Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 290227
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1027 PM EDT Wed Jun 28 2017

.SYNOPSIS...
A warm front will move into the region late tonight, bringing
light showers. Then some showers and thunderstorms will develop
late Thursday, and some could produce gusty to damaging winds.
Unsettled, warmer and humid weather will continue through the
weekend before high pressure builds in early next week bringing
seasonable and drier weather.

&&

.NEAR TERM /THROUGH THURSDAY/...

A warm front extends southeastward from low pressure centered
across northwestern Wisconsin late this evening. A sharp mid-
level thermal gradient is north of the surface front, and this
is forecast to lift across the region overnight. Radar shows
some light showers along this boundary which should become more
widespread as remnants from convection across northern Illinois
streams along the mid-level boundary. This is supported by model
consensus, which also shows precipitation becoming more
widespread. Initially, this probably will bring sprinkles or
light showers to the Niagara Frontier which will struggle to
reach a few hundredths of an inch. As more moisture feeds in,
there is increasing confidence there will be measurable
precipitation across the North Country later tonight. Overnight
low temperatures will be mainly in the 50s, except across the
lake plains where downsloping may keep temperatures from falling
below 60.

By Thursday morning the frontal boundary will be in place across the
North Country, with locations south of Lake Ontario established into
the warm sector. A shortwave will ride along this boundary, helping
to force a more widespread area of rain for the North Country. This
will also organize an area of scattered showers with perhaps a few
rumbles of thunder that will move across locations south of Lake
Ontario during the morning hours. In the wake of this shortwave, we
should see perhaps some sunshine breaking through to help
destabilize the warmer, humid airmass advecting into the region.

There is a considerably spread in guidance stemming from the
specific timing and location of this shortwave which depends on
upstream convective development. Depending on how unstable this
airmass can get, we should see some thunderstorms develop off
the combination lake breeze / pre- frontal trough by late
Thursday afternoon. The wind field will be fairly fast and
unidirectionally increasing with height in the warm sector. This
will support a marginal threat for severe weather, mainly in
the form of isolated damaging wind gusts.

However, this will be a scenario where Buffalo/Niagara Falls and
Watertown likely remain mostly dry if not sunny at times through
Thursday afternoon. This will be due to the robust, synoptically
aided southwesterly flow lake breeze that will develop. A core of
40+ knot winds will develop near 2kft, which will funnel up Lake
Erie. The warm advective pattern, with poor low-level lapse rates
across the Niagara Frontier will help keep all of that wind from
mixing down. However, can easily see gusts topping out around 35
knots, or 40 mph. Would not rule out a couple gusts around 45 mph,
especially at Niagara Falls, with the mainly 220 wind direction that
can tend to have an isentropic downslope effect off of the cooler
Lake Erie.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
Thursday night will mark the beginning of a warm and humid period
with multiple opportunities for showers and thunderstorms lasting
through Saturday.  A warm front will already be north of the region
by Thursday night, while a weak cold front tries to move toward the
region. But while some weak troughs may move through Thursday night
or Friday, it`s looking less likely that the main boundary will make
much headway into WNY.  This appears to be due to the fact that the
slow moving upper level flow will spawn either a few surface lows
moving NE into the upper Great Lakes region or result in just one
low generally S of James Bay with a persistent trailing NE-SW trough
co-located with an upper level jet stuck over an area between about
Missouri to Quebec. As a result, the region will likely end up
in the warm sector for the majority of the time until the cold
front finally wafts through late Saturday or Saturday eve.

The result will be low confidence on timing precipitation events
from Thursday Night through Saturday.   That said, it`s safe to say
that mesoscale boundaries will play some role in focusing
convection, with a high chance for ongoing convection inland of WNY
into the Eastern Lake Ontario region Thursday evening, with a lower
threat in lake shadowed regions along the lakeshores.  As lake
boundaries lose their influence, upstream convection may be able to
move across the lakes later Thursday night and Friday AM.  A repeat
idea is plausible on Friday, with lake breeze/convergent boundaries
driving higher convective chances toward Friday afternoon and
evening.

Finally on Saturday, the upstream frontal boundary should start
making some headway and either move through during the afternoon or
evening hours Saturday evening.  This will result another chance for
afternoon convection, particularly on lake breezes.

With warm and humid air in place for this period, expect
temperatures climb toward the low 80s in most spots but with
humidity levels being a little uncomfortable at times.  The sultry
period may be Friday Night through Saturday with dewpoints in
the upper 60s and/or near 70.

In terms of severe weather, there doesn`t appear to be too much of a
signal for widespread severe.  With the warm and moist airmass,
large hail is unlikely.  There might be a wind threat on Friday
inland along and east of lake breeze with higher shear, but this may
be isolated.  Possibly a slightly greater threat may be heavy rain,
particularly in the eve/overnight hours Friday night and/or Sat with
a stronger low level jet near about 30kts together with high PW
between about 1.75-2.00".

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Cooler and drier air will start moving into the region on Sunday.
This won`t make much of an impact at the surface in terms of daytime
temperatures, but with dewpoints dropping through the 60s, humidity
levels should be more comfortable for the remainder of the weekend
into next week.  There will still be a chance for convection on
Sunday on lake breezes, but most areas outside of these localized
areas should remain dry.

By Monday, a ridge should be moving eastward through Ontario and
into Quebec, and extending S through NYS.  This should result in a
dry period, including Monday eve for any early fireworks displays.

For the Fourth of July, there are some model discrepancies with the
EC bringing a surface trough and related precipitation in the
region.  Looking higher up, there isn`t anything that fits this
scenario - no identifiable shortwave troughs.  The GFS on the other
hand has convection breaking out over Southern Ontario and into
Western NY/Central PA indicative of scattered afternoon/eve
convection on lake breeze boundaries.  Thus will have a low chance
of afternoon/eve convection, mainly inland.  But this is ~7 days out
and much can change.

&&

.AVIATION /02Z THURSDAY THROUGH MONDAY/...
VFR conditions will prevail overnight. Clouds will increase
from west to east overnight ahead of the next approaching
weather system, with some light showers possible from this mid-
level cloud deck. Light rain showers will become a bit more
widespread across the North Country (including ART) but the
flight category will likely remain VFR Thursday morning. As
rain showers persist near the boundary MVFR conditions are
possible at ART Thursday afternoon.

Scattered thunderstorms are possible Thursday afternoon, but
there will be a strong SSW flow which will lower the chance for
storms to develop at BUF/IAG/ROC. Expect mainly VFR conditions
with locally lower conditions in thunderstorms.

Outlook...
Thursday night...VFR/MVFR with showers likely and possibly a
thunderstorm. LLWS possible.
Friday through Sunday...VFR/MVFR with scattered to occasionally
more numerous showers and thunderstorms.
Monday... Mainly VFR.

&&

.MARINE...
High pressure building across the Lower Great Lakes will result in
winds and waves remaining below advisory levels tonight. A warm
front will enter the region late tonight and lift northward
across Lake Ontario Thursday. Winds will increase, especially on
Lake Erie with a SSW flow. This is not ideal to build waves, but
should be ample to just hit the 5 ft threshold, with gusty winds
also on the Niagara River. Winds and waves will diminish
Thursday evening.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Beach Hazards Statement from 9 AM EDT Thursday through
     Thursday evening for NYZ010-085.
MARINE...Small Craft Advisory from 9 AM to 8 PM EDT Thursday for LEZ020-
         040-041.
         Small Craft Advisory from 9 AM to 8 PM EDT Thursday
         for LOZ030.

&&

$$

SYNOPSIS...APFFEL/CHURCH
NEAR TERM...APFFEL/CHURCH
SHORT TERM...ZAFF
LONG TERM...ZAFF
AVIATION...APFFEL
MARINE...APFFEL/CHURCH


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