moisture will
increasingly be brought up with rain developing Monday and
lasting through Tuesday. There is some potential for a
combination of rain and snowmelt to cause elevated stream
levels and nuisance poor drainage ponding, especially upper
Susquehanna-upper Delaware Basins and Poconos-southern Catskills
areas. However, balance of model guidance has been shunting
heavier rains a bit further southeast. We could still see up to
an inch of rain still possible in those areas; most of it
Monday-Monday night. There is also an inch or more of liquid
snow water equivalent that is contained in the snow pack there
especially higher elevations, and very mild temperatures as well
as dewpoints surging through the 40s late Monday through midday
Tuesday will be capable of releasing a chunk of that water.
Model ensembles continue to indicate a few river points perhaps
reaching action stage, but odds for true river flooding still
appear quite low. This will continue to be monitored; at a
minimum we can expect ponding in poor drainage areas, and some
healthy rises in streams.

Deepening low pressure will shoot from lower Michigan Monday
night into southern Quebec Tuesday, with a trailing cold front
dragging west-northwest to east-southeast across our region
midday through early evening. However, moist southwest flow
will still exist aloft, with right entrance region of a strong
upper jet causing forced ascent behind the front. Thus for the
precipitation that lingers, we can expect a transition from rain
to snow late Tuesday through Tuesday night. There is some
potential for a light snow accumulation Tuesday night, but we
will better be able to sort that out with time. Temperatures
first thing Tuesday will be very mild in the 40s to lower 50s,
but we can anticipate a drop behind the front Tuesday afternoon-
evening, for eventual lows of mainly 20s by dawn Wednesday.

&&

.LONG TERM /WEDNESDAY THROUGH FRIDAY/...
430 AM Update...
We return to an Arctic regime later this week.

Strong cold air advection will begin Tuesday night which
continues right through Wednesday night. 850mb temperatures
start Wednesday morning around minus-10 Celsius but further
plummet to between minus-15 and minus-20 Celsius by Wednesday
evening, which persists into Thursday. This will indeed be a
cold air mass with highs of lower 20s-lower 30s Wednesday and
then only upper teens-upper 20s Thursday as the Arctic high
passes overhead. Overnight lows for Wednesday night-Thursday
night, will be mainly teens but perhaps some single digits.

With low level flow veering westerly Wednesday to eventually
northwesterly Wednesday night-early Thursday, we can anticipate
lake effect snow showers for much of the region with perhaps
more significant accumulations occurring north of the New York
Thruway. The air mass appears quite supportive of lake snows
with the dendritic growth zone down in the heart of the mixed
boundary layer. This will be figured out with more certainty in
coming days.

We get into a moderating return flow on the back side of the
departing high Friday, with dry weather and highs forecast back
into the upper 20s-mid 30s.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
Lake effect snow showers and clouds will be the main concern
this morning into the early afternoon. Only two terminals to
likely remain VFR the entire period will be at KELM and KAVP.
Otherwise, snow showers will bring occasional MVFR ceilings and
visibilities this morning to KSYR, KRME, KITH, and KRME. Brief
Fuel Alternate restrictions in localized heavier snow showers
aren`t out of the question, especially at KSYR and KRME.
Conditions likely improve to VFR at all terminals this afternoon
and through tonight.

Winds today will be northwesterly at less than 10 knots, before
becoming more south-southeasterly this evening/tonight.

Outlook...
Sunday...VFR.

Monday and Tuesday...Restrictions likely with a broad area of
rain across the region.

Wednesday...Restrictions possible in lingering snow showers.

&&

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

&&

$$
SYNOPSIS...BJG
NEAR TERM...BJG
SHORT TERM...MDP
LONG TERM...MDP
AVIATION...BJG



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