FXUS61 KBUF 250538

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

A large...slow moving storm system moving by to our south will
bring a period of widespread light rainfall to our region overnight
and Wednesday...with lingering showers then gradually tapering off
from west to east Wednesday night and Thursday as high pressure and
drier builds across the Lower Great Lakes.


Light rain will continue to spread northward across Western NY
late tonight. Dry conditions will come to an end by daybreak
across the North Country as a band of moderate rain moves
northward from I-90.

The responsible area of low pressure over the Carolinas will
continue to pump increasing amounts of Atlantic-based moisture
into our region as it heads toward the mid-Atlantic coastline.
At the same time...modest height falls aloft and a diffluent
upper level flow regime (owing to a weakly coupled upper level
jet) will help to lift this deepening moisture field...resulting
in occasional light rain continuing to slowly spread
northeastward across our region...with the steadier rain finally
reaching the North Country toward daybreak. Total nighttime
rainfall amounts will range roughly from up to a couple tenths
of an inch across far western New York to under a tenth of an
inch east of Lake Ontario...with some patchy fog also developing
overnight as the lower levels moisten. This will especially be
the case across the higher terrain (generally >1500') where the
lowering stratus will intersect the ridge tops.

On Wednesday...the southern stream stacked low will continue east to
the Mid Atlantic coast while a robust northern stream shortwave will
approach from the Upper Great Lakes. Earlier guidance suggested that
these two features would phase in time to have an influence on our
weather...but it now appears that they will remain two distinct
features until they move east of our region. In any case...the axis
of the mid level trough between the two will cross our region and
help to focus more light to occasionally moderate rain. The amount
of lift is not forecast to be as significant as that from the
overnight...but there will be more moisture to work with. Will
maintain cat pops with daytime rainfall amounts in the vcnty of a
quarter to a half inch...with the higher amounts expected to be near
and east of Lake Ontario.


On Wednesday night, a closed 500 mb embedded in the northern branch
of the jet will absorb another low across the mid-Atlantic states.
Model guidance differs on the track of this with the 12Z GEM/ECMWF
guidance tracking this low across western New York while the NAM/GFS
guidance is north and faster with its track. The southerly/slower
track would result in more precipitation and have it last a bit
longer. The forecast uses a consensus of guidance with fairly steady
showers Wednesday evening tapering off from west to east overnight.
Consensus 850mb temperatures fall to around 0C which may allow some
wet snow to mix in across the highest terrain in the Southern Tier
but this will not result in any accumulation. Low temperatures will
range from the mid 30s to lower 40s on Wednesday night.

Showers will likely linger east of Lake Ontario into Thursday
morning, but the rest of the area should be mainly dry on Thursday
as a ridge of high pressure builds in from Michigan. As a result the
forecast is a bit warmer with highs in the 50s with a modest lake
breeze developing in the afternoon. High pressure will then briefly
ridge across the region Thursday night with dry weather and lows in
the 30s.

A broad upper level trough axis will gradually shift to the east
coast Friday and Friday night. A broad surface low is forecast to
develop across the mid-Atlantic states on Friday and track into New
England on Friday night. Model guidance differs, but this may clip
especially eastern portions of the cwa on Friday with some light
rain showers possible. Then showers are possible in all areas Friday
night when the upper level trough axis moves across the area.
Rainfall amounts should be fairly light with this, generally under a
quarter inch. Temperatures should be near normal with highs on
Friday in the mid 50s to around 60.


Showers will move through the area on Saturday as an upper level
trough drops from the Great Lakes to the New England coast. With
this trough passage temperatures will also cool to the low to mid
50s for Saturday and Sunday.

Behind the departing upper level trough, a ridge will begin to build
into the region providing warming temperatures and dry conditions
through the middle portion of the week. An area oh high pressure
will build to the south over the Ohio Valley and Southeastern US.
This will allow a southwesterly flow to develop helping to aid in
strong warm air advection resulting in warmer temperatures for the
region. Temperatures will warm to the 60s for Monday and the 70s on
Tuesday. The weather should remain mostly dry through the middle
portion of next week with the influence of this high pressure to
the south of the area.


VFR conditions will gradually deteriorate from southwest to
northeast Wednesday as occasional light rain across western New
York spreads across the remainder of the region and the lower
levels of the atmosphere continue to moisten...resulting in the
development of MVFR to IFR ceilings and eventually some patchy
fog. Expect the worst (IFR) conditions to develop across the
higher terrain...with conditions lowering to MVFR across the
lower elevations.

On Wednesday...widespread MVFR to IFR cigs will be in place across
the region as light to occasionally moderate rain will continue. The
lowest cigs will again be found across the higher terrain.

Wednesday night...MVFR to IFR with lingering showers.
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 through Wednesday...as 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.

In the wake of this system...winds will freshen Wednesday night into
Thursday. This could lead to small craft advisory conditions for
sites on Lake Ontario east of Thirty Mile Point.





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