Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 212044

Area Forecast Discussion
National Weather Service Buffalo NY
444 PM EDT Tue Mar 21 2017

An arctic frontal boundary, accompanied by scattered snow showers,
will move across the region tonight and usher in much colder
temperatures and some lingering lake effect snow showers through
Wednesday morning. Temperatures will then rebound markedly Thursday
and Friday as much warmer air works its way back into our
region...with wetter conditions also arriving in time for Friday and


Quiescent conditions will continue across most of Western and
Central NY through this evening with mainly clear skies. The one
exception is east of Lake Ontario where low stratus remains across
the higher terrain. A pre-frontal trough will move across the Saint
Lawrence Valley through early evening, and produce a few scattered
showers mainly north of Jefferson County.

Otherwise our attention turns to the main arctic cold front
boundary, which can easily be picked out in surface observations,
satellite imagery across northern Michigan and Ontario province. In
the wake of the frontal passage, temperatures are dropping from the
30s/40s to the teens/20s across upper Michigan and Ontario.
Convective snow showers associated with steep lapse rates under the
upper-level low are also being enhanced by lake induced instability
over the upper-Great Lakes with numerous streamers developing off
Lake Superior. This trend will continue into western and north
central NY later this evening as the boundary crosses the region.
Have maintained scattered snow shower wording in the forecast as
upstream data supports a broken line of snow showers moving through
with the front, then scattered lake effect snow showers lingering
southeast of Lakes Erie and Ontario behind the front overnight.
Highest PoPs are positioned southeast of the Lakes where added lake
moisture and instability will make snow showers and light
accumulations more likely. Regarding snow accumulations, expect
these will be very light, on the order of a coating to an inch or
two 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 near 0F across western NY and 5 to
10 BELOW zero in 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
some breaks to more sunshine by the afternoon, however with 850 mb
temps -teens to -20, highs will only be in the 20s for most


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.


Low stratus across the higher terrain east of Lake Ontario will
continue to produce areas of MVFR CIGS through early evening.
Otherwise the rest of the area will remain VFR with mainly clear
skies. An area of low stratus and fog over central Lake Erie will
likely remain away from the TAF sites and be cleaned out by the
approaching arctic front early this evening.

An arctic front will then cross the region tonight and bring some
additional scattered snow and rain showers to the Finger Lakes and
North Country...with a north-northwesterly flow of much colder air
in its wake helping to generate some scattered light snow showers
and flurries southeast of the lakes. Expect the potential for brief
reductions to MVFR/IFR within any snow showers... with general high-
end MVFR to lower-end VFR conditions otherwise prevailing.
Conditions will improve back to VFR Wednesday as cold, but very dry
air builds into the area.


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 from 8 PM this evening to 2 PM EDT
         Wednesday for LEZ040-041.
         Small Craft Advisory until 2 PM EDT Wednesday for
         Small Craft Advisory until 2 AM EDT Thursday for LOZ043-
         Small Craft Advisory until 5 PM EDT Wednesday for LOZ042.
         Small Craft Advisory from 8 PM this evening to 5 PM EDT
         Wednesday for LOZ045.



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