Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 230540

Area Forecast Discussion
National Weather Service Buffalo NY
140 AM EDT Mon Apr 23 2018

High pressure will slowly drift off the southern New England coast
today and continue to provide sunshine and much warmer temperatures.
Low pressure moving from the Ohio Valley to New England will then
bring occasional rain showers to the region from late Tuesday
through Wednesday. Dry and cooler weather will return by late in the
week as high pressure builds into the Ohio Valley and eastern Great


Clear skies will continue through the rest of the night with
excellent radiational cooling conditions allowing temperatures to
drop back into the 30s in most areas, with some 20s in the cooler
Southern Tier Valleys and east of Lake Ontario.

Surface high pressure will drift off the southern New England coast
today, allowing for more robust boundary layer warm advection to
develop. This will boost 850mb temps to around +5C in the west and
+3C east of Lake Ontario by 18Z Monday. Sunshine and deep mixing
aided by southeasterly downslope flow will boost temperatures into
the lower 70s on the lake plains and warmer valleys this afternoon,
with mid 60s on the higher hills and east of Lake Ontario. It should
be noted that at this time of year, prior to green-up, high
temperatures often over-achieve on sunny, dry days given the lack of
transpiration from actively growing foliage and grass. With this in
mind, went at or above the warmest available guidance.

The southeasterly surface flow will be strong enough to prevent lake
breezes in most areas with a few exceptions. Winds will likely turn
ENE along the south shore of Lake Ontario from near Braddock Bay to
Youngstown this afternoon, keeping the immediate lakeshore cooler.
A lake breeze will also develop in Jefferson County this afternoon,
keeping the lakeshore cooler there. Strong subsidence and dry air
will keep nearly full sunshine in place today, with just some
passing very thin cirrus at times.

Broad southerly warm advection will remain in place tonight. This
will allow for a gradual increase in mid/high clouds from southwest
to northeast overnight. Any showers will remain south and west of
the area through 12Z Tuesday. The southerly breeze will also keep
temperatures milder than recent nights, with lows in the mid to
upper 40s for the lake plains and downslope areas. 30s will be
relegated to a few cool sheltered valleys in the Southern Tier and
Lewis County where surface winds are more likely to decouple.


An upper level trough will slowly move northeastward along the
Ohio River Valley Monday night and Tuesday. A southerly flow
will maintain mild temperatures through this time while moisture
advection increases. Rain showers will begin to move into
Western NY Tuesday. With little upper-level support, showers
should be light going into Tuesday evening.

A fast moving shortwave trough from the western Great Lakes will
phase with the upper level low and low pressure will rapidly deepen
off the Mid-Atlantic coast by Wednesday afternoon. Enhanced synoptic
lift and a strengthening easterly jet will likely produce heavier
rain showers across the eastern Great Lakes Wednesday afternoon into
Wednesday night. Rainfall amounts through Wednesday will range from
three tenths of an inch across the Southern Tier to three quarters
of an inch across portions of the North Country.

Temperatures remain mild through Wednesday night as no airmass
change is expected. Clouds, moisture and a southerly flow
inhibit day time highs some and will keep low temperatures


Periods of showers will continue through Saturday evening before a
break in the weather for late Saturday into the mid-day period on
Sunday. Disagreement still between the models with timing of the
rain for the time between Thursday and Saturday evening.

GFS brings a break in the weather for Thursday morning through
Friday afternoon after the system on Wednesday moves out of the area
and an area of high pressure over the Ohio Valley moves east to the
mid-Atlantic Coast. The ECMWF timing for this break in the
rain/showers comes more during the overnight Thursday through early
Saturday morning period. Both models bring another system similar to
the one that is expected on Wednesday into the region but slightly
more south and west for Friday and Saturday with timing
discrepancies still between the two models.

The GFS has this system a little stronger then the mid-week system.
An area of low pressure over the southeast U.S. will deepen as its
associated upper level trough phases with an approaching upper level
trough diving southeast out of the Ohio Valley toward the southeast
coast. The phasing of the two upper level troughs will help to
strengthen the system as it moves north along the coast and inland
over the Hudson Valley before moving into Quebec and exiting the
region. GFS timing precipitation from Friday afternoon through
Saturday afternoon with some leftover showers/drizzle to follow
through Saturday evening.

The ECMWF has a similar upper level scenario, but doesn`t form as
strong of a coastal low. Instead the ECMWF has a second synoptic
system form over the northern Great Lakes and Quebec, as the two
pieces of upper level energy are a bit to far apart to phase as much
as the GFS solution. A cold front associated with the northern
system will move through the WNY and North Country on Saturday. With
this ECMWF scenario the precipitation would be less than the GFS and
the rain would be much shorter in duration moving through Saturday
morning through the early evening.

Temperatures during this period will cool to below normal with most
areas in the 50s during this four day stretch.


VFR will prevail today and tonight as high pressure drifts slowly
east off the southern New England coast. Just a few thin wisps of
high cirrus will cross the region today, with a gradual increase in
mid and high clouds from southwest to northeast later tonight.


Tuesday...VFR with a chance of afternoon showers.
Tuesday night and Wednesday...Areas of MVFR/IFR with occasional
Thursday...MVFR improving to VFR with a chance of showers.


High pressure will drift slowly east off the southern New England
coast today and tonight. This will continue to provide light winds
in most areas today, although easterly winds will increase locally
at the west end of Lake Ontario this afternoon with choppy
conditions west of Rochester. Otherwise fairly light winds will
continue tonight through the middle of the week as weak low pressure
moves from the Ohio Valley to southern New England.





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