Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 250521

Area Forecast Discussion
National Weather Service Buffalo NY
121 AM EDT Fri May 25 2018

High pressure moving off the Mid Atlantic coast tonight will
circulate warmer and increasingly more humid air into our region for
the upcoming holiday weekend. This will certainly make it feel like
the first official weekend of apparent temperatures will
climb to levels more typical of July. The summery airmass will
support some scattered thunderstorm activity...which should become
more common as we push deeper into the long weekend.


It will be another beautiful night across western and north central
New York, as a wealth of dry and continued subsidence from an
exiting area of high pressure will offer up mainly clear skies,
with just some passing cirrus. Overnight lows will be comfortable
ranging from around 50 in the coolest Souther Tier valleys and in a
few spots across Lewis county to the upper 50s elsewhere.

Friday promises to be another salubrious day across our forecast
area, as a deamplifying mid level ridge will settle over the Lower
Great Lakes. This will support another day of full sunshine,
although some debris cloudiness will be found over the Thousand
Islands region as a result of some convection near and upstream from
the Ottawa Valley. Mother Nature will tack a couple degrees onto the
H85 temps (16c), and as this airmass becomes fully mixed, we can
anticipate that our afternoon highs will range from within a few
degrees of 80 across the North Country to the mid and upper 80s in
the Genesee Valley and in the warmer Southern Tier valleys.

As we head into the holiday weekend Friday night, a shortwave
digging across the Upper Great Lakes will combine with the offshore
surface high to deepen the south to southwest flow across our
region. This will promote an even milder night with temperatures
forecast to hold above 60 degrees. There may also be a shower or two
across the North Country as a cold frontal boundary will sag south
across the Ottawa Valley.


The sub-tropical ridge will become suppressed off the southeast
coast this weekend and return flow will advect moisture and
warmth into the eastern Great Lakes through Memorial Day. This
will lead to the chance of showers and thunderstorms, mainly in
the afternoon and early evening.

High pressure located well off the east coast will continue to move
eastward Saturday. A cold front will be stretched from west to east
from Lake Superior to northern New England Saturday. A weak pressure
gradient will exist across Western and Central NY as that boundary
stays well to the north. A southwest flow will persist, mainly
across Western NY with lighter winds east of Rochester including the
North Country. Forecast soundings continue to show weak lapse rates
as dewpoints in the upper 50s/low 60s are expected and subtle
subsidence is still present with high pressure off the coast.
Temperatures will rise into the 80s inland and in the upper 70s
along the lake shores. Some interior valleys may see the upper 80s.
As moisture increases through the day, a cu field will likely
develop especially along any lake breeze boundaries. Showers and an
isolated thunderstorm are also possible mainly across the Southern
Tier and interior Western NY/Western Finger Lakes region and along
lake breezes as well as far upstate NY where a boundary persists.

Further upper level trough will approach Ontario Province
Saturday and showers and thunderstorms are expected to develop
across the peninsula Saturday afternoon. The loss of daytime
heating will suppress most of the activity across the Great
Lakes Saturday evening however any stronger showers or storms
will likely move eastward Saturday evening, making their way
across Lake Ontario. Activity is expected to diminish as they
move into an unfavorable environment however can`t rule out an
isolated shower mainly near the Lake Ontario shoreline Saturday

Better conditions exist Sunday for showers and thunderstorms across
the eastern Great Lakes as the upper level trough moves further east
across southern Ontario Province. The frontal boundary to our north
will sag southwestward moving across the North Country and into
Western NY by late Sunday afternoon. A weak gradient flow will also
result in a favorable environment for lake breeze development and a
southwest flow will cause dewpoints to reach the mid 60s by
afternoon. Instability will increase with SBCAPE around 400-800 J/KG
expected by afternoon. The upper level wind field will be weak so
the probability for strong to severe thunderstorms is low. Best
chance for showers and thunderstorms will be Sunday afternoon east
of Lake Erie and then across the region into Sunday evening as
activity that forms across the Ontario Peninsula moves
eastward. Temperatures will reach the 80s Sunday however with
showers and a possible thunderstorm around, temperatures will
likely be a few degrees cooler than Saturday.

The upper level trough will move into northern New England Sunday
night and showers and any thunderstorms will wane into the evening
hours. Upstream activity will also diminish as it moves eastward but
may produce additional showers across the forecast area with
the North Country seeing the longest period of showers into
Sunday night.


A pair of frontal boundaries will quickly track across the forecast
area Monday into Tuesday with a chance of showers and thunderstorms.
The first frontal boundary will move through early Monday and will
provide the focus for shower and thunderstorm most likely south and
east of the both Lakes where the best instability (300-500 J/kg)
will be found across our CWA. Over the course of the day Monday, a
shortwave trough over central Quebec will quickly track east towards
New England into Monday night. As it does so, it will send another
frontal boundary south across the lower lakes, this frontal boundary
at this point looks weak and moisture starved with only a slight
chance of a shower or possibly a thunderstorm as it slips south
through the region. With its passage, any remaining storms will
quickly come to an end with surface high pressure building at
the surface and aloft over New York State. Wednesday, surface
high pressure slips off the Northeast Coast with return
southerly flow picking up and some sub tropical moisture
creeping into our forecast area with increasing chances for
showers and thunderstorms late in the week.

High temperatures will generally range from the U70`s to L80`s
inland away from the lakes for Memorial day (lake temperatures: Erie
51F and Ontario 50F). Tuesday through Thursday, look for highs in
the 70`s near 80F which will continue to be 5F-10F above normal for
late May(normal L70`s for Western and North Central NY).


VFR will prevail through the rest of the night, Friday, and Friday
night as a ridge of high pressure and bubble of dry air remain in
place across the eastern Great Lakes. Expect some passing thin/high
cirrus at times for most areas. The one exception will be the Saint
Lawrence valley, where a slow moving warm frontal boundary and
several weak waves will produce a few periods of showers from late
Friday morning through Friday night. A few scattered thunderstorms
are also possible Friday night. This should all stay north of KART.


Saturday...Mainly VFR. Widely scattered showers and thunderstorms
in the afternoon and evening.
Sunday and Monday...Mainly VFR with scattered showers and


High pressure in the vicinity of the Lower Great Lakes will slowly
push off the Mid Atlantic coast overnight, then will become
anchored well offshore through much of the upcoming holiday
weekend. This will result in light to occasionally moderate
breezes through Friday night with insignificant waves.

As we make our way through Saturday, a weak cool frontal boundary
will sag south across Lake Ontario. This will encourage southwest
winds on Lake Ontario to shift to an easterly component while very
light winds will be found on Lake Erie.

While generally light winds will persist through the remainder of
the holiday weekend, there will be an increasing risk for





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