Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 260021

Area Forecast Discussion
National Weather Service Buffalo NY
821 PM EDT Wed Apr 25 2018

Low pressure will move northeastward across New England tonight and
into the Canadian Maritimes on Thursday. Lingering showers behind
this system tonight will give way to drier weather from west to east
on Thursday as high pressure and drier air builds across the Lower
Great Lakes. Two more weak systems will then bring additional
periods of rain showers Friday and Saturday.


Tonight a modest shortwave trough along the mid Atlantic coast and a
much stronger shortwave/compact closed low over Southern Ontario
will gradually merge and consolidate across New York State...while
supporting the continued gradual deepening of an attendant surface
low tracking from the mid Atlantic coastline into New England. On
the backside of this system...the combination of a westerly to
northwesterly cyclonic upslope flow of cooler air...increasing
wraparound moisture...and lift attendant to the northern (and
stronger) trough will support relatively high probabilities of
additional rain showers across the bulk of our perhaps
for portions of far southwestern New York where activity should be
much more scattered. Otherwise...moderately breezy conditions will
also develop across the region from west to east as the pressure
gradient tightens between the aforementioned low and high pressure
ridging eastward across the Upper Great Lakes...which should help
to largely scour out any patchy fog that is currently in place.
Meanwhile...modest cool air advection will lead to overnight lows
ranging from the mid to upper 30s across the Southern Tier to the
lower 40s elsewhere.

On Thursday the surface low will exit northeastward across the
Canadian Maritimes as high pressure and much drier air builds
eastward from the Ohio Valley/Upper Great Lakes into western New
York. This will result in any lingering showers diminishing from
west to east through the course of the day...with the activity
hanging on the longest east of Lake Ontario due to the closer
proximity of the low and lingering upslope flow. Following the
departure of the showers...increasing subsidence and drying
should lead to partly to mostly sunny skies developing across areas
south of Lake Ontario during the late morning and afternoon
hours...with some breaks of sun reaching the North Country by late
in the day. Otherwise a lingering pressure gradient will keep
breezy conditions in place...with afternoon highs expected to
mostly range through the 50s.


A weak ridge of high pressure will build into the eastern Great
Lakes on Thursday night with dry weather and clearing skies. Lows
will be in the mid to upper 30s in most locations.

Weak low pressure will track roughly from eastern Virginia to
Southern New England on Friday. There remains some model
disagreement on the exact track, with the GFS a bit further north
and wetter than most other model guidance. There is at least a
chance that showers will clip southern and eastern portions of the
cwa on Friday. Expect highs to be in the upper 50s to lower 60s.

By Friday evening a northern stream trough will approach Western NY
which will result in a chance of showers for the rest of the area.
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.

This trough will usher in colder air and below normal temperatures
for the weekend. Model consensus has 850mb temperatures falling to -
8C as the core of the coldest air moves across the area Saturday
night. This is cold enough for some limited lake enhancement and
also to support snow showers where precipitation still lingers
Saturday night into Sunday. Showers will be light with little if any
accumulation, but this will be perhaps one last taste of winter
before the warm up next week. The forecast hedges below most MOS
based guidance due to high forecast confidence in the cold airmass
and the likely lake enhanced cloud cover during much of the
weekend. Highs will only be in the 40s over the weekend, with
overnight lows near or below freezing on Saturday night.


The anomalously cold upper-level trough will exit the region into the
Canadian Maritimes Sunday night and Monday. Meanwhile, building
500mb heights and an expansive surface high over the Tennessee
Valley will become centered along the Carolinas which will initiate
a strong warning trend across our region. The surface high along the
Carolinas will pump up a much warmer air mass into the Ohio Valley
and Great Lakes which will send high temperatures soaring some +15-
20F degrees above climo by Wednesday with mid-upper 70s, even a
few 80F readings. Late in the week, latest guidance shows a
potent shortwave dropping southeast out of Canada across the
Great lakes while several waves ride northeast along a frontal
boundary to our west. This will likely bring increasing chances
for showers Thursday and Friday. Otherwise, look for relatively
quite weather the first half of the week with dry conditions and
more like summer.


Low pressure over New Jersey will lift northeastward into New
England tonight and then into the Canadian Maritimes on Thursday.
In its wake...high pressure and much drier air will build eastward
into the region on Thursday.

Wraparound moisture behind the low will maintain some lingering
showers and widespread IFR to MVFR ceilings across the region
tonight...with the worst conditions found immediately downwind of
the lakes and also across the higher terrain. While some patchy fog
will also lead to some spotty IFR/MVFR visibilities this evening...
the fog and any attendant reductions should generally tend to
diminish from west to east through the night as surface winds turn
moderately breezy and help to more effectively mix the boundary

On Thursday we can expect improving conditions as the high builds
eastward into our region and brings an end to any showers followed
by a west to east clearing trend...which will result in flight
conditions improving to VFR in most areas by the end of the day. The
one possible exception to this will be the higher terrain east of
Lake Ontario...where some MVFR cigs may linger through sunset.

Thursday night...VFR.
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.


Surface low pressure along the mid Atlantic coastline 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. Light
winds and waves expected through Friday with perhaps waves building
in westerly flow again on Saturday.


MARINE...Small Craft Advisory until 8 PM EDT Thursday for LOZ043.
         Small Craft Advisory until 5 PM EDT Thursday for LOZ042.
         Small Craft Advisory until 11 PM EDT Thursday for LOZ044-



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