Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 220551

Area Forecast Discussion
National Weather Service Buffalo NY
151 AM EDT Wed Mar 22 2017

Behind an arctic front, cold air will flow over the eastern Great
Lakes region today, producing air temperatures that are more like
that of January. Scattered lake effect snow southeast of Lake
Ontario this morning will end as dry air pushes across the lakes.
Air temperatures will then rebound markedly tomorrow and Friday as
much warmer air works its way back into our region...with an
extended period of wet weather set to begin Friday and last right
through early next week.


Behind an arctic front, cold air will quickly deepen overnight,
with the airmass briefly becoming supportive of lake effect
snow showers as the lake induced equilibrium levels rise to
around 9K feet. While instability will be decent, the very dry
nature of the synoptic scale airmass and short northwest fetch
will greatly limit intensity. Expect a broad spray of light snow
showers across most of the area overnight, with the best
coverage expected across the Chautauqua Ridge just inland from
Lake Erie with an added boost from upslope flow, and also
southeast of Lake Ontario from Wayne to Oswego counties.

Regarding snow accumulations, expect these will be very light, on
the order of a coating to an inch in the most persistent lake
streamers overnight. The main reason for such limited amounts will
be the very dry nature of the arctic airmass, combined with a the
shorter/non-ideal northwest to southeast fetch across the lower
Great Lakes. Temperatures by Wednesday morning will bottom out in
the teens, with even some single digits in the north country. It
will be a rude awakening for most as you head out the door Wednesday
morning when factoring in the wind chill, it will feel like 0 to 5
below in most areas, and 10 to 15 below across the North Country.

Temperatures will recover little through the day on Wednesday, as
arctic high pressure builds in across the region. Lingering lake
effect snow showers will fizzle out as the capping inversion lowers,
along with diurnal effects and a very dry airmass. There will be
increasing amounts of sunshine by the afternoon, however with 850 mb
temps -teens to -20C, highs will only be in the 20s for most
locations, and even teens across the North Country.


Western and North-Central New York will enjoy a period of fair and
tranquil weather from Wednesday evening through Thursday afternoon,
as an expansive arctic high passes over the region. Clear skies and
light winds Wednesday night will promote widespread radiational
cooling, and given the residual cold and dry air in place across the
region, temperatures will plunge into the single digits across the
Southern Tier and potentially below zero in the North Country, with
low teens along the lake plains. These will likely be the coldest
readings we will encounter until next winter, as temperatures will
rebound into spring by the end of the week. Temperatures on Thursday
will remain slightly below average, as the last vestiges of Arctic
air make their way east as the center of the high moves to the
Eastern Seaboard.

Increasing return flow will advect increasingly warm and moist air
northwards into the Great Lakes starting Thursday night. This will
lead to increasing clouds and a much milder night Thursday night,
relatively speaking, with lows ranging from the lower 20s in the
North Country to just below freezing across far western New York.
With this increasing warm advection, we will start to see
precipitation develop across the forecast area Thursday night into
early Friday morning from west to east, as isentropic uplift and
DPVA aloft increases across the area. With temperatures still below
freezing, there will be a risk for snow and/or mixed precipitation
before temperatures warm above freezing later in the night and
precipitation changes over to rain.

By the time we move into Friday, warm advection will be in full
force across the region, with increasing baroclinicity and
frontogenesis across the Great Lakes and upper Midwest as warm air
surges northwards across the region while anticyclonic flow around
high pressure over northern Manitoba brings cold and dry air south
towards the Great Lakes. This, in addition to deformation along the
emerging boundary, will lead to the development of widespread,
persistent, and occasionally heavy rainfall across the region and
the forecast area starting Friday and lasting through much of the
weekend. While precipitation will be all rain during the day on
Friday, as temperatures should range from near 50 in Western NY to
around 40 in the North Country, given the aforementioned baroclinic
gradient that will be in place across the region, temperatures in
the North Country, and in the Saint Lawrence valley in particular,
will be close enough to freezing Friday night to maintain a concern
for a changeover back to mixed precipitation overnight.


Consistent run to run agreement among the global medals continues a
high confidence expectation for a long-lasting wet period running
through this weekend into at least the middle of next week. The
major players in this set up will be back-to-back cut-off mid/upper
level lows that will provide and extended period of synoptic lift
and moist southerly flow across the Ohio Valley and eastern Great
Lakes that will interact with a quasi-stationary east-west frontal
boundary extending across Lower Michigan, New York and southern New
England. While the boundary will likely undulate north and south
several times during this extended period, the exact placement of
the boundary at any specific time will be key to both temperatures
and p-type. Areas to the south will mainly feature warmer temps
(upper 40s into the 50s) with plain rain while areas north of the
boundary will see cooler temperatures under a northerly flow (30s
and lower 40s with some 20s possible in the North Country) with a
threat for a mixed wintry precip including some ice. A rough mean
placement at this range seems to be running east-west somewhere
between the NY Thruway corridor and Lake Ontario.

As mentioned above, there will be back-to-back cut-off lows to
content with. The first will provide the forcing for wet weather
Saturday and Sunday while shifting from the Central Plains northeast
across the Great Lakes followed on its heals by the second cut-off
low following a similar track Monday and Tuesday. In terms of QPF, a
rough average accumulated total among the models through Tuesday is
1.5 to 2.5 inches across the frontal boundary running across western
and central NY. While the long duration of this event should not
bring any flash flooding concerns, river and stream rises and areal
flooding of low-lying areas may be possible. If sub-freezing air
remains locked at the surface on the north side of the front there
could also be a threat of some significant ice accumulations but the
lowest confidence is found in that scenario. Overall, confidence on
the specific placement of any weather hazards during this period is
fairly low at this range which has precluded a mention in the
Hazardous Weather Outlook.


A secondary arctic front continues to push southward across the
region, with a few burst of snow along the boundary. This snow will
near KART and KROC, and KJHW with perhaps a brief period of MVFR
flight conditions. A little IFR may develop this early morning SE of
Lake Ontario as added lake moisture brings increased amounts of

Much drier air will flow in from the northwest today, ending
scattered snow showers and allowing for VFR flight conditions to
prevail. It will become a little breezy this afternoon, with winds
reaching into the 20 knots range.

Tonight sprawling area of high pressure will reach the region with
lighter winds and VFR flight conditions continuing.


Friday...Deterioration to MVFR/IFR with mixed rain and snow
developing...then changing over to all rain.
Saturday and Sunday...MVFR/IFR with rain likely.


After a few days of relatively tranquil conditions...strong
northwesterlies will overspread the entire Lower Lakes region
following the passage of the front tonight...then continuing through
a good chunk of Wednesday. To cover the resultant increase in winds
and wave action...Small Craft Advisories have been hoisted as
outlined below.

After that...strong high pressure will build across the region
later Wednesday through Thursday while bringing a return to
light winds and negligible waves.


MARINE...Small Craft Advisory until 2 PM EDT this afternoon for LEZ040-
         Small Craft Advisory until 2 PM EDT this afternoon
         for LOZ030.
         Small Craft Advisory until 2 AM EDT Thursday for LOZ043-
         Small Craft Advisory until 5 PM EDT this afternoon for



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