Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 301053
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
653 AM EDT Thu Mar 30 2017

.SYNOPSIS...
Low pressure will move slowly across the southern Great Lakes later
today through Friday night before moving off the east coast on
Saturday. This will bring periods of soaking rain to much of the
region from this afternoon 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 TONIGHT/...
IR satellite imagery showing mid/high clouds thickening across
Western NY and the western Finger Lakes early this morning. The
North Country will see a brief period of sunshine near sunrise
before clouds increase there as well in advance of a developing warm
front over the central Great Lakes. Radar imagery showing some
returns over central Lake Erie and NW PA, but surface
observations show little if any of this is reaching the ground
owing to very dry low levels.

High pressure will build slowly east across Quebec today and
tonight, with a ridge extending down into our area this morning and
drifting east across New England later today. Meanwhile upstream low
pressure will move across Missouri today and head towards northern
Indiana by daybreak Friday, with an associated mid level closed low
taking a similar track. A warm front extending downstream from the
surface low will strengthen and move slowly ENE across our area,
with several surges of enhanced warm advection and isentropic
upglide from this afternoon through tonight along distinct warm
frontal segments. The strength of forcing and quality moisture
coming into play support a high likelihood of fairly widespread
precipitation from this afternoon through tonight, with several
embedded periods of moderate precipitation likely. Expect the
leading edge to reach Chautauqua County by late morning or midday,
then spread into the rest of Western NY during the early to mid
afternoon, before reaching the eastern Lake Ontario region this
evening.

Precip type will be just rain for most, with the column and surface
temperatures warm enough to support full melting across the bulk of
the area. The one exception will be east of Lake Ontario, where the
slowly retreating high over eastern Quebec will support persistent
northeast low level flow and supply enough cold air to bring snow
and mixed precipitation into play. Soundings support mainly wet snow
across the bulk of Jefferson and Lewis counties overnight, which
will mix with rain and possibly some sleet by Friday morning
especially closer to Lake Ontario. For most of the area soundings
support a relatively limited risk of freezing rain, 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 some freezing rain potential.
Confidence is still fairly low with this scenario given the very
marginal surface temperatures and small area of concern Friday
morning.

As far as accumulations go, expect a general 1-3 inches of snow
across the lower elevations of Jefferson and Lewis counties with 2-4
inches across the higher terrain of the Tug Hill and western
foothills of the Adirondacks. The snow may clip the NE corner of
Oswego County as well, but the bulk of that county is likely to be
mainly rain. Given the relatively modest snow amounts and fairly low
confidence still on freezing rain potential, have held off on a
Winter Weather Advisory for now.

As far as temperatures go, expect highs today in the mid 40s for
most, with lows in the mid to upper 30s tonight in most areas and
low 30s North Country.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
A widespread soaking rainfall will impact the region through the day
Friday before tapering off, and perhaps ending with a few wet
snowflakes, Friday night into early Saturday morning.

Picking up Friday morning, excellent synoptic dynamics will be in
place for a widespread soaking rainfall. An upper level low will
pivot from the Ohio Valley early Friday to the Mid-Atlantic by Friday
night. This will place the forecast area under a diffluent flow
aloft through the entire day as this upper-level low tracks to our
south. Closer to the surface, a 40 knot low-level jet bring a strong
moisture transport into the region of Gulf of Mexico sourced air.
This air will flow over a stalled surface boundary oriented from
Lake Erie across the Niagara Frontier to the Mohawk Valley. As the
low pressure system evolves eastward through the course of the day,
the best forcing and moisture transport will focus from Rochester
eastward toward the eastern Lake Ontario region. This will result in
moderate to heavy at times rainfall from Buffalo across to Rochester
to eastern Lake Ontario through the morning hours Friday, which will
become more focused toward eastern Lake Ontario by late afternoon
and early evening. South of this best forcing, across the western
Southern Tier, expect rain to be on the lighter side, and perhaps
more showery in nature. Afternoon high temperatures will surge into
the lower 50s for portions of far western NY, while tapering to
around 40 in the North Country on the cool side of the surface front.

By Friday night, the dynamics of the system become a bit more complex
as the surface low starts to redevelop along the coastal front off
of Long Island. Meanwhile the original surface low will move from
western NY toward central NY while weakening with time as the
developing coastal low begins to dominate. As this happens, expect
deformation band of rain, perhaps mixed with some wet snowflakes,
especially over the higher terrain of western NY, to cross the
region from west to east overnight. This will then diminish toward
Saturday morning as it exits through the North Country behind the
decaying original surface low. The best chance for some light snow
accumulations with this deformation band will be across the North
Country, closer to the colder airmass wrapping in behind the system.
A light coating to a couple inches of snow are possible there
Saturday morning. After the soaking rainfall, there will plenty of
trapped low-level moisture and a period of light winds before the
westerlies increase toward Saturday morning, this will likely result
in some areas of fog across the region, with perhaps even some dense
fog across the higher elevations. Low temperatures early Saturday
will be in the mid 30s across western NY to a degree or two either
side of the freezing mark in the North Country.

When including rainfall totals from the start of the event late
Thursday, storm total amounts will likely range from 3/4 to 1 inch
across the western Southern Tier, to 1 to 1.5 inches along the I-90
corridor, and just over an inch in the North Country.

High pressure will build in across the region on Saturday and Sunday
resulting in a drying and clearing trend and moderating
temperatures, making for overall pleasant weather for the weekend.
Sunday will certainly be the best weather of the two days through,
as Saturday we will remain shrouded in the cloud cover as low level
moisture remains trapped under the subsidence aloft. High
temperatures will top out in the 40s Saturday. By Sunday, drier air
will work into the region, with better mixing allowing cloud cover
to break up. This will result in fair weather with high temperatures
in the upper 40s in the North Country to the low to mid 50s across
western NY. Saturday night lows will be in the upper 20s to low 30s,
while Sunday night will range from the upper 20s in the North
Country (closer to the surface high) to the upper 30s in western NY.

&&

.LONG TERM /MONDAY THROUGH WEDNESDAY/...
Mid-range models diverge in their solutions for the beginning of the
work week, bringing higher than usual uncertainty to forecast Monday
and especially Tuesday. Forecast models are in decent agreement that
a southern stream wave will track from the central plains to off the
southeast coast by Tuesday, with some minor deviations in strength
and track. However, the larger problem in the models is the
difference in the northern stream wave which simultaneous tracks
from near Montana to the Great Lakes. The GFS remains stronger with
this north stream wave, and allows for some interaction with the
southern stream wave, while the EC remains weaker with the northern
stream wave. This difference result in solutions that vary from a
potential soaking rainfall event Monday night into Tuesday per the
GFS solution or a few passing showers Monday, but overall dry into
Tuesday per the EC solution. Given the continued differences in the
models, have tempered the previous forecast to be a bit more
conservative, with just chance rain showers mentioned for now.
Either way temperatures would remain mild, in the upper 40s to mid
50s, slightly cooler under wet conditions, and slightly warmer under
dry conditions.

Despite forecast uncertainty early in the week, confidence returns
by mid-week in high pressure building in across the region with a
stretch of fair weather through mid-week with mild temperatures.
Forecast models are also in decent agreement on another wet period
of weather for the end of next work week, with a strong low pressure
system tracking from the central plains to the Great Lakes.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
High pressure will build east across Quebec this morning with a
ridge extending down into NY. This will support a continuation of
VFR conditions with high clouds thickening and lowering into a mid
level deck from west to east through midday. Increasing warm
advection ahead of a warm front will allow rain to develop across
Western NY during the afternoon, with rain then spreading east into
Central NY by evening. Expect CIGS/VSBY to remain VFR for the first
few hours of rain as the low levels remain unsaturated. 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 CIGS and MVFR to IFR VSBY across
Western NY with low stratus and ongoing light rain.

Across the North Country the airmass will be colder, and likely
support wet snow tonight including KART with IFR VSBY. The snow will
gradually change to rain close to Lake Ontario Friday morning, with
some wintry mix possible farther east across the higher terrain.

Outlook...
Friday and 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 and Monday...VFR.

&&

.MARINE...
ENE winds will slowly increase today as low pressure moves towards
the southern Great Lakes. These ENE winds will increase further
overnight on Lake Ontario as the pressure gradient tightens between
the approaching low and high pressure over eastern Quebec. This will
bring Small Craft Advisory conditions to the west half of Lake
Ontario this afternoon 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 develop this afternoon and continue through
Saturday morning across the region. 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 along the Thruway
corridor to 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...
NY...None.
MARINE...Small Craft Advisory from 5 PM this afternoon to 8 AM EDT
         Saturday for LOZ043.
         Small Craft Advisory from 11 AM this morning to 8 AM EDT
         Saturday for LOZ042.

&&

$$

SYNOPSIS...HITCHCOCK
NEAR TERM...HITCHCOCK
SHORT TERM...CHURCH
LONG TERM...CHURCH
AVIATION...HITCHCOCK
MARINE...HITCHCOCK
HYDROLOGY...HITCHCOCK


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