Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 240404
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1204 AM EDT Mon Apr 24 2017

.SYNOPSIS...
A sprawling area of high pressure across the Great Lakes will
continue to provide for fair weather through Monday evening. A slow
moving area of low pressure moving up the Eastern Seaboard will then
spread showers across our region Monday night into Tuesday. It will
become almost summer like by mid week as the mercury will soar into
the 80s for most areas away from the lakes.

&&

.NEAR TERM /THROUGH TODAY/...
High pressure remains in place across the Great Lakes late this
evening. This is providing for fair weather which will persist
through tonight and Monday. While no rain is expected, some areas of
mid to high level cloudiness are drifting into our region from the
north and south.

A band of mid level clouds just north of Lake Ontario is associated
with a cold front which satellite imagery shows extending from
Northern Maine to southern Quebec and just north of Lake Ontario.
This band of clouds will continue to press south to roughly the
northern shore of Lake Ontario overnight before stalling out as it
presses into our surface ridge. The cloud shield will yield mostly
cloudy skies for the North Country through the late overnight, with
clearing not taking place until Monday afternoon.

Satellite also shows some thin high clouds drifting north across the
NY Southern Tier. These are associated with a leading moisture band
ahead of low pressure centered over the Southeast states. Have
updated the forecast to include these thin clouds which produced
mainly clear wording for the overnight. Have left in some patchy
Southern Tier river valley fog as the thin clouds should still
allow for decent radiational cooling in the Valleys. Northeast winds
will set up Monday as the weak front presses just into PA and a
pressure gradient tightens between low pressure well to our south
and high pressure centered over northern Ontario Province.

Regarding temperatures, with high pressure and light winds should
still promote decent radiational cooling tonight even with the thin
high clouds. Temperatures are expected to easily fall into the upper
30s to low 40s. On Monday, temperatures will feature a north-south
gradient. Readings will run a few degrees warmer across portions of
the Southern Tier, thanks to increasing 850mb temps and
northeasterly flow downsloping into the valleys and to the
lakeshore. On the other hand, areas along the southern shore of Lake
Ontario, north of the NY Thruway will likely run several degrees
cooler, due to this same northeasterly flow enhancing the Lake
Ontario lake breeze and advecting cooler lake-modified air inland.
Thus, expect highs to range from near 70 degrees near the
Pennsylvania border to around 50 near the Lake Ontario shoreline,
with mid-50s to low 60s in the North Country, where the lingering
effects of the cold front will depress temperatures somewhat.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/...
Monday night should start off dry with the region under the
influence of weak ridging. This ridge will start to break down late
in the night when a weak closed low across the mid-Atlantic nudges a
bit closer to the area. A modest 40kt LLJ will increase the 850mb
flow and transport Atlantic moisture into the area. Model consensus
develops showers along this boundary late Monday night. Showers
should become more widespread Tuesday morning, then diminish as the
as the axis of the LLJ lifts north of the area Tuesday afternoon.
These showers should taper off south of Lake Ontario by late
afternoon, while lingering into Tuesday evening east of Lake
Ontario. Despite likely PoPs in many areas, showers only last a
couple hours so Tuesday will be far from a washout.

Temperatures will be seasonably cool Monday night, with lows mainly
in the lower to mid 40s. Highs Tuesday will generally be in the
upper 50s to lower 60s, with mid 60s across the lake plains west of
Buffalo where downsloping and a partial clearing will help warm
things a bit.

The region will be in between the weakening coastal low and an
approaching trough late Tuesday night through Wednesday night. This
will keep Western New York dry, with mid-level riding supporting
a clearing trend Wednesday afternoon and night.

Despite some differences in guidance, there is little doubt that
temperatures will be above normal Wednesday. Expect highs in the
70s, with a weak southeast flow and associated downsloping bringing
the warmest temperatures to the lake plains. This also will help
limit the inland extent of the lake breeze and keep cooler
afternoon temperatures very close to the lakeshores. Given model
differences the forecast sticks close to model consensus, but does
enhance downslope influences where are likely to be missed by lower
resolution guidance.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
Thursday will likely have a summer feel to the day as a narrow 500
hPa ridge extends northward, between a cut-off low off the SE New
England coastline, and digging trough across the Midwest. Much of
Thursday will be dry, but as this upstream trough, with moisture
pooling ahead of a cold front nears, showers and thunderstorms will
start to blossom through the afternoon and evening hours. Activity
at first will likely be along lake breeze boundaries across WNY,
then as the cold front crosses Thursday night, there will be chances
for storms everywhere. A southerly wind will bring 850 hPa
temperatures spiking towards +15 to +18C across the region and this
should bring a very warm day to the region, with most areas reaching
into the 80s.

It will then turn cooler, and less humid later Thursday night and
into Friday behind the cold front. Some lingering moisture towards
the SE region of the forecast area may allow for an afternoon
showers or thunderstorm, but the bulk of Friday appears to be dry.

Another storm system, with a warm frontal boundary nearing the
region next weekend will bring the next threat of rain. There will
be chances for showers and thunderstorms both days with the frontal
boundary nearby. Temperatures both weekend days will likely average
above seasonal normals.

&&

.AVIATION /04Z MONDAY THROUGH FRIDAY/...
Widespread VFR conditions will continue through Monday, thanks to
high pressure over the Great Lakes. A cold front shifting south out
of Canada will cross Lake Ontario, spreading mainly mid level clouds
across the North Country tonight, but cigs should remain VFR.

Thin clouds have also spread north into the western Southern Tier
well ahead of low pressure over the Carolinas. These high cigs will
maintain VFR. Northeast winds will set up Monday as a pressure
gradient tightens some between the low pressure center well to our
south and high pressure center over northern Ontario Province. Some
guidance such as the NAM DMO show possible IFR along the southern
shore of Lake Ontario for KIAG and KROC with northeast winds off the
lake for a brief period centered around 12z but confidence is low in
this outlier guidance so have left out of the TAF. Otherwise,
VFR through Monday.

Outlook...

Monday Night...Mainly VFR with a chance of showers.
Tuesday...Mainly VFR with showers likely.
Wednesday...VFR.
Thursday...VFR/MVFR with a chance of showers and thunderstorms.
Friday...Mainly VFR with a slight chance of showers and
thunderstorms.

&&

.MARINE...
Northeast winds will freshen later tonight on Lake Ontario resulting
in Small Craft Advisories along the south shore for Monday. This
increase in winds and waves is due to a tightening pressure gradient
between a slow moving surface low moving up the East Coast and high
pressure centered over northern Ontario Province. Winds and waves on
Lake Erie are not expected to reach advisory levels as the winds are
parallel with the southern lake shore.

Winds will veer to the east Tuesday, as a ridge across the region
becomes re-oriented, shunting most of the wave action to Canadian
waters. By mid-week, conditions on the lakes will become more
tranquil as the pressure gradient relaxes.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory from 5 AM early this morning to 8 PM EDT
         this evening for LOZ042>044.

&&

$$

SYNOPSIS...RSH
NEAR TERM...SMITH/WOOD
SHORT TERM...APFFEL
LONG TERM...THOMAS
AVIATION...SMITH/WOOD
MARINE...SMITH/WOOD


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