Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 251539
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1139 AM EDT Wed Apr 25 2018

.SYNOPSIS...
A slowly deepening area of low pressure shifting north along the
East Coast will continue occasional light rain across western and
north-central New York this afternoon. 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.

&&

.NEAR TERM /THROUGH TONIGHT/...
A southern stream upper level trough axis is shifting across the Mid-
Atlantic region near midday with a northern stream trough axis
shifting across Lake Huron. These features will eventually phase
together tonight, supporting the slow deepening of low pressure
lifting from the DelMarVa north into New England into tonight. An
inverted trough extending northwest of this low will work to
continue occasional rain into tonight.

The radar mosaic shows two areas of more concentrated rainfall near
midday. The first is shifting north across the eastern Lake Ontario
region and eastern New York with the second oriented from southern
Ontario province south across the Niagara Peninsula into NW PA. In
between these areas, from the Genesee Valley into the Finger Lakes,
a few hours of dry time will occur this afternoon before the
rainfall across far western NY pivots east across Central into
Eastern NY with the surface trough axis. Temps will top out around
the mid 50s with the rain and cloud cover.

Upper level dynamics become enhanced this evening as phasing of the
two troughs occurs over New York. The surface low will deepen below
1000mb to our east and rain will become moderate from the ROC to the
North Country beneath the leading edge of the trough axis aloft.
Northwest winds west of the low pressure will continue a high
probability for additional rain showers further south and west across
Western NY with wrap around moisture. Total rainfall accumulated
from today into tonight 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 mid to upper 30s
tonight with cold air advection. Areas of fog will again become
possible overnight with saturated low levels.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
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.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
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.

&&

.AVIATION /16Z WEDNESDAY THROUGH SUNDAY/...
Low cigs and periods of rain will continue across the terminals this
afternoon into tonight as a trough of low pressure across western
and central New York becomes absorbed into a deepening surface low
shifting north along the East Coast. CIGS will remain at MVFR/IFR
with VIS lowering to IFR in light to moderate rainfall.

Westerly flow will develop tonight as the surface low shifts from
the Mid-Atlantic into New England. This will allow additional
showers and low clouds to continue in wrap around moisture. Expect
IFR VIS/CIGS overnight with some lifting of CIGS likely Thursday
morning as low level drying begins behind the departing storm
system.

Outlook...

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.

&&

.MARINE...
A relatively weak surface pressure gradient will remain in place
across the Lower Great Lakes this afternoon as surface trough
extends north across the Eastern Great Lakes from a slowly deepening
low lifting north along the East Coast. This will keep generally
light winds and negligible waves in place.

The surface low will continue to deepen tonight as it lifts into New
England with westerly winds freshening tonight 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.

&&

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

&&

$$

SYNOPSIS...HSK/Smith
NEAR TERM...HSK/Smith
SHORT TERM...Hitchcock
LONG TERM...Hitchcock
AVIATION...HSK/Smith
MARINE...HSK/Smith



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