Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 280703
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
303 AM EDT Sun May 28 2017

.SYNOPSIS...
Quiet and dry weather will continue to prevail through Sunday morning...
before an approaching low pressure system brings increasing chances
of showers and thunderstorms to western New York Sunday afternoon...
followed by more widespread showers and thunderstorms Sunday night.
After this system exits our region Monday...a large upper level trough
will then meander its way across the region through much of the upcoming
week...bringing a continuation of somewhat unsettled weather along with
near to slightly below average temperatures.

&&

.NEAR TERM /THROUGH TONIGHT/...
Overnight...surface high pressure will gradually shift eastward across
New York State...while maintaining fair dry weather and mainly clear
skies...aside from some lingering stratocu across interior portions of
the Southern Tier/Finger Lakes...and passing thin cirrus across the
rest of the region. With light winds also in place along with narrowing
dewpoint depressions...some patchy fog will also be possible just about
anywhere. Overnight lows will range from the mid and upper 40s across
the Eastern Lake Ontario region and interior portions of the Southern
Tier to the lower 50s elsewhere.

On Sunday surface-based ridging over eastern New York and New England
will slide east and out to sea...with the axis of its parent upper
level ridge also sliding from western New York into New England.
Meanwhile...yet another upper level low will begin digging across the
Upper Great Lakes...with an attendant broad surface low over Illinois
gradually deepening and lifting northeastward to near Detroit. In the
process...this latter feature will push its associated warm front into
southwestern New York this afternoon.

With our area remaining under the influence of the passing upper level
ridge through Sunday morning...we can expect the first half of the day
to be quiet and dry...with a good deal of sunshine early giving way to
increasing diurnal cumulus by midday/early afternoon with strong diurnal
heating of the still-moist lower levels. This stated...it still appears
that any real potential for showers and thunderstorms will hold off until
the warm front approaches/arrives during the mid to late afternoon hours...
resulting in slowly increasing convective potential from about the western
Finger Lakes westward...with the greatest chances for this found over the
western Southern Tier. As for temperatures...the warm advection regime out
ahead of the approaching low will result in 850 mb temps climbing to the
+10C to +14C range Sunday afternoon...which will be enough to support fairly
widespread highs in the mid to upper 70s...with a few of our normally
warmer spots potentially reaching the 80 degree mark. This said...areas
along the Lake Ontario shore from Niagara County over to Rochester will
be kept noticeably cooler by a modest east-northeast flow off the much
cooler lake waters.

As we move into Sunday night...the combination of continued warm air
advection across our region...increasing height falls aloft...and the
aforementioned surface low will provide ample lift in the presence of an
increasingly moist airmass (PWATs climbing to around 1.5 inches)...
resulting in widespread showers developing across our region from west
to east. There will also likely be some embedded thunderstorms as well
given the presence of some weak to modest instability...though the
relatively limited nature of the instability and the unfavorable nocturnal
timing should result in any storms remaining on the tame side. Otherwise
we can expect a rather mild night...with the general warm air advection
regime and a southeasterly to southerly surface flow both helping to
keep temps from falling below the upper 50s to lower 60s...resulting in
overnight lows that will be some 10 to 15 degrees above late May normals.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
The cold front will slice across WNY Monday morning, and
lingering showers and thunderstorms will exit our region through
the morning hours across WNY, and afternoon hours across the
Eastern Lake Ontario region. Dry weather and weak high pressure
will then expand from west to east across WNY and NCNY.

Monday night and Tuesday another upper level low will settle
southward across the Great Lakes region. Several impulses rotating
through this feature will bring chances for showers and perhaps
thunder. The first of these impulses is expected to reach WNY Monday
night, with a chance for showers and thunderstorms before the upper
level impulse dampens out within the mean flow.

Tuesday another impulse, combined with the upper level low drawing
closer will bring increasing chances for showers and thunderstorms.
The bulk of this activity will likely form on lake breeze boundaries
through the afternoon and evening hours. MLCAPE values of 500 to 750
J/KG and PWAT values around three quarters of an inch will provide
the instability and moisture that when interacting with the lift
along lake breeze boundaries, convection is likely to form. A
morning inversion will likely keep this convection at bay, but by
noontime convection should be able to overcome the decreasing
capping inversion. Moisture is not overly impressive, and activity
may be just scattered in nature. Northeast of the lakes, a southwest
stabilizing wind flow will promote sunshine and likely a dry day for
areas such as metro Buffalo, and north of Watertown. Temperatures
Monday and Tuesday will be within a few degrees of normal. Sunday
night, with the late arrival of the cold front, will remain mild
with lows in the low to mid 60s, while behind the cold front Tuesday
night overnight lows will drop back into the 50s.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
An upper level low will remain across southeastern Canada during the
long term period, which will maintain a generally cool and moist
flow during the period. There will still be periods of dry weather,
especially later in the period as the axis of the trough shifts east
across Quebec. However, timing shortwaves embedded in this flow is
difficult, with an increasing spread in model guidance from Thursday
onward.

Temperatures will not change much during the period with highs
in the mid 60s to around 70, which is about 5 degrees below
normal. Lows will range from the mid 40s to lower 50s.

There is good model agreement that a shortwave will cross the region
Wednesday, supporting the best chance for showers and possibly a
thunderstorm during the afternoon hours. After this, the chance for
showers diminishes but cannot completely be ruled out, especially
during the afternoon hours. The 12Z ECMWF/GGEM/GFS have significant
differences in timing, with the only agreement on the general
pattern that changes will diminish on Saturday as the axis of the
trough shifts east. The persistent SW-W flow will result in shadowing
east and northeast of the lakes. In short, while there will be
a persistent chance for showers, the vast majority of the time
should be dry at any given location.

&&

.AVIATION /07Z SUNDAY THROUGH THURSDAY/...
Overnight...expect general VFR conditions to prevail under lingering
high pressure...though the combination of mainly clear skies...light
winds...and narrowing dewpoint depressions could allow for some
patchy IFR/MVFR fog to develop just about anywhere.

Whatever fog that does form overnight will quickly mix out after sunrise
Sunday morning...leaving behind widespread VFR conditions for the balance
of the morning and the early afternoon hours under a developing cumulus
field. An approaching warm front will then bring slowly increasing
chances for showers and thunderstorms to areas from about KROC-KDSV
westward during the mid to late afternoon hours...with some of these
capable of producing brief/localized reductions to MVFR.

Sunday night surface low pressure will move into our region...along
with more widespread showers and embedded thunderstorms. This will
result in areas of MVFR and embedded pockets of IFR...which should
tend to become more widespread late with increasing low level moisture.

Outlook...
Monday...Showers and thunderstorms tapering off from west to east...
with conditions improving back to VFR.
Tuesday through Thursday...Mainly VFR...with localized MVFR possible
in scattered (mainly afternoon) showers and thunderstorms.

&&

.MARINE...
Weak high pressure will gradually shift eastward across New York State
overnight...while maintaining a weak surface pressure gradient that will
keep light winds and negligible waves in place.

As the high slides off to our east and a surface warm front approaches
on Sunday...easterlies will freshen a bit on Lake Ontario...though winds
and waves will remain well below advisory levels. The only ill effects
from this will be choppy conditions on the western end of Lake Ontario
and especially near the mouth of the Niagara River...where the winds will
oppose the outflow from the river. Of greater concern will be an increasing
potential for scattered thunderstorms across during the mid to late afternoon
hours as the warm front pushes into the area...with the threat of these
greatest over Lake Erie.

Showers and thunderstorms will then become widespread over our region
Sunday night surface low pressure slides eastward from the Central
Great Lakes. Meanwhile...winds will continue to freshen while veering
to the south following the passage of the aforementioned warm front.

On Memorial Day...the surface low will swing its trailing cold front
across the region during the morning...with the showers and storms
quickly winding down from west to east following its passage. In the
wake of the front...moderate southwesterlies will also develop...
however winds and waves should remain below small craft advisory
levels.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.

&&

$$

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



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