Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 212200

Area Forecast Discussion
National Weather Service Buffalo NY
500 PM EST Sun Jan 21 2018

A warm front will push north from the Ohio Valley tonight and then
move across the area Monday. Some light rain is possible tonight,
but more significant rainfall is expected Monday and Monday night,
as a large storm system tracks through the Great Lakes, with
temperatures warming well into the 40s ahead of this system. A cold
front will then bring back more typical winter weather late Tuesday
into Thursday. Another warm up is forecast Friday into next weekend.


Low pressure continues to develop to the lee of the Rockies over the
Central Plains, with its associated warm front extending eastward
from the developing low through the Central plains into the Ohio
Valley. Increasing moisture continues to gradually advect northward
along and north of this boundary into the Ohio Valley and southern
Great Lakes. Closer to home, this has resulted in thickening and
lowering of clouds and some patchy fog, but very little in the way
of precipitation.

As we head into tonight, low level moisture will continue to advect
into the region from south to north ahead of the warm front. There
still could be some intermittent very light precipitation this
evening, but it continues to appear that the better chances for
precipitation will hold off until late tonight into Monday morning,
increasing from south to north, as moist isentropic ascent increases
along and north of the warm front.

A several hour period of warm frontal precipitation will push
through the region during the day Monday. For most areas, this
precipitation will fall as rain, however persistent northeasterly
flow up the Saint Lawrence Valley will likely keep sub-freezing air
locked in across that area. This should result in precipitation
falling as freezing rain in that area during the day on Monday
before temperatures climb above freezing Monday evening. A winter
weather advisory has been issued for Jefferson county to account for
about a tenth to two tenths of an inch ice accretion.

The precipitation will end with the warm frontal passage, as most of
the area south of Lake Ontario emerges into the warm sector by late
in the day. Temperatures will climb into the 40s south of Lake
Ontario Monday, possibly near 50 degrees closer to the Pennsylvania
state line.


Monday night and Tuesday a slowly deepening surface low will track
northeastward across the central Great Lakes and into southern Quebec.
As it does will finish pushing its warm front across our area
Monday night...followed by its trailing cold front later Monday night/
Tuesday morning. Plentiful lift and moisture accompanying the warm and
cold frontal passages will translate into a certainty of widespread
precipitation Monday night and early Tuesday...for which 100 PoPs will
be in play. With a mild airmass in place...the vast majority of the
frontally-driven precipitation will fall in the form of plain rain.
The one exception to this will be across the Saint Lawrence Valley
and northern portions of Jefferson county...where a lingering
northeasterly low level flow of colder air will likely lead to some
additional light freezing rain and ice accumulations of up to a tenth
of an inch Monday evening...before the warm front passes through and
forces a changeover to all rain by Tuesday morning. With this in mind...
a Winter Weather Advisory is in effect through 06Z Tuesday for
Jefferson county. As for temperatures...continued warm advection will
result in early evening lows ranging from the upper 20s to lower 30s
near the Saint Lawrence River to the lower to mid 40s south of Lake
Ontario...with readings then holding steady or rising through most
of the rest of the night.

Following the passage of the cold front...there will probably be
a brief relative lull in the precipitation late Monday night and
Tuesday morning...before the main upper level low/trailing area of
attendant wraparound moisture works across the region and leads to
another round of fairly numerous showers...which will also become
enhanced downwind of the lakes as increasing amounts of upsloping
come into play. Owing to the rather mild start to the day and only
a modest cold air advection regime found behind the front (850 mb
temps likely only dropping to the -4C to -6C range by early Tuesday
evening)...temps on Tuesday will likely remain mild enough to support
all rain through midday areawide...before cooling of the column
allows for a mix/with changeover to wet snow to develop across the
higher terrain of the Southern Tier Tuesday afternoon. Speaking more
specifically with respect to temperatures...daytime highs on Tuesday
will range from the low-mid 40s across the far west to the mid-upper
40s elsewhere...before giving way to falling readings during the

Given expected snowmelt from the milder temperatures/dewpoints and
the expected rainfall...there will be a continued risk of ice jam
flooding through early Tuesday evening...for which a Flood Watch
remains in effect for far western New York and portions of the
Finger Lakes Region.

Tuesday night the core of the upper low and the surface low will
slide northeastward into the Canadian Maritimes and become vertically
stacked. In the wake of this system...a continued westerly to west-
northwesterly low level flow will continue to drag progressively colder
air into our region...resulting in lingering synoptically/orographically-
driven precipitation mixing with and changing to snow areawide as it
winds down...while also allowing for some modest lake enhancement
to come into play east and then east-southeast of the lakes. As it
has appeared for the past couple of days...the latter will be best
east of Lake Ontario where deeper moisture and a longer fetch across
the lake will be in place...while any enhancement from Lake Erie will
likely be hampered at least somewhat by lingering ice cover. At this
point snowfall amounts for Tuesday night do not look to be overly
noteworthy...with nighttime totals likely ranging from an inch or
two in the areas of most favorable enhancement to well under an inch
elsewhere. Otherwise...ongoing cold air advection will send our
temperatures back down into lower half of the the 20s.

Wednesday and Wednesday night the surface low will quickly eject
northeastward across Labrador and out to sea...while expansive surface-
based ridging and drier air will ridge eastward into our region.
While our airmass will remain cold enough to support a lake response
during this period...subsidence and drying attendant to the ridge will
otherwise result in an increasingly hostile environment for the lake
snows...which will result in the activity southeast of the lakes
steadily weakening over time. With a capping inversion of only 3-4 kft
in place along with shortening northwesterly fetch to begin with...
these will be relatively insignificant...resulting in only some
nuisance-type additional accumulations through Wednesday night.
Otherwise conditions will just be largely dry and cold...with highs
in the 20s Wednesday followed by lows Wednesday night ranging from
the single digits east of Lake Ontario to the teens elsewhere.

Thursday and Thursday night the aforementioned ridge will crest
across our region...with continued drying and subsidence squelching
whatever weak lake effect snow showers are left during the day
Thursday...with a quiet and dry night then following for Thursday
night. Otherwise it will remain on the cold side...with highs on
Thursday ranging from the upper teens across the North Country to
the lower to mid 20s elsewhere...and lows Thursday night ranging
from the teens south of Lake Ontario to near zero across portions
of the North Country.


The lack of any significant mid level blocking will support a
progressive flow across the country during this period...and that
usually translates into near to above normal temperatures. In this
case...our temperatures will average WELL above normal with the
mercury averaging as much as 20 degrees above late January normals.
That warmth is coming at a good time for most this is
climatologically the coldest time of the year.

Speaking of of the driving features for the warm up
will be a fairly significant storm system that will lift northward
from the Tennessee Valley. More on this in a moment.

Fair weather will be in place across our region on Friday as an
amplifying progressive ridge will cross the Lower Great Lakes...
while its corresponding surface high will exit our region via New
England. This will strengthen an already established southerly flow
that will increase the warm advection and allow H85 temps to climb
into positive territory by the end of the day. Max temps will climb
a solid 10 deg higher than the previous day as highs will easily
eclipse freezing over the western counties.

After a fair and notably less chilly night...Saturday will feature
an increase in clouds with another 10 degrees being tacked onto the
max temperatures. A fairly strong southerly flow ahead of an
approaching wavy cold frontal boundary will encourage temperatures
in the valleys west of Seneca Lake to reach 50. While clouds will be
on the increase...the bulk of the day will be rain free...especially
for the Finger Lakes and Eastern Lake Ontario regions.

The guidance packages diverge in their solutions Saturday night and one camp is stubborn at phasing the sub tropical and
polar jets...while another camp phases the jets and generates a
slower and deeper surface low. So in lies the problem with the
forecast confidence for Saturday night and Sunday. While there is no
doubt that the second half of the weekend will be stormier...the
start and end times for the steadiest rain are as much as 18 hours
apart given the guidance. Stay tuned.


Low cigs in place at all terminal except KART, with patches of IFR
vsbys in fog due to warm air spreading over our snow pack. The
northward lifting stratus deck will reach KART by 21z. Cigs will
then remain IFR or low end MVFR at all sites into tonight. KJHW will
hold in LIFR/IFR CIGs and VIS through tonight. Some rain showers
likely moving near KJHW during the evening, but becoming more likely
across all of WNY during the late overnight as a warm front lifts


Monday and Monday night...MVFR/IFR with widespread rain.
Tuesday...MVFR/IFR with rain showers changing to snow showers before
ending...then areas of lake effect snow also developing east of the
lakes Tuesday night.
Wednesday...VFR/MVFR with a chance of snow showers.
Thursday and Friday...Mainly VFR.


High pressure reaching across the Eastern Great Lakes region will
promote light winds and wave action on the eastern Great Lakes
through tonight.

Easterly winds will re-freshen on Monday, as a large area of low
pressure tracks from the lower Missouri valley towards the Great
Lakes. Conditions may approach small craft advisory conditions on
the western half of Lake Ontario Monday afternoon into Monday

The low will sweep a cold front across the lower Great Lakes late
Tuesday into Tuesday night, bringing solid small craft advisory
conditions and possible gales to Lake Ontario behind the front
Tuesday night into Wednesday morning.


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

Temperatures climbed into the lower 40s across much of western
New York on Saturday...and while freezing temperatures returned
Saturday night...this allowed the snowpack across the region to
partially `ripen`. This process continued today as the mercury
returned to the 40s from the Finger Lakes region westward.
Temperatures will now remain above freezing into Tuesday
evening...with daytime readings peaking between 45 and 50. 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 Monday afternoon. This potential problem will be
exacerbated by a general quarter to as much as a half inch of
rain Monday and Monday night.

While there will be a risk for ice jam flooding...a less
impressive snowpack...lower temperatures and less rain fall
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.


NY...Winter Weather Advisory from 1 PM Monday to 1 AM EST Tuesday
     for NYZ007.
     Flood Watch from Monday afternoon through Tuesday evening for



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