Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 131540

Area Forecast Discussion
National Weather Service Buffalo NY
1040 AM EST Tue Nov 13 2018

Cold air will filter into the region today behind a system
that`s moving northeast along the New England Coastline. This
will result in a few bands of lake effect snow downwind of Lake
Erie and Lake Ontario on a northwest flow. A stronger band setup
is likely southeast of Lake Ontario late tonight into Wednesday,
while the rest of Western New York sees dry weather. The next
system will begin to impact the region late Thursday and last
through Friday.


A surface low is moving moving northeast toward the New England
coast this morning with most of the precipitation shield already
east of Western NY. This will result in a period of quiet
weather for the region while colder air slowly moves in from the
west along with an upper level trough. This will result in an
increasing chance for multi-band lake effect rain and snow
showers toward the afternoon but with little overall impact.

Tonight, temperatures at 850 hPa will drop from around -10C
this evening to around -15C by daybreak. This will steepen lapse
rates while equilibrium levels increase over the still warm
eastern Great Lakes. Initially, lake effect snow will be light
and multi banded in structure without a focusing mechanism.
But as colder air builds across the lakes, a weak lake
aggregate trough will develop and help to form a low level
convergent field that should bring a singular band of snow
southeast of Lake Ontario. A winter storm watch for lake effect
snow is in effect. While a band may form first over the Tug
Hill, it should reform or move to the south toward Wayne,
Northern Cayuga, and Oswego counties.

Temperatures today will remain mostly in the 30s. Cold air
advection tonight will allow temperatures to dip to the 20s.
East of Lake Ontario, some clearing is likely with lows in the


A band of moderate to potentially heavy lake effect will likely be
ongoing Wednesday morning targeting Wayne, Northern Cayuga and
Oswego counties. Pattern recognition and profiles definitely support
this idea through at least midday. Good synoptic moisture
contribution within a growing lake induced equilibrium level
exceeding 10k feet. Omega is pegged well within the dendritic
growth layer. Most higher resolution guidance suggesting an
upstream connection only helping the snow producing cause.
There could be a narrow window of high snowfall rates of 2+
inches per hour during the morning. The duration of this window
still a bit uncertain as drier air will build in and start to
diminish the snows through the afternoon and evening hours.
Current thinking is for 5-10 inch totals within this area with
much of the snow falling during the morning, but potentially
lasting longer.

Off Lake Erie, simply not nearly as impressive with more limited
background moisture. The northwest flow will produce multibanded
lake effect snows downwind of the lake with accumulations of a few
inches before the drier air starts building in with diminishing
activity by midday.

Any lingering lake snow southeast of Lake Ontario will end Wednesday
night as high pressure slides across the region. The high will
maintain dry weather through Thursday morning.

A compact, closed southern stream circulation will then lift
out of the lower Mississippi Valley later Thursday interacting
with northern stream energy diving southeast from the upper
Midwest. These two features will phase and result in east coast
cyclogenesis by Friday. Ahead of this, with good divergence
aloft and increasingly supportive jet dynamics, enhanced large-
scale lift and corresponding banded precipitation will spread
northward into the lower Great Lakes. Models continue to be in
fairly good agreement showing the arrival of widespread
precipitation Thursday afternoon into Thursday night moving in
from the south. Thermal profiles will be critical during this
time period with profiles currently suggesting the column will
be cold enough for mostly snow, although boundary layer
temperatures will probably allow some rain to mix in at the
onset. The precipitation will diminish from west to east on
Friday as the low moves up the east coast into New England.


In the wake of the late-week coastal system...broad upper level
troughing will once again dominate our weather through the long
term period. This will ensure a continuation of well below normal
temperatures through early next week...with daily highs averaging
close to 10 degrees below normal. At the same time...such an
environment will also lead to continued opportunities for lake
effect precipitation downwind of the lakes.

Digging a little more into the forecast details...a general west
to west-northwesterly flow will be in place across our region
through Friday night and early Saturday...before perhaps turning
a little more west-southwesterly to southwesterly on Saturday in
advance of an approaching surface trough. Meanwhile...850 mb temps
should drop off to the -3C to -6C range Friday night...before
remaining in this general range or perhaps warming a little on
Saturday out ahead of the aforementioned trough. While certainly
cold enough for a lake response...such temps aloft will likely
not be cold enough to support all snow...with boundary layer
temperatures the main determining factor for precipitation type.
With this in mind would expect more of a mix of rain and snow
Friday evening and again on Saturday when boundary layer temps
will be warmer...with snow more predominant during the second
half of Friday night. Meanwhile...precipitation should be much
more widely scattered outside of the main lake effect areas...
with mainly dry weather prevailing the majority of the time. As
for temps...we can expect lows in the lower to mid 30s Friday
night...followed by highs in the mid 30s to lower 40s on Saturday.

The surface trough then looks to cross our region Saturday night
along with a more general chance of snow showers...with a west-
northwesterly flow of much colder but also drier air in its wake
then supporting scattered lake effect snow showers southeast of
the lakes later Saturday night through Sunday. With 850 mb temps
falling to around -13C...Sunday will easily be the coldest day of
the period...with highs struggling to get above the upper 20s and
lower 30s areawide - readings that are much more typical of mid
to late January than November.

Surface-based ridging and drier air should build into the region
Sunday night...and this in concert with warming/subsidence aloft
should result in lingering lake effect snow showers weakening to
the southeast and east of the lakes. By Monday the medium range
guidance diverges markedly with the GFS/GEM suggesting the passage
of another trough...while the ECMWF keeps the area mainly dry.
Given the distant time frame...for now have elected to lean more
optimistic and follow the latter scenario...with a mainly dry and
somewhat milder day forecast.


IFR CIGS continue through with some MVFR CIGS this afternoon as
a low moves northeast along the New England coast. Scattered
-SHRASN will slowly increase in coverage this afternoon.

This evening, cold air advection will begin to form bands of
lake effect snow to the southeast of both lakes. A concentrated
band will eventually develop between KROC and KSYR off Lake
Ontario. Off Lake Erie, some snow bands will continue variable
conditions between IFR and MVFR.


Wednesday...Mainly VFR, but IFR southeast of both lakes in lake
Thursday...Mainly VFR.
Thursday night and Friday...MVFR/IFR possible in rain and/or
wet snow.
Saturday...Mainly VFR, but IFR possible east of both lakes in
lake snows.


An area of low pressure off the mid Atlantic coastline this
morning will rapidly deepen today and tonight as it tracks
towards Atlantic Canada. A northwest wind developing around this
area of low pressure will increase today and tonight, bringing
both winds and waves to small craft advisory thresholds. High
pressure will then cross the lakes Wednesday and bring
diminishing winds and waves on the lakes, with SCAs ending.


NY...Winter Storm Watch from 7 PM EST this evening through
     Wednesday afternoon for NYZ004>006.
MARINE...Small Craft Advisory from 4 PM this afternoon to 4 PM EST
         Wednesday for LEZ040-041.
         Small Craft Advisory from 4 PM this afternoon to 4 AM
         EST Wednesday for LOZ030.
         Small Craft Advisory from 4 PM this afternoon to 10 PM EST
         Wednesday for LOZ043>045.
         Small Craft Advisory from 4 PM this afternoon to 4 PM EST
         Wednesday for LOZ042.



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