Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 210614
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
114 AM EST Sun Jan 21 2018

.SYNOPSIS...
A warm front will push north across the Ohio Valley today bringing a
chance for light precipitation into Western New York. More
significant rainfall is expected Monday, as a large storm system
tracks into the Central 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.

&&

.NEAR TERM /THROUGH TODAY/...
A cold front is draped along the Saint Lawrence River Valley early
this morning. This front is forecast to only subtlety shift south
today while contributing to lower cloud cover across the North
County with a chance of snow flurries.

An expansive region of low-level stratus is shifting from the Ohio
Valley north and east into Western NY. Moisture profiles depict a
well saturated boundary layer across the Southern Tier into Sunday
morning with some drizzle possible. Overnight temperatures will
generally run in the lower to mid 30s, potentially rising a bit
toward morning as the area of stratus continues to spread into the
region.

Cloudy skies expected through much of today and into tonight. Fog
will also be possible as snow continues to melt. Chances of rain
will increase across Western NY through the day under sustained yet
weak isentropic ascent across the warm front. Temperatures today
should warm generally into the upper 30s to lower 40s despite
extensive cloud cover.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/...
Sunday night and Monday low pressure over Kansas will track north-
eastward to around the Wisconsin-Illinois border...with its attendant
warm front first extending further eastward into our region Sunday
night...then slowly lifting northward to about the New York State
Thruway corridor by the end of the day Monday. Slowly increasing
warm air advection/isentropic lift and deepening moisture out ahead
of the warm front will bring slowly increasing chances for some spotty
light precipitation Sunday night from southwest to northeast...followed
by a round of more widespread light precip on Monday as the warm front
slowly lifts northward across areas south of Lake Ontario. In the
forecast...have reflected this by primarily chance PoPs Sunday night
ramping up to the high likely/categorical ranges on Monday. Projected
model soundings and statistical guidance both suggest that ptype Sunday
night will be primarily rain south of Lake Ontario with more of a
wintry mix across the eastern Lake Ontario Region...before this goes
over to mostly rain during Monday as the atmospheric column continues
to warm.

Compared to yesterday...the guidance packages have come into somewhat
better agreement on the northward progress of the surface warm front...
with most now suggesting that the boundary will make it to about the
New York State Thruway by late afternoon/early evening. Those areas
that do manage to fully break into the warm sector on Monday (i.e.,
the Southern Tier and interior portions of the Finger Lakes) will be
likely to the see the rain temporarily taper off to some widely
scattered leftover showers during the afternoon...along with temps
surging into the upper 40s and lower 50s as a milder southerly flow
becomes established. Meanwhile along and to the north of the boundary...
rain and cooler temperatures will likely continue through the end of
the day...with highs ranging from the mid 40s just north of the front
to the mid to upper 30s near the Saint Lawrence Valley...where a low-
level east-northeasterly flow will remain established.

Monday night and Tuesday the surface low will continue tracking
northeastward across the central Great Lakes and into southern Quebec.
In the process of doing so...it will finish pushing the warm front
across our area Monday night...followed by its trailing cold front
on Tuesday. Plentiful lift and moisture accompanying the warm and
cold frontal passages will translate into fairly high probabilities
for widespread precipitation during this period...and as such have
continued with categorical PoPs. With a mild airmass in place...the
majority of this will just fall as plain rain Monday night into
Tuesday morning...before mixing with and/or changing to wet snow
across the higher terrain Tuesday afternoon as cold advection sets
up in the wake of the cold frontal passage. The one possible exception
to this evolution in ptype will be across the Saint Lawrence Valley
and adjoining portions of the North Country...where the initial
lingering northeasterly flow/colder low level air out ahead of the
cold front could lead to a brief wintry mix Monday night...before
the warm front passes through and forces a changeover to all rain
by Tuesday morning.

As has been pointed out previously...the combination of the above
rainfall and increased snowmelt from higher temperatures and dewpoints
will also likely bring about some renewed ice jam-related flood concerns.
While this warm-up is not quite as dramatic as that of last weekend
and overall rain amounts are also likely to be lower given the fast
passage of the cold front...there will still likely be some potential
for ice jam flooding in the Monday to Tuesday time frame...which
remains covered in our Hazardous Weather Outlook product for now.

In the wake of the cold front...a westerly flow of colder air will
continue to deepen across the area Tuesday night. Coupled with a
trailing region of wraparound moisture behind the departing low...
this will bring some scattered snow showers to the area...with some
lake/orographically-driven snows also likely to set up east of the
lakes as the cold air deepens. These will be best organized east of
Lake Ontario...while the Lake Erie activity will likely be hampered
by lingering ice cover. Otherwise...ongoing cold air advection will
send our temperatures back down into the 20s.

Wednesday and Wednesday night the surface low will eject northeastward
across Labrador and out to sea...while expansive surface-based ridging
and drier air ridges eastward into our region. With the building ridge/
drying out of our airmass and winds becoming increasingly northwesterly
over time...the lake-driven snows will weaken and sink southward to areas
southeast of the lakes...while elsewhere scattered snow showers should
continue to diminish in coverage. With a much colder airmass in place...
temperatures will be significantly colder than those of previous days...
with highs on Wednesday struggling to make it above the 25-30 range...
and lows Wednesday night ranging from the single digits east of Lake
Ontario to the teens elsewhere.

&&

.LONG TERM /THURSDAY THROUGH SATURDAY/...
A progressive...Pacific air dominated pattern over the country
during this period will support another significant warming trend.
This will send near normal temperatures on Thursday to levels that
will be some 15 to 20 degrees above normal by Saturday...with
potentially even milder weather possible to close out the weekend.
As is typically the case at this time of year...such a warm up will
be brought to a rather dramatic end by an impactful storm or frontal
passage. This time around...the pattern changing event will be a
deepening storm system that will pass over the region as we
transition from the weekend into the new work week. More on this
storm in a moment.

As we open this period on Thursday...an expansive area of high
pressure will approach our region from the Upper Great Lakes. While
a wealth of dry air and increasing subsidence will provide fair
weather across the majority of the forecast area...a cold northwest
flow ahead of the system will still generate some nuisance lake snow
showers southeast of Lake Ontario. Temperatures Thursday will be
similar to those from the day before with highs generally in the
upper 20s in the west and within a few degrees of 20 across the
North Country.

The axis of the surface high will cross over our region Thursday
night. This will bring an end to the lake snow showers while also
providing us with the last cold night before the warm up. The
mercury will drop into the single digits east of Lake Ontario while
mins will be in the teens to near 20 over the western counties.

As the surface high exits to our east across New England on
Friday...warm advection will begin in earnest as a southerly return
flow will become established. H85 temps moderating to around zero c
will combine with partial sunshine to allow our max temps to jump by
at least 10 degrees from those of Thursday. Some sites west of the
Finger Lakes could even reach 40.

The warming trend will continue Friday night and Saturday as the
southerly flow will intensify ahead of a wavy cold frontal boundary.
This will encourage the mercury to climb well into the 40s on
Saturday...with 50 degree readings not out of the question for parts
of the Genesee Valley and for some of the valleys of the Southern
Tier.

Looking ahead outside of the scope of this forecast package...the
frontal boundary is expected to stall over our forecast area late
Sunday/Sunday night as a result of an intensifying storm system in
the vcnty of the Lower Mississippi Valley and Tennessee Valley. Since
our region will still be firmly ensconced within a warm sector...the
approaching storm will only strengthen the southerly flow...nearly
assuring that the vast majority of the associated precipitation
will be in the form of rain. While the heaviest rainfall should stay
to our south and east...its not out of the question that this system
could generate an inch or more of rain later Sunday through Sunday
night. Colder air will then pour back into the region in the wake
of the storm system on Monday...changing the precipitation to snow
showers while also providing us with some gusty winds.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
MVFR cigs in place KART and KJHW early this morning. Satellite shows
an extensive deck of MVFR low clouds across the Ohio Valley is
spreading north into western NY overspilling a warm front. The
stratus deck will move north to BUF, KIAG and then KROC through
the mid to late morning reaching KROC by early afternoon. KJHW
should lower to IFR by late morning. Cigs will then remain MVFR
at all sites into tonight except KJHW will remain at IFR. 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 north.

Outlook...

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...Mainly VFR.

&&

.MARINE...
High pressure reaching across the Eastern Great Lakes region has
allowed winds to relax early this morning with small craft
advisories cancelled.

Northeasterly winds will re-freshen on Monday, as a large area of
low pressure tracks from the lower Missouri valley towards the Great
Lakes. This will likely generate more small craft advisory
conditions on the western half of Lake Ontario. This low will then
track across the Great Lakes on Tuesday, sweeping a cold front
across the lower Great lakes late Tuesday into Tuesday night and
bringing a potential for gales on Lake Ontario behind the front
Tuesday night into Wednesday morning.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.

&&

$$

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



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