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Area forecast discussion
National Weather Service Buffalo New York
316 PM EDT Thu Mar 30 2017

Synopsis...
low pressure over Illinois will move slowly south of the Great Lakes
through Friday night before moving off the East Coast on Saturday.
This will bring periods of soaking rain to much of the region
through Saturday morning, with snow and mixed precipitation across
the north country. Mainly dry weather will return later Saturday and
Sunday as high pressure builds into the eastern Great Lakes.

&&

Near term /through Friday/...
radar imagery showing the leading band of precipitation oriented
along an elevated warm front is moving northeast across western New York
this afternoon. Bright banding is displaying higher precip rates
than what are actually being recorded at the ground based on checks
of mesonet gauges. Evaporative cooling of the lower atmosphere where
the higher returns are being picked up is causing surface temps to
lower and dewpoints to rise with some locations and mesonet cameras
across the southern tier and far southtowns seeing some wet snow
occuring before a changeover to rain should occur.

A 50-kt low level jet will continue to transport moisture across the
warm front resulting in widespread precipitation while the front
shifts to the north and east across western New York and The Finger lakes
through the balance of the afternoon reaching the Eastern Lake
Ontario region by nightfall. In a similar fashion to what has
happened earlier this afternoon, expect evaporative cooling to allow
for some areas of wet snow to occur before a changeover to rain.
This is especially possible across the Genesee Valley and western
Finger Lakes into the evening. Any snow accumulations would be
limited to a few tenths of wet snow. Rainfall accumulations of a
tenth to a quarter of an inch are possible.

Tonight, widespread precipitation is expected as the surface warm
front extends across western and central New York. Precip type will
be plain rain for most of western New York and The Finger lakes, with low
level temperatures warm enough to support full melting across the
bulk of the area. There may even be a few periods of moderate to
heavy rainfall overnight along the front. The exception will be east
of Lake Ontario, where the warm front will stall just short of
tonight, supporting persistent northeast flow supplying enough low
level cold air to for snow and some mixed precipitation. Forecast
soundings and sref plumes support mainly wet snow across the bulk of
northern Oswego, Jefferson and Lewis counties, which will mix with
some sleet and freezing rain at times with a thin layer of warm air
laying over the cold surface temperatures. For most of the area
soundings support a relatively limited risk of freezing rain and
sleet, with the one possible exception of southern Lewis County. In
this area, the warm nose aloft may arrive several hours prior to
surface temps moving above freezing, setting the stage for a little
higher freezing rain potential. Sref probabilities for freezing rain
and sleet across the North County run less than 10 percent. Low
surface temps will dip into the low to mid 30s in most places with a
warm nose aloft likely preventing any change to snow in western New York
south of the front.

Through Friday, the warm front extended generally along the Southern
Lake Ontario shoreline in the morning will slowly lift northeast
across the north country. South of the boundary as it moves expect
more plain rain with temps only warming into the low to mid 40s.
North of the boundary expect wet snow with some sleet and freezing
rain possible until the warm front lifts north to the Saint Lawrence
River valley. Total liquid quantitative precipitation forecast through tonight and Friday will run
between one and one and a half inches with highest along the
Southern Lake Ontario shoreline. Closer to a half inch toward the
western southern tier. See hydrology section below for more info on
impacts from this rain.

On the cold side, have posted a Winter Weather Advisory for the
Eastern Lake Ontario region starting at 8pm tonight and running to
8pm Friday to cover for 3-6 inches of wet snow with up to a tenth of
an inch of ice possible from mixing in of sleet and freezing rain at
times. These higher amounts will be mainly across the higher terrain
surrounding and including the tug.

&&

Short term /Friday night through Sunday night/...
it will be a soggy start to the weekend...as rainy weather from
Friday will continue into Saturday morning. The Dismal weather will
be provided by a slow moving...complex storm system that will have
its upper level support pass across Pennsylvania. Meanwhile...at the
surface...a weak sfc reflection will 'transfer' its energy to the
New Jersey coast where a more significant low will take shape. This
will mean that the bulk of the dynamics associated with this mature
system will move east of our region...with only the semblance of a
weak deformation zone trailing across the far western counties. The
result will be some light rain and possibly some drizzle for most
areas...although the pcpn could mix with or change to a little wet
snow for sites east of Lake Ontario. Given the light sfc gradient
and near saturated conditions...there should be some fog as well...
with dense fog possible over the higher terrain.

While mid level ridging will make its way across the lower Great
Lakes on Saturday...guidance is suggesting that an inverted trough
will extend back across our region from the newly formed coastal
low. This will maintain a cyclonic flow in the low levels so that
the wealth of residual moisture (trapped beneath a subsidence
inversion) will keep much of the day shrouded under clouds. There
will even be some leftover showers during the morning...especially
east of the Genesee Valley where low level convergence near and head
of the inverted trough will offer some lift. Early morning probability of precipitation will
range chc over the far western counties to categorical from the Tug
Hill to the foothills of the Adirondacks. Temps Saturday afternoon
will generally be in the low to mid 40s.

A shortwave in the northern branch will sweep across the St Lawrence
Valley Saturday night...glancing by our forecast area in the
process. While there will still be a fair amount of low level
moisture in place...high pressure nosing south from Hudson Bay
should supply US with fair dry weather. Temps Saturday night will
generally settle into the upper 20s to lower 30s.

Ridging moving across the lower Great Lakes will supply US with a
nice ending to the weekend...as at least partial sunshine and 850 mb
temps near zero c will enable Sunday afternoon temperatures to get
into the 50s (up 40s ern lake ont region).

&&

Long term /Monday through Thursday/...
a progressive...low amplitude pattern at the start of this period
will become phased with significant amplification as we push into
the second half of the week. This will lead to a period of cold
weather just beyond this forecast period...one that will feel more
like early March rather than early April. In the process of this
pattern change...a pair of southern stream storm systems will pass
over or just south of the region. In terms of the day to day
details...

The first of the southern stream storms will make its way to the
lower Ohio Valley by late in the day. Clouds will thicken over our
forecast area in the process...with some showers possibly starting
over the western counties during the afternoon. 850 mb temps warming to
near 5c from The Finger lakes west to Lake Erie would support
afternoon Max temps in the mid 50s.

The broad storm system will pass across the mid Atlantic region
Monday night and early Tuesday...with rain becoming a little more
widespread over our region. This will especially be the case over
the southern tier.

As this storm system pulls away Tuesday afternoon and night... a
passing mid level ridge will support a brief period of dry fair
weather.

Unsettled weather will return late Wednesday into Thursday as the
next system will take aim on the lower Great Lakes.

&&

Aviation /19z Thursday through Tuesday/...
mix of MVFR/VFR conditions continue across western New York with a warm
front shifting north and east. The MVFR is occuring in the rain and
wet snow along the front. By this evening the low levels will
saturate, and a low level frontal inversion will steepen, further
trapping low level moisture and increasing the likelihood of IFR
ceilings and MVFR to IFR visibility across western New York with low stratus and
ongoing rain which will persist into Friday afternoon.

Across the north country the airmass will be colder supporting wet
snow later in the evening including kart with IFR visibility and
eventually ceilings. The snow will be slow to gradually change to rain
Friday morning, with some wintry mix possible farther east across
the higher terrain.

Outlook...
Friday night...MVFR/IFR with rain. A wintry mix possible across
the north country.
Saturday...MVFR/IFR with showers in the morning, improving to
MVFR/VFR in the afternoon.
Sunday...VFR.
Monday and Tuesday...chance of rain with MVFR possible.

&&

Marine...
east-northeast winds will increase further overnight on Lake Ontario as the
pressure gradient tightens between an approaching low and high
pressure exiting over eastern Quebec. This will bring Small Craft
Advisory conditions to the west half of Lake Ontario through Friday
evening. Winds will become north and diminish late Friday night and
Saturday morning as the low moves off the East Coast.

&&

Hydrology...
periods of rain will shift north and east across western and
central New York through Saturday morning. Expect long duration light
rain, with several embedded periods of moderate to briefly
heavy rain as ribbons of stronger forcing move across the
region. Event total rainfall amounts look to run from 1-1.75
inches in most areas, with the latest mesoscale model guidance
supporting the highest totals in an east/west band between the
thruway corridor and the South Shore of Lake Ontario.

The rainfall will produce significant within-bank rises on area
creeks and rivers. Mmefs ensemble river forecasts suggest a
relatively low chance of minor flooding for the Buffalo creeks
as well as Black Creek and Oatka creek. Given the rain is spread
out over a few days and the relatively low chance of river
flooding, will hold off on a Flood Watch. If the heavier axis of
rain ends up being a little farther south and over the
headwaters of the creeks mentioned above, the risk for minor
flooding would increase in those creeks.

&&

Buf watches/warnings/advisories...
New York...Winter Weather Advisory from 8 PM this evening to 8 PM EDT
Saturday for nyz006>008.
Marine...Small Craft Advisory until 8 am EDT Saturday for loz043.
Small Craft Advisory until 8 am EDT Saturday for loz042.

&&

$$

Synopsis...Smith
near term...Smith
short term...rsh

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