Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 251209

Area Forecast Discussion
National Weather Service Buffalo NY
809 AM EDT Wed Apr 25 2018

A large area of low pressure moving by to our south will continue
occasional light rainfall across our region today. Lingering showers
will then gradually taper off from west to east tonight and Thursday
as high pressure and drier builds across the Lower Great Lakes. Two
more weak systems will bring additional periods of rain showers
Friday and Saturday.


A closed upper level low is located across the Mid-atlantic region
this morning while a northern stream shortwave trough approaches the
Eastern Great Lakes from the Michigan upper peninsula. These
features will eventually phase together late tonight, supporting the
slow deepening of low pressure across the Mid-Atlantic region today.
This low pressure will move northward along the east coast through

Southerly flow aloft has tapped into Atlantic moisture overnight and
widespread light rain has been moving from south to north along with
patchy fog and low clouds. The eastern Great Lakes will experience
multiple rounds of light rain today as the northern stream shortwave
trough approaches the region. Height falls will support the
strengthening of a broad area of low pressure moving from the Mid-
Atlantic region north along the East Coast. As this system lifts
north to about NJ, warm air advection will cut off across Western NY
from west to east as winds become westerly. There will likely be
brief periods of little to no rain during this time however low-
level profiles suggest saturation and therefore drizzle and fog will
likely take its place. Temperatures will slowly climb if not stay
steady in the low to mid 50s today.

Upper level dynamics become enhanced this evening as the northern
stream shortwave trough becomes negatively tilted. Low pressure will
stretch into Upstate NY and rain will become moderate from the ROC
to the North Country as it moves eastward tonight. Northwest winds
behind developing low pressure will move from west to east across
Western NY and the North Country into Thursday morning. Rainfall
amounts will range from a quarter of an inch across the Southern
Tier to three quarters of an inch across the North Country. Low
temperatures will drop into the 30s tonight.


On Thursday a progressive mid level closed low will move from the
east end of Lake Ontario in the morning to New England by late
afternoon, with an associated surface low moving down the Saint
Lawrence Valley. Showers will still be widespread east of Lake
Ontario through early afternoon in the deformation axis to the west
of the surface low. These showers will begin to taper off later in
the afternoon as the deeper moisture and forcing begin to move east
of the area. Farther to the west, a few morning showers across
Western NY driven mainly by moist upslope flow will end by midday,
with some partial clearing developing in the afternoon from west to
east. Expect highs in the mid 50s across lower elevations and around
50 across higher terrain, even cooler east of Lake Ontario where
showers last much of the day.

The showers will end by early Thursday evening east of Lake Ontario.
Otherwise dry weather and clearing skies will prevail Thursday night
as a weak ridge of high pressure builds into the eastern Great
Lakes. Lows will be in the mid to upper 30s in most locations.

By Friday there is some model spread still apparent in guidance with
the handling of a weak low moving northward along the east coast.
The GFS is farther west with this system, allowing showers to spread
into much of the region. The NAM/ECMWF/GEM are all farther east,
keeping most, if not all of the rain across eastern PA and eastern
NY. With the GFS being the outlier solution, have trended the
forecast away from the GFS solution with just low chance POPS along
the eastern edge of the CWA.

By late afternoon another northern stream trough moving through the
central Great Lakes may spread a few showers in Western NY. These
showers will develop across the rest of the area Friday night as the
trough sharpens and crosses the region from west to east.

It will be a little warmer Friday, with highs in the lower 60s at
lower elevations and mid to upper 50s on the hills. Increasing cold
advection will drop temperatures back into the mid to upper 30s for
lows by late Friday night, with lower 40s east of Lake Ontario.


Temperatures will return to well below normal this weekend as a deep
trough becomes established across the Great Lakes and New England.
The base of the trough and associated vorticity maxima will cross
the region Saturday with more showers. Chilly northwest flow will
support some upslope clouds and a few showers Saturday night
southeast of Lake Ontario, possibly lasting into early Sunday east
of Lake Ontario. It may even get cold enough for a few wet
snowflakes to mix in later Saturday night and Sunday morning,
especially across higher terrain. Highs both Saturday and Sunday
will only be in the upper 40s to around 50 in most locations, with
mid 40s on the hills. Lows will be in the 30s both mornings, with
some upper 20s possible in the colder Southern Tier valleys and Tug
Hill region if breaks in the clouds develop.

The cold will be temporary, with a strong warming trend developing
early next week. The trough will be forced to the Canadian Maritimes
by Monday, quickly being replaced by a strong southeast US ridge.
This ridge will pump strong height rises and warm advection into the
Ohio Valley and Great Lakes. Expect highs to be well into the 60s on
Monday, and well into the 70s on Tuesday away from lake influences.
Subsidence associated with the expansive eastern US ridge will keep
both days dry.


Light rain will continue across the terminals today and tonight.
Cigs and Vis will gradually continue to deteriorate as occasional
light rain moves across the terminals and cloud bases lower. Expect
the worst (IFR) conditions to continue across the higher
terrain with MVFR across the lower elevations.

Westerly flow will begin from west to east tonight and cigs and
vsbys will slowly improve. Expect mainly MVFR with IFR across the
higher terrain/KJHW and KART through early Thursday morning.


Thursday...Improvement to VFR with showers ending.
Friday and Saturday...Mainly VFR with a chance of showers.
Sunday...Mainly VFR with a chance of rain or snow showers east
of Lake Ontario.


A relatively weak surface pressure gradient will remain in place
across the Lower Great Lakes a large but poorly organized
storm system will pass by well to the south. This will keep
generally light winds and negligible waves in place.

This system will deepen tonight and winds will freshen into
Thursday. Westerly winds will produce sufficient waves and winds on
the southern and eastern shores of Lake Ontario for Small Craft
conditions into Thursday night.


MARINE...Small Craft Advisory from 9 PM this evening to 8 PM EDT
         Thursday for LOZ043.
         Small Craft Advisory from 9 PM this evening to 5 PM EDT
         Thursday for LOZ042.
         Small Craft Advisory from 11 PM this evening to 11 PM EDT
         Thursday for LOZ044-045.



SHORT TERM...Hitchcock
LONG TERM...Hitchcock
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