Area Forecast Discussion
Issued by NWS Buffalo, NY

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000
FXUS61 KBUF 052236
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
536 PM EST Thu Dec 5 2019

.SYNOPSIS...
A weak area of low pressure over Wisconsin will move across our
forecast area on Friday. This will produce a general snowfall
with most areas picking up a couple inches of accumulation. Some
nuisance lake snows in its wake will then be found southeast of both
lakes Friday night into Saturday. Milder weather can then be
anticipated Sunday into the start of the new work week.

&&

.NEAR TERM /THROUGH FRIDAY NIGHT/...
A lowering cap with the onset of weak warm advection this evening
will weaken and bring an end to the nuisance lake snows found
southeast of both lakes. There will be no rest for the weary
though...as a synoptic system is already on our far western
horizon.

A 100kt jet streak over the upper-most Mississippi valley this
evening will support an area of light snow that will gradually
blossom into a large area of accumulating snow as it passes through
the Lower Great Lakes on Friday. The expansion and intensification
of the approaching synoptic based snow will come as a result of an
associated sfc reflection becoming organized within a tight H925-
70 baroclinic zone under the aforementioned UL jet.

As the sfc wave approaches our region late tonight...it will evolve
into a weak `clipper-like` low that will cross our region during
the day Friday. Lift generated under the left front (exit region)
quadrant of the 100kt H25 jet will coincide with forcing from a 40-
45kt low level jet to produce a 4-6 hour burst of steady snow that
will cross our region LATE tonight through the first half of Friday
morning. Snow accumulations will generally total one to three
inches.

In the wake of the system...the widespread synoptic snow will give
way to more lake driven snows Friday afternoon and evening as H85
temps will drop off to around -10c. The deepening cold air will
prompt the limiting cap to rise to nearly 10kft...so this next round
of lake snow could include some moderately heavy activity times
Friday night. A general 300-310 steering flow will direct the lake
effect into the typical snowbelts southeast of both lakes where two to
four inches of accumulation will be possible. Outside of the main
lake effect areas...there could be enough scattered snow shower
activity to leave a coating in some areas. It will be a colder night
with mins in the teens away from the lake shores.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/...
Lake effect snow showers will continue into the morning on Saturday
southeast of Lake Ontario. Snow showers will further dissipate
through the morning as an area of high pressure tracks toward the
area. As ridging increases with the high approaching from the
southwest, lowering equilibrium heights and drier air will start to
reduce the lake response off of Lake Ontario. By the start of this
period, any lake response off of Lake Erie should be minimal to none
as the drier air and ridging from the approaching area of high
pressure gets to the Lake Erie area earlier.

Outside of any potential lake effect off of Lake Ontario, with the
area of high pressure centering over the Finger Lakes by mid-
afternoon on Saturday, the weather overall will be dry. This will
continue through the late day on Sunday as the area of high pressure
tracks east to the coast of New England by Sunday afternoon. As the
area of high pressure crosses the region, west to northwest winds
will shift to the south through the day on Saturday. As winds shift,
cold air advection will weaken and warm air advection will take over
from west to east. Before coming to an end, cold air advection will
cause the 850H temperatures to bottom out at around -12C across WNY
and to -15C east of Lake Ontario on Saturday morning. With the cold
air advection continuing through Saturday, high temperatures will be
in the low to mid 20s east of Lake Ontario and in the upper 20s to
near 30 for all other areas.

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

On Sunday, as the area of high pressure tracks farther east and a
trough approaches from the west, increased southerly flow will start
to increase warm air advection through the day. With the area of
high pressure influencing the weather, dry conditions are expected
across the area through the daytime hours. After early morning lows
in the upper teens to mid 20s, the afternoon highs will be in the
low to mid 30s east of Lake Ontario and in the upper 30s to mid 40s
across the rest of the area.

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.

On Monday, an area of low pressure centered over the mid-Mississippi
Valley will track northeast along the nearly stationary boundary to
Lake Huron by the evening on Monday, strengthening in the process.
This area of low pressure will strengthen in the left exit region of
a strengthening 250 jet with 250H winds reaching 160 kts as it
tracks northeast across the Great Lakes. Precipitation on Monday
will continue to overspread the region through the day, making for a
soggy first day of the workweek. Most of the precipitation on Monday
will be in the form of rain, but some snow or mixing with snow early
will be possible in the higher terrain. Highs on Monday will be in
the low to mid 40s across the higher terrain, and in the upper 40s
to near 50 in the lower elevations.

Monday night, the area of low pressure will track northeast from
near Lake Huron to western Quebec. As this system continues to track
northeast, its trailing cold front will approach the area. Forcing
and a continued moisture influx ahead of the front will help
continue the likelihood of rain across the area. Low temperatures
Monday night will be in the upper 30s to low 40s.

&&

.LONG TERM /TUESDAY THROUGH THURSDAY/...
Tuesday will be the big transition day. Temps will start out the day
in the 40s, then quickly drop to around freezing or below area wide
by the end of the day with rain showers changing over to snow
showers. Much colder air will follow for the remainder of the
period. Along with the cold air, the pattern appears favorable for
significant lake effect snow east of Lakes Erie and Ontario Tuesday
night through at least Wednesday night, possibly lingering into a
portion of Thursday.

Low pressure will deepen and consolidate as it moves into Quebec
Tuesday, with a trailing strong cold front moving across the eastern
Great Lakes region Tuesday. Showers will be likely Tuesday morning
ahead of the cold front, then transitioning over to snow showers
through the afternoon behind the front in the colder air, while
synoptically driven precipitation winds down. Still appears that it
will be a breezy to windy midweek as well, with the strongest winds
slated for Tuesday into Tuesday night, but still no worse than
advisory level at this time. This potential will continue to be
watched in future model runs given the favorable track of the low.

Following the cold front, the first shot of dramatically colder air
will move across the Great Lakes Tuesday afternoon. A reinforcing
shot of even colder air will pour across the Lower Lakes Wednesday
and Wednesday night, before slight modification of the airmass
begins later Thursday. The magnitude and depth of the cold air,
available moisture and position of upper level features all still
look FAVORABLE FOR A SIGNIFICANT LAKE EFFECT SNOW EVENT east of
Lakes Erie and Ontario. However, specifics are not possible in terms
of location and amounts at this time range. Stay tuned.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
Cigs of 2500 to 3500 ft late this afternoon should improve to
around 5000 ft by evening as the lake supported snow showers weaken
and become less widespread. The exceptions will be southeast of both
lakes where mainly MVFR cigs will accompany lake effect snow
showers. Vsbys in areas of lake snows will range from 2-5SM.

Mainly VFR conditions early tonight will then deteriorate...as weak
low pressure approaching from the Upper Great Lakes will lead to the
onset of widespread snow after 08z. Cigs will drop to MVFR levels
while vsbys will drop to IFR to LIFR levels across the far western
counties.

IFR to LIFR conditions in widespread snow can be expected thorugh
midday Friday. Slow improvement is anticipated for the afternoon and
evening.

Outlook...
Saturday and Sunday...VFR.
Monday...VFR to MVFR in rain showers.
Tuesday...MVFR in mixed precipitation.

&&

.MARINE...
Small craft advisories will progressively drop off tonight...as
fresh northwesterlies will gradually weaken with the passage of a
shortwave ridge.

In the wake of a clipper-like surface low on Friday...northwest
winds will freshen on both lakes Friday night. This could lead to a
new round of SCAs for Lake Erie and parts of Lake Ontario.

A large area of high pressure will pass over the Lower Great Lakes
on Saturday. This will support generally light winds and negligible
waves. Southerly winds will then freshen on both lakes late Saturday
night and Sunday. While this will push the highest wave action into
Canadian waters...rough conditions north of Mexico Bay could support
a SCA.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 8 PM EST this evening for LEZ040-
         041.
         Small Craft Advisory until 5 AM EST Friday for
         LOZ043>045.
         Small Craft Advisory until 10 PM EST this evening for
         LOZ042.

&&

$$

SYNOPSIS...RSH
NEAR TERM...RSH
SHORT TERM...SW
LONG TERM...Hitchcock/JM
AVIATION...RSH
MARINE...RSH


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