Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 150225

Area Forecast Discussion
National Weather Service Buffalo NY
925 PM EST Wed Feb 14 2018

A southerly flow will continue to provide Western New York with a
warming trend through Thursday. The result will be some fog and
drizzle due to the warm air over the snowpack. A warm front will
move in later Thursday with chances of rain showers increasing
during the afternoon and evening. A cold front will cross our
region Thursday night with rain changing to snow Friday, followed
by cooler weather for the weekend.


Low level warm advection along with a strengthening low level jet
over the Ohio Valley will bring large area of low clouds and fog
ENE across the region overnight as noted through upstream
surface observations and GOES16 Nighttime Microphysics RGB. The
warm airmass over snowpack together with dewpoints that will
rise above freezing under the cloud deck will also promote fog
development and some drizzle as well. Areas north of the
approaching cloud mass should get to or below the freezing mark,
but expect temperatures to start rising again with the warming
airmass under the blanket of clouds.

Thursday, low pressure moving east across the Northern Great
Lakes overnight will be north of NY Thursday. A warm front
associated with this low will move into the state, supporting
temperatures in the 50s for most locations south of Lake
Ontario. Southwest winds 15-25 gusting up to 35 mph east of the
lakes will keep the lake shores in the 40s with the interior
North County also topping out in the 40s. The winds should
remove any fog that formed overnight, although mesoscale
guidance indicates some fog may hold downwind of Lake Erie
possibly into Buffalo. Otherwise, look for mainly dry weather
until chances for rain increase late in the day ahead of a cold


On Thursday night weak low pressure will track along a frontal
boundary which will bring a period of rain to the area, especially
southern portions. Although temperatures will fall Thursday night,
warm temperatures from Thursday will linger into Thursday evening,
resulting in significant snow melt across much of the region. This
combined with the rain will pose a risk for flooding across Western
New York. The key forecast challenge is rainfall amounts, with model
QPF in overall poor agreement for Thursday night due to the subtle
nature of the driving feature. Model consensus suggests precipitation
amounts will range from about a half inch near the New York/Pennsylvania
border, down to about a tenth of an inch across the North Country.
However there is a wide spread in guidance with higher (or
lower) amounts are possible. Based on this risk a Flood Watch
was issued for most of Western New York from Thursday afternoon
through Friday afternoon. For more on this, read the hydrology

Colder air will build rather quickly into the region Friday morning,
with any lingering precipitation quickly changing from rain to snow
during the morning hours. Although steady precipitation should end
as the weak surface low moves into Southern New England there will
be a secondary cold front which drops across the North Country around
mid-day. This will coincide with the passage of an upper level
trough, which can be an environment favorable for snow squalls. Then
following this colder air will move across Lake Ontario supporting a
brief period of lake effect snow southeast of the lake Friday
evening which will taper off late Friday night as winds diminish.
Otherwise, expect highs to be during Friday morning with
temperatures falling into the 20s Friday afternoon. Temperatures
will fall into the teens in most areas Friday night, with lows
likely to be near zero across the North Country where good
radiational cooling conditions should develop late in the night.

On Saturday, high pressure across New York in the morning will move
across New England in the afternoon. This will result in dry weather
during the day with increasing clouds late in the afternoon in
advance of the next system. After this, model consensus tracks low
pressure to our south and into the Mid Atlantic region Saturday
night. Some guidance (notably the GGEM) clips Western New York with
some light snow while other keeps the area dry. Based on this will
maintain a chance of snow. Either way, the snow would be light,
having little overall impact.


On Sunday...another large area of high pressure and much drier
air will quickly ridge across our region in the wake of Saturday
night`s pair of systems. This will result in a dry and quiet day
for our region...aside from the outside chance of a few leftover
orographically-driven rain and snow showers across the North Country.
Meanwhile high temperatures will range between the mid 30s and lower
40s...or a little above average. Fair and dry weather should then
continue through Sunday night as the high slides out across New
England...with developing warm air advection on its backside driving
at least some increase in mid and high cloud cover along with a
non-diurnal temperature trend...with evening lows in the mid 20s
to lower 30s giving way to rising readings overnight.

Moving on into next week...a significant shift to a period of milder
and wetter weather still appears to be in store for at least the
first half of next week...if not a little bit longer. The impetus
for this change will be provided by a deepening longwave trough
across the western half of North America...which will help encourage
the significant amplification/northward expansion of subtropical
ridging across the eastern CONUS. As a result of these developments...
increasingly milder GOMEX-based air will be pumped northeastward
across the eastern half of the country...resulting in both rising
temperatures for our area as well as the development of a strengthening
baroclinic zone extending from the central and southern Plains states
northeastward to the Great Lakes and southern Ontario/Quebec Provinces.
Several pieces of energy ejecting from the longwave trough will ride
northeastward along this frontal zone and force the development of
one or more attendant waves of low pressure that will pass by to our
northwest...thereby enhancing the influx of milder air/moisture and
bringing periodic opportunities for (mostly) rain showers to our
region in the process.

With the above in mind in conjunction with the usual variances seen
amongst the models this far out in advance...for now have simply
broadbrushed high chance to lower-end likely PoPs for showers in the
Monday-Wednesday time frame...and have maintained well above normal
temperatures in the 40s/50s by day and the mid 30s to lower 40s at
night. This is definitely not out of the question that we
could get even warmer than this Tuesday and/or Wednesday should some
of the warmer model guidance (most notably the consistently warm
ECMWF) manage to verify...stay tuned.


VFR conditions will be replaced by widespread MVFR and IFR
conditions as extensive low clouds and some fog move into the
region from the Ohio Valley. Some drizzle is also possible. Fog
will be most notable where there is snowpack.

Conditions should linger into Thursday with winds again increasing
during the day and gusting to around 30kts. This should remove most
of the fog except perhaps at KBUF where fog may continue to be
advected off the frozen lake. Widespread rain will move into
WNY toward 00z Friday.


Thursday night...Mainly IFR with rain and fog.
Friday...VFR/MVFR with a chance of snow.
Saturday night...chance of snow and IFR.
Sunday and Monday...Chance of MVFR/IFR with chance of -SHRASN.


High pressure is located off the New Jersey coast this afternoon.
Southwest winds have freshened across the Lower Great Lakes as the
pressure gradient tightens. Southwesterly winds will relax some
tonight. A warm front will shift across the eastern Great Lakes
Thursday. Winds and waves may approach Advisory level during the day
with mixing. Winds look to relax Thursday night as a cold front
begins to shift eastward. Behind the front, elevated winds and
likely advisory level waves are forecast Friday under westerly flow.
Winds/waves are expected to relax this weekend with high pressure
building across the region.


A flood watch was issued for a portion of Western New York for a
risk of both ice jam flooding and river flooding. A period of warm
weather will last through Thursday evening, resulting in a
significant amount of snow melt in the Buffalo Creeks and the
Allegheny River basins. Based on the latest forecast, thawing
degree hours will reach between 350 and 500 in these areas which
suggests there is a risk for ice jams. Ice on the Buffalo
creeks is patchy, but probably minimally ample to support some
issues. Because the ice is relatively thin, ice is likely to
break up rather quickly and also may flush out quickly too given
there will be less ice than earlier in the season. This still
poses a risk for ice jam flooding in the typically vulnerable

Following the warm temperatures, a period rain is expected Thursday
night. There is considerably uncertainty with this aspect of the
event, with a consensus supporting between a quarter and a half
inch. However, there is a significant number of ensemble members and
model runs which suggest there will be more rain, perhaps up to an
inch in the watch area. Expect any basin averages in excess of a
half inch will push forecast points to above action stage or even
flood stage when combined with run-off from snow melt. This
uncertainty is reflected in MMEFS ensemble guidance which shows a
wide range of crest levels based on differences in the QPF.

For the Genesee River basin the risk depends on how much rain
falls and given the uncertainty there is not enough confidence
to issue a watch at this point. Temperatures in the Black River
basin will be cooler and there will be less rain there so a
watch is unlikely to be needed for that basin.


NY...Flood Watch from Thursday afternoon through Friday afternoon
     for NYZ010>012-019>021-085.



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