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Area forecast discussion
National Weather Service Buffalo New York
437 am EST Fri Dec 6 2019

Synopsis...
a small area of low pressure will cross the area today and produce
an area of snow with a few inches of accumulation, mainly north of
the thruway. Warmer temperatures may allow for some rain to mix in
briefly across western New York and the western Finger Lakes, keeping any
snow accumulations to a minimum. Following this system, lake effect
snow showers will develop southeast of the lakes late this afternoon
through tonight with some additional accumulation, especially
southeast of Lake Ontario. High pressure will then bring a return to
dry weather Saturday.

&&

Near term /through tonight/...
warm advection and moisture transport ahead of the next system will
allow some flurries and light snow to overspread the area through
daybreak.

A small, compact clipper low will move across the eastern Great
Lakes this morning and midday, supported by a mid level shortwave
and 100+ knot upper level jet streak. Model guidance has trended a
little north with the track of this clipper since yesterday, only
about 30 miles or so, but that will make a difference in sensible
weather given how small the feature is. Large scale forcing in the
DPVA regime ahead of the trough will support isentropic upglide
ahead of the surface low, with a ribbon of frontogenesis in the 900-
700mb layer just north of the low track providing the strongest
focus for widespread precipitation. Given the slightly farther north
track, the most widespread snow will be found over and east of Lake
Ontario, and also clipping the first row of counties south of the
Lake Ontario shore.

NAM based guidance, including the higher resolution mesoscale
windows and thus href are generally higher in qpf, and seem too
aggressive and slightly too far south with the highest snowfall axis
given the weaker, farther north solutions of the GFS/Gem. Given
this, and the marginal surface temperatures, kept accumulations
around 2 inches from Orleans to Wayne counties, and 2-4 inches
across Oswego and southern Lewis counties where forcing and
residence time appear to maximize. The relatively mild surface
temperatures will limit the impact this can have on paved surfaces,
especially given the snow will be falling during peak insolation on
roadways.

Along and south of the New York thruway, including the Buffalo area,
precipitation will be more intermittent, primarily focused on the
warm advection early this morning, and then along the cold front
during the late morning and early afternoon. It will also become
warm enough to allow some rain to mix in briefly from Buffalo
southward through the western southern tier and into the western
Finger Lakes and Genesee Valley. This will keep accumulations to a
minimum, with less than an inch expected primarily early this
morning before temperatures rise above freezing.

Precipitation with the clipper system will rapidly exit from west to
east during the early to mid afternoon. Cold advection will increase
behind the system, and set the stage for some limited northwest flow
lake effect snow. Off Lake Erie, the lake snow will peak in coverage
during the early evening as equilibrium levels briefly rise to
around 10k feet. Northwest flow will focus most of the snow showers
into the Chautauqua ridge, with an inch or so of accumulation in
persistent bands. This will be short lived, with snow showers ending
overnight as high pressure and associated lowering inversion heights
build over Lake Erie.

Lake Ontario will have a little more time to work with, as favorable
conditions last through early Saturday morning. Lake induced
equilibrium levels briefly rise to around 10k feet this evening, and
stay above 8k feet through 12z Saturday. Latest mesoscale guidance
suggests a Georgian Bay connection will develop for several hours
later tonight, yielding the best band organization southeast of Lake
Ontario from roughly midnight through 6am Saturday. West-northwest flow
direction will favor northern/eastern Wayne, northern Cayuga, and
southern Oswego counties. This may produce another 2-4 inches of
accumulation tonight. Slightly higher advisory level amounts cannot
be ruled out if the banding becomes nearly stationary for long
enough, but confidence is not high enough to raise the advisory at
this time.

Outside of these two Main Lake effect areas, a few flurries and
scattered snow showers will likely occur later this afternoon
through the first half of tonight courtesy of Lake Huron, but any
accumulations will be localized and minor.

&&

Short term /Saturday through Sunday night/...
cold northwest flow continues into Saturday. This will maintain lake
effect snow showers primarily focused southeast of Lake Ontario.
Inversion heights will only be around 4-5kft, with some semblance of
shallow moisture, so additional snowfall should be limited to no
more than an inch or so. Upstream high pressure and drier air will
start to arrive during the day which will shallow out the moisture
further with the low level flow turning more anticyclonic.
Therefore, would expect any Overlake convection to weaken/wane by
afternoon. Outside of the Lake Ontario lake effect snow the
remainder of the area will be dry. High temperatures will be in the
lower to mid 20s east of Lake Ontario and in the upper 20s to near
30 for all other areas.

Dry and chilly conditions will continue through Saturday night as
the area of high pressure slides east through the night.
Temperatures will be in the teens east of Lake Ontario, and in the
upper teens to mid 20s for the higher terrain to the lake plains.

The area of high pressure tracks to the east Sunday as a trough
approaches from the west. Increasing southerly flow between the two
systems will send a surge of warmer air into the region. After a
cold start to the day, temperatures will rebound into the upper 30s
to mid 40s across the region. High pressure off to our southeast
will continue to influence our weather Sunday keeping the day dry
with showers associated with the approaching trough holding off
until Sunday night. Tightening graident across the area will bring
increasing winds with most areas seeing gusts of 25 to 35 mph with
favored downslope areas possibly exceeding 40 mph at times.

Sunday night, a frontal boundary and trough will slowly track toward
the area. As the boundary tracks east, weak waves of low pressure
will track northeast, increasing our chances for precipitation.
Chance pops will cover far wny by the late evening, and continue to
increase from west to east through the night. Increased forcing and
increasing moisture will cause precipitation to track farther east
into the area, and most locations will have likely pops by daybreak
on Monday. As precipitation starts, it should be mostly in the form
of rain, but some higher spots where the temperatures remain cooler
could see some mixing with or change to snow. Lows Sunday night will
be in the low to mid 30s across the higher terrain, and in the upper
30s to near 40 for the lower elevations.

&&

Long term /Monday through Thursday/...
..significant lake effect snow event continues to look favorable by
middle week...

Next trough will push from the northern plains into the Midwest
Monday. The initial low over Ontario will lay out a front that will
start to push south toward New York state during the day Monday.
Meanwhile, a strong southern stream jet working through the Central
Plains will result in the development of a low that will then
strengthen while lifting northeast along the front through lower
Michigan into southern Ontario by Monday evening. Warmth of the
resident airmass and track of the low northwest of the area will
result in a rain event across western and north central New York
Monday and Monday night. Temperatures on Monday will be mild for
December standards with most highs in the upper 40s to lower 50s,
with lower to mid 40s across the higher terrain.

An Arctic front will pass quickly through the area Tuesday allowing
cold air to surge into the region. Ongoing rain showers Tuesday
morning will transition over to snow showers through the afternoon
as the cold air deepens.

Arctic air will continue to pour into the region Tuesday night
through Wednesday night with 850 mb temperatures dropping to near
minus 20c. This will allow for a Strong Lake response off both Lake
Erie and Lake Ontario during this time period. As is the usually the
case this far in advance, there remains some uncertainty with
respect to exact location of the lake snows, but current lower
resolution models suggesting a general west or west-southwest flow
will dominate for much of the time period before veering northwest
near the end of the event.

It continues to look like all parameters are in place from extreme
over-lake instability, available moisture and position of upper
level features for significant lake snows downwind of both Lake Erie
and Lake Ontario during the Tuesday night through at least the
Wednesday night time frame.

&&

Aviation /10z Friday through Tuesday/...
a small clipper system will move through the area today. This will
support an area of snow along and north of its track, with the
steadiest snow falling over Lake Ontario and areas just south of the
lake, as well as the Eastern Lake Ontario region. Expect a 4-6 hour
period of IFR visibility and MVFR ceilings within this area of snow this
morning through early afternoon. Along and south of the low track,
the snow will be more intermittent and nature, and may even mix with
some rain at kbuf, kiag, and kjhw briefly during the late morning
and midday as surface temperatures warm above freezing. Expect
mainly MVFR visibility/ceilings in this area, with a brief period of IFR in
snow showers as a cold front crosses during the late morning and
early afternoon.

The widespread snow for northern areas will taper off this afternoon
as the small system moves east of the area. This will be replaced by
northwest flow lake effect snow showers southeast of the lakes. This
will produce areas of IFR visibility southeast of Lake Erie this evening,
including kjhw at times. This will taper off overnight as high
pressure builds over Lake Erie. Areas of IFR visibility will also develop
southeast of Lake Ontario tonight in lake effect snow showers,
mainly from just east of kroc to near kfzy. Ceilings will generally be
MVFR late this afternoon through tonight, with some local IFR
possible for higher terrain and in a few of the more organized bands
of lake effect snow showers.

Outlook...
Saturday...local MVFR/IFR in lake effect snow showers southeast of
Lake Ontario early, otherwise VFR.
Sunday...VFR.
Monday...areas of MVFR in rain showers.
Tuesday...MVFR with rain showers ending from west to east. Snow
showers possible late.

&&

Marine...
a small clipper low will move across the eastern Great Lakes this
morning through midday. A brief period of moderate southwest winds
will develop on Lake Erie today as the low moves just north of the
lake, producing Small Craft Advisory conditions, which will linger
into this Evening. Lake Ontario will initially not be impacted by
these winds today, but west-northwest winds will increase tonight in the wake
of the clipper. This will produce a brief period of Small Craft
Advisory conditions tonight through Saturday. Winds and waves will
diminish later Saturday as high pressure builds into the eastern
Great Lakes.

&&

Buf watches/warnings/advisories...
New York...none.
Marine...Small Craft Advisory until 1 am EST Saturday for lez040-041.
Small Craft Advisory from 11 PM this evening to 4 PM
EST Saturday for loz043-044.
Small Craft Advisory from 9 PM this evening to 10 am EST
Saturday for loz042.

&&

$$

Synopsis...Hitchcock
near term...Hitchcock

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