Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 230250
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
950 PM EST Mon Jan 22 2018

.SYNOPSIS...
A sprawling storm system over the Upper Mid West will push a strong
frontal across the region tonight and early Tuesday...and this will
generate a round of soaking rain. Falling temperatures in the wake
of the front on Tuesday will not only allow leftover rain to change
to snow showers...but will promote some lake snows in the snowbelts
east of both lakes. Seasonable temperatures during the middle of the
week will then once again give way to warmer conditions by the
weekend.

&&

.NEAR TERM /THROUGH TUESDAY/...
A large storm system centered over the mid western states has pushed
a pair of warm fronts northward across our forecast area. The first
of these surface boundaries is hung up over Lake Ontario and
demarcates wintry conditions to the north and continued warming to
the south. More on this in a moment. The second `warm front`
stretched from just north of Buffalo at 03z to the Finger Lakes
region. This boundary is marked by notably higher cigs to its south
and a spike in temperatures into the 50s in the Buffalo metro area.
Meanwhile a third front in the form of a strong surface occlusion
was approaching our region from Ohio. As for the weather associated
with these features...

A winter weather advisory remains in place for Jefferson County and
the Thousand Islands region where freezing rain was still being
reported as of 00z. As is so often the case...a stubborn northeast
wind in the St Lawrence Valley is feeding low level cold air into
the overrunning milder air above 1500 feet. This scenario should
persist through this evening...allowing up to a third of an inch of
ice to accumulate from Watertown northward.

As we push through the overnight...a band of rain will cross the
western counties. This band has become less organized since 00z...
but is found just ahead of the aforementioned surface occlusion and
will be forced by moderately strong low level convergence ahead of
the boundary and strong lift provided by a coupled upper level jet.
The increasingly broken band of rain should last for about 3 hours
across the western counties while dropping a quarter to a half inch
of rain. As the boundary pushes across the Eastern Lake Ontario late
tonight and early Tuesday...a wave along the front will slow its
eastward progression so the rain will last a couple hours longer for
that region. A reminder that a flood watch remains in effect for all
of western New York until Tuesday evening.

Behind the cold front precipitation will come to an end for a brief
period as the dry slot works through the forecast area Tuesday
morning. Additionally, colder air will begin to work its way into
the region. Although, this time around it will not be a quick
transition over the snow with the cold front. 850H temperatures will
gradually drop to -5C by late Tuesday evening with the arrival of
mid-level trough.  As the mid level trough arrives strong PVA will
introduce another round of showers which will change to snow as
deeper and colder air arrives late in the day.

The combination of snow melt and a half to three-quarters of an inch
of rain fall will introduce the potential for ice jams. A flood
watch remains in effect from this afternoon through Tuesday with
additional details in the hydrology section below.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH FRIDAY NIGHT/...
Precipitation will still be ongoing Tuesday night across western and
north central New York, but diminishing in coverage over time as the
synoptic system gradually pulls away. Colder air advecting in behind
the departing system will transition any lingering rain or mixed
precipitation to all snow by midnight, but this will occur earlier
across upslope areas east of the lakes. There is a small chance of
some patchy freezing drizzle late Tuesday night as forecast
soundings show saturated low levels just barely extending up to
around -10C. Otherwise remaining synoptic snow will give way to some
lake enhanced/upslope snow showers southeast of the lakes overnight
as 850 mb temperatures drop to around -10C. Higher elevations
southeast of the lakes could see a 2-3 inch accumulation Tuesday
night.

850 mb temperatures continue to cool settling to around -14C during
the day Wednesday, which will be a bit better for lake effect snows
showers to linger southeast of the lakes, but moisture profiles are
very shallow. Could see an additional 1-2 inches for inland areas
where terrain adds a boost to lift, but that should be about it.

Light lake effect snows may linger into Wednesday night before
winding down on Thursday, as surface ridging moves across the lower
Great Lakes. This should lead to a return of sunshine on Thursday,
though northwesterly flow aloft will keep it cold across the region,
with highs ranging from the lower teens in the North Country to the
lower to mid 20s in western New York. Wednesday night will likely be
the coldest night of the week, with lows in the lower teens across
most areas, except for the North Country, which will be flirting
with sub-zero temperatures.

Warm air advection regime will get underway Thursday night, then
strengthen Friday and Friday night in response to a trough moving
into the western CONUS. During the warm air advection, isentropic
ascent is not very impressive and this combined with drier air in
the lower to mid levels, do not expect any precipitation during this
time period.

&&

.LONG TERM /SATURDAY THROUGH MONDAY/...
An upper level trough will move across the Great Lakes Saturday
while associated low pressure will move across James Bay and into
Quebec. A cold front will likely be stretched across the Mid-West
Saturday while a 50kt southerly LLJ transports moisture from the
Gulf of Mexico and into the Great Lakes. The jet will interact with
the upper level trough and rain showers are likely Saturday into
Sunday. There is spread in rainfall amounts Saturday-Sunday with the
12z ECMWF being on the wet side. At this time, hydro concerns are
not anticipated due to the low confidence however will need to watch
for potential issues on rivers.

Temperatures will likely reach the 40s Saturday and Sunday and the
mid 30s Saturday night. The cold front will cross the eastern Great
Lakes Sunday/Sunday night. Temperatures will drop into the 20s
Sunday night. Colder temperatures behind the front may lead to a
lake response into Monday.

&&

.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
A fairly strong frontal boundary will push across the western
counties overnight...and will finally make its way across the
Eastern Lake Ontario region early Tuesday morning. This will result
in cigs of 2500-3500 feet...with MVFR vsbys during the heaviest
pcpn. The exceptions will be along the south shore of Lake Ontario
and also at KART and KGTB through 04z...where an east to northeast
flow will keep IFR/LIFR cigs in place. These very low cigs will be
accompanied by -FZRA from KART north to the Thousand Islands.

On Tuesday...the steady rain will give way to more showery pcpn with
mainly VFR conditons anticipated. As we push through Tuesday
afternoon and evening though...the pcpn will change to snow with
MVFR conditions coming back into play.

Along with the pcpn tonight...winds just off the surface will be
from the south at 40 to 50 knots. This will keep low level wind
shear in place through daybreak for all sites.

Outlook...

Tuesday night...MVFR/IFR within lake effect snow east and southeast
of both lakes.
Wednesday...VFR/MVFR with a chance of snow showers.
Thursday and Friday...VFR.
Saturday...Mainly VFR with a chance of showers.

&&

.MARINE...
Low pressure over the Upper Midwest will track across the Central
great Lakes sending its associated cold front towards the region.
Southwesterly winds and waves will pick up just ahead and behind the
cold front reaching Small Craft Advisory Levels on Lake Erie
tonight. A Small Craft Advisory had been issued for Lake Erie from
03Z Tuesday to 06Z Wednesday. Winds will become Westerly Tuesday
night reaching Small Craft levels on the eastern end of Lake Ontario
from 23Z to 18Z Wednesday.

&&

.HYDROLOGY...
A flood watch for ice jam flooding is in effect for all of
western New York into Tuesday evening.

Temperatures continue to hover in the low to mid 40s across
much of western New York allowing a continuation of the
snowpack across the region to melt. Temperatures will remain
above freezing into Tuesday evening...with daytime readings
peaking between 45 and 50 and widespread rain coming tonight.
This will allow a true melt down of the snowpack over the
western counties with the runoff flowing into creeks...many of
which are ice covered/clogged.

Using research proven over several decades...the melting degrees
experienced from the above described temperature forecast
suggests that ice jam flooding could prove to be a problem as
early as this afternoon. This potential problem will be
exacerbated by a general quarter to as much as three quarters
inch of rain later today through tonight.

While there will be a risk for ice jam flooding...a less
impressive snowpack...lower temperatures and less rainfall
compared to last weeks flooding should translate into more
localized flooding. In other words...flooding should not be as
widespread as the last event. In any case...those living in
areas prone to ice jam flooding should pay attention to water
levels and subsequent statements and warnings issued by the
Buffalo National Weather Service office.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Winter Weather Advisory until 1 AM EST Tuesday for NYZ007.
     Flood Watch through Tuesday evening for NYZ001>005-010>014-
     019>021-085.
MARINE...Small Craft Advisory until 1 AM EST Wednesday for LEZ040-041.
         Small Craft Advisory until 2 PM EST Wednesday for
         LOZ042-043.
         Small Craft Advisory from 6 PM Tuesday to 1 PM EST
         Wednesday for LOZ044-045.

&&

$$

SYNOPSIS...RSH
NEAR TERM...AR/RSH
SHORT TERM...TMA
LONG TERM...HSK
AVIATION...RSH
MARINE...AR
HYDROLOGY...RSH/SMITH


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