Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 222119
AFDBUF

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

.SYNOPSIS...
Lower pressure will move across the Upper Great lakes sending its
cold front across the area with another round of rain tonight.
Behind the cold front it will turn much colder with lake effect snow
showers expected east of the lakes through Wednesday. High pressure
builds into the region Thursday with a warming trend into the
weekend.

&&

.NEAR TERM /THROUGH TUESDAY/...
Surface analysis depicts the warm front near the south shore of lake
Ontario across far northern Western NY and stretching to the east
into Central NY. A widespread surge of isentropic lift, which is
currently producing an area of light rain from Monroe/Ontario
counties northeast into North Central NY (Oswego/Lewis counties)and
is lifting to the NE late this afternoon. East and northeast of lake
Ontario in the Saint Lawrence Valley NE flow has allowed a layer of
shallow sub freezing temperatures to persist creating a wintry mix
of snow/sleet/freezing rain with temperatures in the 20s as of 19Z.
Temperatures will struggle to climb above freeze as the shallow
layer will remain entrenched for a good portion of the evening hours
and tonight. A Winter Weather Advisory remains in effect for
Northern Jefferson County to cover the Saint Lawrence Valley through
1 AM Tuesday for this wintry mix.

Low pressure over the Upper Midwest will move into the Central Great
Lakes tonight and into New England by Tuesday evening. As it does
so, its associated cold front will push east towards the lower Great
lakes. Ahead of the cold front southerly winds will pick up aided by
50 plus knot LLJ. Convergence along the front combined with the LLJ
with produce another round of precipitation tonight as the cold front
moves across the region. 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 /21Z MONDAY THROUGH SATURDAY/...
A warm front is lifting NE of Western NY with the back edge of the
widespread light rain showers slowly exiting the Niagara Frontier
and Genesee Valley early this afternoon. LIFR/IFR conditions persist
at IAG/KROC/JHW but conditions will gradually improve at these
terminals through the rest of the afternoon hours behind the warm
front. Further east, KART will see deteriorate conditions as
precipitation overspreads North Central NY. Expect MVFR conditions
with a period of -FZRA between 17Z-00Z across Jefferson county and
the Saint Lawrence Valley where persistent NE flow will lock in a
shallow layer of sub freezing air.

Tonight, low pressure will track NE into and across the Great Lakes
region sending its cold front towards the Lower Lakes with another
round of widespread rain. As the precipitation overspreads Western
NY conditions will deteriorate with MVFR CIGS/VSBYS and low level
wind shear as a strong LLJ pushes into the region. Tuesday, expect
continued MVFR conditions as a strong mid-level short wave trough
brings in a much colder air mass with more showers changing to snow
showers.

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 from 10 PM this evening to 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...AR
NEAR TERM...AR
SHORT TERM...TMA
LONG TERM...HSK
AVIATION...AR
MARINE...AR
HYDROLOGY...RSH/SMITH


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