Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 250042

Area Forecast Discussion
National Weather Service Buffalo NY
742 PM EST Tue Jan 24 2017

A strong low pressure system will shift into the Gulf of Maine
tonight then move south of Nova Scotia Wednesday. Light snow will
taper off this evening as high pressure crosses the region tonight
and Wednesday. Another low pressure will then cross the region
Thursday ushering in a pattern change back to mid-winter conditions.
Heavy lake effect snows are possible east of lower Great Lakes
through the weekend.


The coastal low responsible for the widespread snowfall today
continues to spin off the New England coast, well south of
Nantucket. The trowal feature that aided in enhancing snowfall
across the Genesee valley this afternoon is starting to lift away
from the area and snowfall is diminishing in intensity across the
area at this time. Expect precipitation to continue to diminish over
the next several hours as the mid-level trough moves away to the
northeast, and mid-level moisture is stripped away. However,
lingering low-level moisture and upslope westerly flow will generate
areas of low clouds and fog across the Southern Tier and North-
Country overnight. BUFKIT profiles show little if any source of lift
aside from the orographic forcing, and suspect that this will not be
enough to produce any widespread drizzle/freezing drizzle concerns.

A ridge of high pressure will shift across the forecast area on
Wednesday with most of the day seeing dry weather with mostly cloudy
skies, thanks to moisture trapped underneath the ridge early in the
day, followed by increasing mid-level cloud cover as a warm front
lifts towards the region. Another area of low pressure will be
approaching from the Central Great Lakes late in the day with precip
likely holding off until Wednesday evening. Temperatures will warm
above normal as the flow becomes southerly ahead of the next system.
High temps will range from the low to mid 40s across Western NY to
the mid to upper 30s for Central New York.


Wednesday night and Thursday a potent closed mid level low will move
east through the Central Great Lakes and open up with time as it
gets absorbed by another trough moving through Quebec. At the
surface, low pressure will pass just north of Lake Erie and Lake
Ontario late Wednesday night and Thursday, with a trailing cold
front moving southeast across the area Thursday afternoon and
evening. Precipitation will come in several batches with this
system. A weak baroclinic wave will develop ahead of the trough
Wednesday night which is likely to produce rain showers crossing the
area from west to east.

The associated 500mb trough will cross the area on Thursday, with
associated DPVA resulting in another round of precipitation generally
light precipitation. This will be followed by more significant (but
localized) amounts Thursday afternoon and evening as winds shift to
the west behind the cold front and generate an upslope flow east of
the Lakes.

Precipitation type will be elevation dependent from Thursday morning
through early to mid afternoon, with mainly rain at lower elevations
and a rain/snow mix changing to all snow across higher terrain.
Temperatures will cool aloft with the passage of the disturbance
which will change precipitation to all snow late in the day. This has
the potential to produce several inches of snow across the Western
Southern Tier extending in to the Boston hills.  A bit more snow is
likely on the Tug hill, possibly approaching advisory amounts. After
this, slightly drier air should briefly build behind the front which
will diminish snowfall rates late Thursday night. Accumulation
across lower terrain should be minimal, mainly less than an inch.

By Friday, temperatures aloft will be cold enough to support lake
effect snow with 850mb temps around -10C through Friday night. The
key to our forecast will be the progression of a shortwave which
model consensus brings across the area late Friday. Westerly winds
will briefly shift to the southwest in advance of this shortwave,
then return to the west behind it. The shortwave will also enhance
moisture which will result in a period of moderate to heavy snow
east of the lakes. There is still uncertainly in the timing and
location of lake effect bands because of subtle differences in the
progression of the shortwave and differences in forecast wind
fields. In general, the greatest amounts should be focused across
the traditional snow belts east of the lakes, however the band may
meander north toward the Buffalo metro area late Friday in advance
of the shortwave. There is not yet enough forecast confidence to
issue a watch, however it is possible snowfall amounts may
approach warning criteria in some locations on Friday and Friday
night. Either way, this appears to be the start of a much more
winter-like pattern than it has been for the past couple weeks.


For the Saturday through Monday time period our region will remain
active, with several shortwave troughs refreshing a cold airmass
over the airmass that will become cold enough to support
lake effect snow. The shortwaves will alter the low level wind field
through the period, allowing the lake effect bands to
oscillate...but a general northwest flow will make the Southern
Tier/Ski Country as well as SE and E of Lake Ontario prime real
estate for accumulating lake snows...that could become significant.

Temperatures at 850 hPa will average -10 to -13C below zero Saturday
through Sunday supporting lake effect snow off lakes that are around
+2C (Erie) and +5-6C (Ontario). Lake induced equilibrium levels will
rise to around 10K feet and with the shortwaves bringing increased
synoptic moisture lake effect snow bands will become strong.

A comparison of the surface and upper level patterns to our locally
developed lake effect analogs show a good match to significant
events for the Chautauqua Ridge and Tug Hill/Oswego County. CIPS
analogs continue to also support the idea of a significant event. By
Sunday night it is quite possible that several feet of snow will
accumulate across the Chautauqua ridge, and east of Lake Ontario.

On Monday temperatures will drop to around -15 to -19C over the
region, bringing what will be the chilliest day this period. An
upper level ridge will near the region Monday night, and this
feature will likely end the lake effect snow through Monday night.

By Tuesday behind the ridge axis, much warmer air aloft will briefly
squeeze northward...ending any lingering snow east of Lake Ontario
early in the day, and likely providing a brief period of dry
weather. Another shortwave will near the region late in the day
Tuesday, or Tuesday night. This feature will bring additional light
snow to the region before ushering another round of arctic air to
begin the month of February.

Air temperatures just above normal Friday, will fall to near normal
Saturday-Sunday and then below normal Monday. On Tuesday ahead of
the shortwave many areas will likely rise just above freezing.


IFR conditions continue to be found across the Genesee valley this
evening as a snow band associated with a mid-level trough continues
to impact the area. This snow should taper off over the next couple
of hours as the trough weakens and pulls away to the
northeast.However, lingering low level moisture and upslope westerly
flow will keep IFR conditions in place across many areas through
the rest of tonight into early Wed morning, with only a gradual
improvement to MVFR cigs expected on Wednesday morning. Elsewhere,
expect MVFR cigs to generally prevail elsewhere through the balance
of the period, with cigs gradually increasing through the day
Wednesday as a warm front approaches the region.

Wednesday night and Thursday...VFR/MVFR with a chance of
rain and snow. Friday to Sunday...VFR/MVFR with IFR in lake effect
snow showers.


Ridging will build in across the area briefly tonight and Wednesday,
which will provide light winds and wave action. We will return to
more typical mid-winter conditions by this weekend with lake effect
snows and likely much choppier conditions on both lakes.





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