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Area forecast discussion
National Weather Service Buffalo New York
515 PM EST Wed Dec 11 2019

Synopsis...
a lake effect snow band will move south through this evening,
with snow ending late this evening east of Lake Erie, and
Thursday morning off Lake Ontario. High pressure will then bring
a return to dry weather later Thursday through Friday. Low
pressure moving northward along the East Coast will then bring
rain and warmer temperatures to the region Friday night through
Saturday, with rain changing back to snow Sunday as colder air
moves back into the area.

&&

Near term /through Thursday/...
the Main Lake effect band east of Lake Erie continues to move
east-southeast and will lose its connection fairly quickly this evening.
Until this happens, impressive snow rates of 1-3"/hr are
possible, although most areas will only see snow for about an
hour or so. There is another weaker band with some upstream
ties that will move east-southeast across far wny, but impacts will be low.

Over Lake Ontario, one band with an upstream connection to Lake
Erie is moving fairly quickly into the Tug Hill, while the Main
Lake Ontario band is finally in full bloom near kart.

In addition to lake snow, many areas close to the lake bands are
experiencing west winds gusting to ~40 miles per hour with blowing and some
drifting snow. There have been a few instances of thundersnow.
This type of event is probably over downwind of Lake Erie,
although wouldn't be surprised to see some strikes near the wind
towers east over the Tug Hill.

Equilibrium levels to 12k feet and strong winds will allow lake
effect bands to extend quite far inland off Lake Erie, with
showers extending into the mid/upper Genesee Valley and western Finger
Lakes this Evening.

Lake effect snow off Lake Erie will taper off rather quickly
across the western southern tier, ending by late evening as
drier air builds in and equilibrium levels lower behind the
shortwave.

Significant lake effect snow will continue off Lake Ontario.
The initial band will drop southward, moving across Oswego and
Lewis counties through early evening. This may be followed by a
brief lull. A band of lake effect snow should then re-develop
near the southeast corner of the lake this evening. This band
will settle south across Oswego County as boundary layer flow
becomes west-northwest. Unlike Lake Erie, this band will last longer with a
more favorable environment over Lake Ontario through early
Thursday morning. Moisture will be limited, so this band is
expected to be narrow, but there will be a brief period where
winds drop off enough for a land breeze convergence boundary to
develop late tonight before winds shift to the south and shear
increases Thursday morning. This band may briefly meander into
northern Cayuga County, with its intensity still uncertain.
Snowfall rates of 1-2 inches per hour will be common, with a
general 3-5 inches of snow expected. The Tug Hill may see up to
6 inches as the strongest forcing interacts with upslope flow.
Oswego County may also see up to 6 inches if the overnight band
remains in one location long enough.

Thursday, winds will back as surface high pressure passes just to
our South. Lake effect snow off Lake Ontario will shrink across
the lake with weakening winds, before sliding north and tapering
off through early afternoon. Any additional accumulation will be
modest, maybe an inch or so along and to the west of I-81. A
few flurries are possible early Thursday near Buffalo on a
southwest flow. Outside of lake effect snow there will be quite
a bit of sunshine Thursday morning, but cloud cover will
increase as mid-level moisture overspreads the region.
Temperatures will remain on the cool side with highs in the
upper 20s to lower 30s.

&&

Short term /Thursday night through Sunday/...
a 1040mb high will move off the New England coast Thursday night. A
southerly flow will persist across the region through Friday with
afternoon highs reaching the low 40s. Coastal high pressure will
extend southwestward across coastal New England and the mid-Atlantic
during this time. Dry conditions will remain across western and
north central New York through Friday.

Mid-level level ridging moves off the East Coast Friday night. A
deepening trough will track across the Mississippi Valley overnight
while low pressure develops across the southeast U.S. And tracks
north into the mid-Atlantic region. Initially, the northern stream
will develop low pressure across the mid-west while the southern
stream develops low pressure across the Gulf Coast states. As the
trough tracks eastward overnight, these two systems will phase into
a coastal low on Saturday. Strong moisture advection will occur as
Gulf of Mexico and Atlantic Ocean moisture get wrapped up along the
East Coast Saturday.

As moisture moves into western New York Friday night, most places should
be above freezing and rain is expected. However, a few places across
the western southern tier may fall below freezing temperatures in
the early evening and may lead to a wintry mix for a few hours.
Similarly, temperatures will have a longer time to fall east of Lake
Ontario prior to the onset of precipitation which may produce a
period of a wintry mix. Temperatures will slowly climb overnight and
into Saturday morning because of the strong warm air advection and
any wintry mix should change over to rain by Saturday morning. Highs
in the low to mid 40s expected Saturday.

The model consensus is for low pressure to track from central PA to
northern Vermont Saturday to Saturday night. As the low passes to
the east and northeast, cold air advection will move into western
and north central New York. This system is moisture laden so as colder air
moves into the region, snow showers are likely from west to east
through Saturday night. Minor Lake enhancement expected through
Saturday night as lake induced instability is lacking with 850mb
temperatures only falling to around -6c by Sunday morning. An inch
or two of snowfall accumulation is possible mainly at higher
elevations east of Lake Erie and Lake Ontario.

&&

Long term /Sunday night through Wednesday/...
Sunday and Sunday night deep low pressure will push from the lower
Saint Lawrence valley across Labrador and then out to sea...while
high pressure over the northern plains states steadily builds east
across the Great Lakes. In between these two systems...a gradually
weakening and drying westerly to west-northwesterly flow of colder
air will persist across our region. The cold advection regime will
result in morning highs in the mid to upper 30s Sunday giving way
to slowly falling readings through the remainder of Sunday and Sunday
night...when lows will settle into the teens across the north country
and the lower to mid 20s elsewhere. Meanwhile...initially breezy to
windy conditions on Sunday (worst along the eastern and southeastern
shores of both lakes where winds could gust to 35-40 mph) will give
way to progressively calmer conditions through Sunday night as the
surface ridge builds into our region.

In terms of precipitation...even though the bulk of the synoptic
precipitation will be over by the start of this period...ongoing
upslope flow and deep moisture will still maintain numerous to
widespread snow showers east/east-southeast of the lakes Sunday
morning...with these then steadily diminishing Sunday afternoon
and night as our airmass steadily dries out and inversion heights
lower. Similarly...much more scattered mixed rain and snow showers
elsewhere on Sunday will also come to an end Sunday night. While
it will indeed be breezy to windy on Sunday...have pulled the
previous mention of blowing snow from the forecast as temperatures
both at the surface and aloft suggest a wetter snow that will be more
difficult to effectively blow around.

On Monday the surface ridge will slowly drift from New York state
into New England. Apart from some dying widely scattered light snow
showers/flurries southeast of Lake Ontario early on...this should
result in a dry day...with partly sunny skies initially giving way
to increasing clouds across western New York out ahead of the next
system. Meanwhile daytime highs should be a bit below average...
with readings ranging from the upper 20s across the north country
to the lower to mid 30s elsewhere.

Monday night through Tuesday night the medium range guidance continues
to exhibit significant discrepancies with the track of the next low
pressure system. The latest GFS remains a northern outlier and tracks a
deepening low directly across lakes Erie and Ontario...which would
favor a mixed precipitation event along followed by the potential for
some gusty winds behind its trailing cold front...though at this point
the low track appears to lie too close to our region to support a true
high wind event. Meanwhile the Gem and European model (ecmwf) remain much further south
with the low track and support a potential for some snow across our
region...with the extent of this potential dependent upon the exact
track of the low. For now have continued to favor the more realistic-
looking latter Camp of models...with a general chance of snow and near
to slightly below average temperatures indicated for this 36-hour
period.

Following the passage of this next system...a colder west to west-
northwesterly flow looks to follow for Wednesday...supporting highs
back in the 20s again along with a chance of snow showers east and
east-southeast of the lakes.

&&

Aviation /22z Wednesday through Monday/...
Lake effect snow will continue to impact kart through about 00z
and to a lesser extent kjhw. Other taf sites, kiag, kbuf, and
kroc may see very brief reductions toward IFR/MVFR before
quickly bouncing back to VFR a narrow band or two crosses the
region from northwest to southeast.

Later this evening, expect mainly VFR conditions with lake
snows focusing east of the Lakes. Lake snows will taper off
late tonight off Lake Erie and Thursday morning off Lake
Ontario. Expect mainly VFR flight conditions late tonight
through Thursday taf sites. A brief period of MVFR conditions is
possible at kart/kiag/kbuf Thursday morning when the remnant
lake effect clouds (and maybe a snow shower) move through these
terminals.

Outlook...

Thursday night...VFR.
Friday...VFR.
Saturday...MVFR. Rain likely.
Sunday...areas of MVFR/IFR in snow showers, especially
southeast of the lakes.
Monday...VFR.

&&

Marine...
a cold airmass will continue to spread bands of lake effect snow
east across the lakes this evening. A brief period of marginal
35 kt gales will accompany the cold front on both lakes. Winds
will quickly diminish tonight as the pressure gradient relaxes
across the eastern Great Lakes.

&&

Tides/coastal flooding...
there will be a period of low end gale force winds this evening
on Lake Ontario. The strong onshore winds, high wave action,
and High Lake levels will bring an increased risk of Lakeshore
flooding along the Lake Ontario shore at the east end of the
Lake. A Lakeshore Flood Warning remains in effect for
Jefferson, Oswego, and northern Cayuga counties through
tonight. This event will not be as significant as the Halloween
night Lakeshore flooding, but still may be high enough to result
in some flooding in flood prone areas and more shoreline
erosion.

&&

Buf watches/warnings/advisories...
New York...Lakeshore Flood Warning until 4 am EST Thursday for nyz005>007.
Winter Weather Advisory until 1 am EST Thursday for nyz007-008-
019-020.
Winter Weather Advisory until 4 am EST Thursday for nyz006.
Winter Weather Advisory until 8 PM EST this evening for nyz012-
085.
Lakeshore flood advisory until 7 PM EST this evening for
nyz010-019-085.
Marine...Small Craft Advisory until 10 PM EST this evening for lez020.
Gale Warning until 7 PM EST this evening for lez040-041.
Small Craft Advisory until 10 PM EST this evening for
loz030.
Small Craft Advisory until 7 am EST Thursday for loz042-
043.
Gale Warning until 1 am EST Thursday for loz044-045-
063>065.
Gale Warning until 10 PM EST this evening for loz062.
Small Craft Advisory until 10 PM EST this evening for
slz022-024.

&&

$$

Synopsis...apffel/Hitchcock
near term...apffel
short term...hsk

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