Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 221837

Area Forecast Discussion
National Weather Service Buffalo NY
137 PM EST Sun Jan 22 2017

Warm and moist conditions will last through tonight with above
normal temperatures and some light rain showers or drizzle. Then low
pressure developing across the Southeastern states will move to
the mid-Atlantic on Monday and then into Southern New England on
Tuesday. This will bring rain and wet snow into our region with
potentially significant snow accumulations in some areas.


For the remainder of today, the region will remain between high
pressure to the north, and low pressure developing across the
Southeastern states. The high will help maintain a northeasterly
flow across the Niagara Frontier, which will strengthen with time.
This will maintain a cool and moist flow off Lake Ontario with
areas of fog and drizzle expected to last much of the night. This
is probably best captured by the HRRR which has been handling this
fog and stratus fairly well over the past couple days.

Otherwise, an area of showers near Buffalo has not been well
captured by guidance. Following a weak 700 mb flow, expect these
showers to very slowly drift northeast this afternoon before
dissipating this evening.

Temperatures will vary this afternoon, with much warmer conditionsacross
the Western Southern Tier where a few breaks of sunshine have
allowed readings to climb into the upper 50s. Temperatures should
top out in the mid to upper 40s south of Lake Ontario where
stratus and fog will remain in place. For tonight, expect lows in
the upper 30s to lower 40s.

Low pressure will creep closer to our region, with a chance of
showers across the Southern Tier late tonight. A consensus of 12Z
guidance is slower than previous runs, so timing has been delayed
to account for this.


The main focus through the short term period will be on a strong and
complex storm system moving up the east coast Monday afternoon
through Tuesday. Model guidance continues to show run to run
variation and poor agreement between various models on the important
details of the track and strength of the upper level features and
thermal profiles, which is resulting in below normal forecast
confidence on the placement of best snow potential.

A strong southern stream mid level trough will move through the
southeast states Monday, then swing up the east coast and take on a
negative tilt Monday night and Tuesday. At the surface, a strong low
will move across the southeast states Monday, with secondary coastal
cyclogenesis near the triple point just east of the Outer Banks
Monday evening. The ensuing coastal low will then rapidly deepen and
move NNE, along or just offshore of the east coast, reaching the
Gulf of Maine Tuesday night. Meanwhile a strong high will remain in
place over eastern Quebec, with the gradient between the two forcing
a strong easterly low level jet to develop to the north of the
surface low, with a plume of deep Atlantic moisture streaming inland
and into our region.

The strongest dynamics will move into the Southern Tier Monday
afternoon, then move north across the rest of the area through the
first half of Monday night. The nose of the strong easterly low
level jet will cross our region, enhancing low level convergence and
moisture transport. Meanwhile aloft, strong upper level divergence
will develop in the left exit region of a 120 knot upper level jet
by Monday evening, further enhanced by a strongly diffluent upper
level flow pattern to the north of the potent closed low over the
Mid Atlantic. The strong forcing coming together will produce a
period of deep layer ascent crossing the region from south to north
later Monday afternoon and Monday night. High quality moisture will
be available with over 4g/kg specific humidity near the 700mb layer.
The strong dynamics and deep moisture will allow for a 4-8 hour
period of moderate to heavy precip across the area.

While confidence is high on a period of heavy precip, the timing of
the various PTypes remains uncertain given model differences on the
low and mid level thermal structure. Model guidance continues to
show the system capturing an area of slightly colder air from the
airmass associated with the surface high over eastern Quebec. This,
combined with cooling from evaporation, melting, and strong ascent,
will force the column to become isothermal near or just below the
freezing mark once the heavier precip begins.

As precip arrives during the first half of Monday, many areas will
still be warm enough for just light rain. As precip rates increase
during the afternoon, expect the higher terrain of the interior
Southern Tier to change to wet snow, with this change then advancing
north during the late afternoon and evening. 00Z model consensus
suggests the best area for an extended period of all snow will be
from the Genesee Valley into the western Finger Lakes, where the
greatest risk of moderate to marginally heavy accumulations is
found. Farther west across the Niagara Frontier and near Lake Erie,
the GFS based guidance suggests a longer period of mix or rain as a
warm layer persists, with a similar trend east of Lake Ontario. This
event bares some resemblance to the March 30, 2014 heavy snow event
which dropped a narrow area of heavy snow on the Genesee Valley and
Western Finger Lakes.

Precip rates will diminish by late Monday night and early Tuesday as
the stronger dynamics move north and away from the area. A second
period of stronger ascent may move north through the eastern Lake
Ontario region during the day Tuesday as a deformation axis develops
on the western flank of the system moving northward along the east
coast. Both the GFS and NAM suggest a warm layer lingering aloft
during this period however, which may bring a wintry mix east of
Lake Ontario and possibly hold snow amounts down. Farther west, the
column should be cold enough for mainly snow, but amounts should be
light from the Finger Lakes into Western NY with stronger dynamics
and deeper moisture remaining farther east.

We considered going with a Winter Storm Watch for a portion of the
area from roughly the Genesee Valley eastward, but given the
continued model differences confidence is just not there yet to
refine the details of placement of heavier snow amounts. Our first
cut at storm totals range from 4-6 inches across lower elevations of
the Genesee Valley and western Finger Lakes and portions of the
eastern Lake Ontario region, with higher amounts of up to 8 inches
across the highest terrain. These numbers will likely change in both
amount and location as model guidance converges on a common solution.


In general, model consensus for the long term period is in good
agreement. Temperatures will start off above average, but will
gradually cool to a more seasonable mid-winter pattern with
increasing chances for lake effect snow.

On Wednesday morning, a narrow ridge axis will extend up the Eastern
Seaboard while low pressure tracks across the Central Great Lakes
Region. A warm front associated with this low will likely bring some
showers which will start off as rain or wet snow but trend to all
rain as temperatures warm. This will be followed by an ill-defined
cold front and surface trough which will move across the region
Wednesday night and bring more showers, which will mix with wet snow
overnight as weak cold advection begins. Outside of the showers,
Wednesday should be a warm and breezy day with highs in the 40s.

A gradual cooling trend will begin after this, with thermal profiles
marginally cold enough to support a mix of wet snow and rain on
Thursday. Cold air advection will continue with any precipitation
likely to be all snow by Thursday night through the weekend.
Precipitation will mainly be from upsloping and residual moisture on
Thursday with 850 mb temps running -4 to -6C there will not be any
lake induced instability.

The pattern becomes more favorable for lake effect snow late in the
week and going into the weekend. The mean flow will be westerly,
however winds will meander some during this time with the passage of
any shortwaves. The most significant one is likely to come Friday
night or Saturday, though model consensus differs slightly on the
timing. By this time, there should be some lake induced instability
but more importantly the moderately strong flow should will likely
run down the length of the lakes which will provide favorable
conditions for snow bands to develop. Uncertainty in wind direction
makes it difficult to pin down exact locations, but in general the
typical snow belts east of the lakes would be the most likely areas
to see the most snow.


At 18Z, there was VFR conditions in place across most of Western
New York with the exception of areas south of Lake Ontario which
includes the BUF/IAG/ROC terminals. This is because the northeast
flow is pushing cool and moist air off the lake into an area of
higher dew points which is helping maintain LIFR cigs and areas of
fog. Some showers may help improve conditions briefly this
afternoon at these sites, but an increasing northeasterly flow
should push fog back into these terminals early this evening.
Expect IFR or lower conditions to continue at these terminals
most of the night with areas of drizzle and fog. There continues
to be a potential for dense fog, though it is lower tonight
because of the stronger flow which will provide better boundary
layer mixing.

Otherwise, expect mainly VFR conditions to continue until this
evening when low moisture spreads into the Southern Tier and
lowers conditions at JHW. In terms of guidance, TAFS are fairly
close to a blend of HRRR and NAM BUFKIT guidance.

On Monday, rain will gradually spread from south to north during
the day as low pressure tracks into the mid Atlantic.
Precipitation will start as rain, but may mix with wet snow in
spots toward sunset Monday evening. Expect mainly IFR/MVFR
conditions as this precipitation moves in.


Monday night...Areas of MVFR/IFR with rain changing to wet snow.
Tuesday...Areas of MVFR/IFR with wet snow mixed with rain.
Wednesday and Thursday...VFR/MVFR with a chance of rain and snow.
Friday...VFR/MVFR with a chance of snow showers.


Easterly winds will increase across Lake Ontario and Erie through
tonight as we get caught between high pressure over Quebec and a
deepening low pressure system moving into the Mid Atlantic. Small
craft advisories have been issued for the western half of Lake
Ontario as the east- northeasterly winds strengthen to 20 to 25
knots. Winds and waves will remain elevated until the low pressure
system passes on Tuesday. Lake Erie remains less of a concern as
wave action will directed away from the eastern end of the lake.


MARINE...Small Craft Advisory from 7 PM this evening to 1 PM EST
         Tuesday for LOZ042-043.



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