Area Forecast Discussion
Issued by NWS Buffalo, NY

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909
FXUS61 KBUF 212124
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
424 PM EST Sat Jan 21 2017

.SYNOPSIS...
Mild conditions will persist through Sunday. A complex area of low
pressure will then move northward along the east coast early next
week. This system will spread rain into the area Monday, which may
change to wet snow late Monday into Tuesday as colder air filters
into the region. A return to more typical mid winter cold and snow
is expected to arrive late next week.

&&

.NEAR TERM /THROUGH SUNDAY/...
Weak ridge builds over the region tonight. This will reinforce the
low level inversion overnight. The strengthening inversion and
remaining low level moisture will continue to support low stratus,
which will likely expand again overnight. Expect fog and drizzle to
return as well, but do not expect conditions to be a low as they
were this morning. The most widespread fog and drizzle likely to be
found across higher terrain and near the lakes. The mild conditions
continuing through tonight with most overnight low temperatures in
the lower to mid 40s in most locations, with upper 30s across the
North Country.

A significant trough will begin to emerge from the desert southwest
this evening, making its way across the southern plains and Gulf
coast states/Tennessee Valley by the end of the period. Remaining
low clouds and fog/drizzle will diminish Sunday morning with mid and
high level clouds overspreading the area, with a bit more thickening
in the afternoon from south to north. Temperatures will respond
nicely in a strengthening warm air advection pattern with most highs
in lower to mid 50s, with 40s across the North Country. Deeper layer
moisture arrives late in the day Sunday with leading edge of
associated precipitation possibly making it as far north as the
Southern Tier by the end of the day.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
A storm system will bring an assortment of weather conditions this
period, with uncertainty still remaining to precipitation type
through a portion of the period.

This afternoon a pacific shortwave riding through the southern
jet stream is found on water vapor imagery over the dessert
southwest. This feature, including a 1.5 PV anomaly down to nearly
600 hPa, will develop a surface low that will cross the SE states
early next week, and eventually lift northeastward along the mid-
Atlantic and New England coastline. This impressive storm system
will pull moisture from both the Gulf of Mexico, and Atlantic to
spread abundant moisture over the Eastern Great Lakes region.

For our region Sunday night a strong easterly flow will maintain
mild temperatures across our region, this from a large area of high
pressure over eastern Canada, and the storm system that will be
passing through the Tennessee Valley. This flow will maintain
temperatures in the lower 40s near Lake Erie, with mid to upper 30s
found elsewhere. Initially there will be a mid level dry wedge that
increasing moisture will need to overcome before we start to see
precipitation reaching the ground. As moisture increases through the
night, we will have chance pops increasing from south to north
across WNY, while the Eastern Lake Ontario region will likely remain
dry. Thermal profiles suggest that falling precipitation should
remain as all rain through the night, and into Monday morning.

Monday there is still a bit of model uncertainty as to how far north
the upper level low, and its associated cold pool reach, with the
12Z GFS and 09Z SREF a bit farther northward than the 12Z ECMWF and
12Z Canadian models. Thermal profiles continue to indicate marginal
cooling through the lower atmosphere, and it may very likely be
dynamical cooling as the upper level low nears that will change
precipitation over to plain snow through the day Monday and into
Monday night.

The initial slug of deeper moisture, and lift within a trowel
signature will come earlier in the day Monday, and the change over
to accumulating snow may not be until later in the day Monday and
Monday night when the bulk of the deeper moisture will have passed.
Will continue to indicate a change over to a wintry mix (sleet and
snow) and then all snow by Monday night, though overall snow totals
are still very uncertain. If the change over to snow occurs sooner
we could see several additional inches of snow. A look at CIPS
analogs, the higher percentage of measurable snowfall of 6 inches
plus through Monday evening lies across the higher terrain of the
Finger Lakes and Eastern Lake Ontario region which will be closer to
the influences of the trowel signature. It seems reasonable that
this event will produce the greatest snowfall totals (still very
uncertain) across the higher terrain of the Finger Lakes and Eastern
Lake Ontario region.

Will continue with likely pops Monday night as wrap around moisture
and CAA brings an additional likely period for light snow. As the
upper level low exits off the New England coastline Tuesday
precipitation chances will diminish from west to east through the
day and evening. A mid level ridge axis will cross the region early
Tuesday night, with a likely dry period, before another upper level
low, this time in the northern branch of the jet stream nears the
region late Tuesday night with a mix of rain and snow.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
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 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. 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 snow 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 would be the most likely areas to see the most
snow.

&&

.AVIATION /22Z SATURDAY THROUGH THURSDAY/...
Abundant low level moisture continue to support widespread IFR in
low stratus close to Lake Ontario from KIAG-KROC-KART north of a
warm front. VFR conditions area expected south of these sites
through the rest of the afternoon. KIAG and KROC may briefly
go VFR late this afternoon and early this evening.

Abundant low level moisture will remain in place tonight, and a
steepening low level inversion and nocturnal cooling will likely
allow stratus to expand again tonight. Expect a return to more
widespread IFR after 03Z Sun, with areas of fog and drizzle also
forming again and bringing IFR VSBY overnight. Conditions again
appear favorable for CIGS and possibly VSBY to drop to near airfield
minimums at times overnight, especially across higher terrain and
near the lakes.

Outlook...

Sunday...Areas of IFR/MVFR in low stratus, fog, and drizzle.
Monday and 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.

&&

.MARINE...
A weak pressure gradient will maintain light winds at less than 15
knots through Sunday morning. Low pressure will then develop and
move slowly north along the east coast early next week, while high
pressure remains parked over Quebec. The increasing gradient between
the two will bring stronger northeast winds to the Lower Great Lakes
late Sunday through Tuesday, with winds peaking Monday and Monday
night. This will likely bring higher end Small Craft Advisory
conditions to the lakes early next week.

&&

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

&&

$$

SYNOPSIS...TMA
NEAR TERM...TMA
SHORT TERM...THOMAS
LONG TERM...APFFEL
AVIATION...TMA
MARINE...TMA



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