Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 261054
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
654 AM EDT Fri May 26 2017

.SYNOPSIS...
While a storm system along the New England coast will continue to
push away from the region today...a wealth of low level moisture
will persist in its wake. This will keep our skies shrouded under
plenty of clouds with a few spots even picking up a light shower or
two. As we head into the long Memorial Day weekend...weak high
pressure will provide most areas with fair weather on Saturday...
but conditions will deteriorate later Sunday into Monday when there
will be the likelihood for showers and thunderstorms.

&&

.NEAR TERM /THROUGH TONIGHT/...
The storm system that was largely responsible for Thursdays soaking
rain is now found along the New England coast. This feature will
push up the coast to Nova Scotia by the end of the day...while a
deep cyclonic flow of very moist air will remain in place back
across our forecast area. Given the light flow and wealth of
moisture below 10k ft...our cloud cover will be quite stubborn and
persistent. This cloud cover will yield some sprinkles and showers
from time to time...with two areas most prone to picking up
measurable showers. The first will be east of Lake Ontario this
morning where an area of showers will rotate back to the northwest
across the eastern Lake Ontario region. Have raised pops to likely
this morning for this area.

Surprisingly...several guidance packages are keying on a subtlety in
the mid and upper levels where channelled/ribbon vorticity will be
generated from an axis of stronger winds ahead of an advancing
shortwave ridge. This kind of feature often enhances lake snows off
Lake Erie...and this afternoon it could act in a similar vein by
supporting a swath of showers that could ROUGHLY line up from the
IAG Frontier to Batavia...Geneseo and southern portions of Ontario
County. There is also support shown by weak low level convergence in
the 10m wind field. Otherwise the bulk of the day should just be
cloudy and largely (but not completely) rain free.

Temperatures today will range from the upper 50s across much of the
Southern Tier and sites east of Lake Ontario...to the mid 60s across
Niagara and Orleans County. These values will be 5 to 10 deg below
typical late May values.

While there may be a couple light showers that persist into the
evening hours...weak high pressure advancing across our forecast
area tonight will provide generally fair weather. Unfortunately...a
light flow will still be in place below 10k ft...and with no fresh
dry airmass in sight...our cloud cover will remain intact. The
mercury tonight will settle into the low to mid 50s across the
western counties...with 40s anticipated across the North Country.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/...
On Saturday weak surface-based ridging will build across our region...
while heights aloft also slowly rise as shortwave ridging pushes east
from the Upper Great Lakes. In advance of this ridge...a modest mid
level shortwave will slide across our region and bring the chance of
a few more showers to the Southern Tier...with drying and subsidence
in its wake then leading to diminishing shower chances and the return
of some partial sunshine to all areas by mid to late afternoon. Under
weak warm air advection...most areas will see highs in the upper 60s
to lower 70s...though it will be cooler along the lakeshores due to
developing lake breeze circulations.

Saturday night the weak surface ridge will slowly drift off into New
England...while its parent mid and upper level ridge crests overhead.
This will promote dry and tranquil weather across our region...with
overnight lows mostly ranging in the lower to mid 50s.

Sunday and Sunday night another large upper level low will dig from
the Canadian Prairies into the Great Lakes...while encouraging its
broad attendant surface reflection to lift from the Ohio Valley to the
Ontario-Quebec border. This will result in the return of much more
unsettled conditions to our region...albeit more slowly than previously
indicated given the continued slowing trend noted in the numerical
guidance suite over the past 24-36 hours. At this juncture it now
appears that Sunday morning may wind up being largely dry...before
the combination of falling heights/warm advection on the front flank
of the encroaching system drive a west-east increase in shower and
thunderstorm coverage Sunday afternoon and evening...with overall
precipitation chances then peaking Sunday night. With continued warm
advection and the slower arrival of the precip...highs on Sunday
should have little trouble reaching the mid to upper 70s in many
areas...with lows Sunday night then settling into the mid to upper
50s.

On Monday the upper level low will advance to a position just south
of James Bay...where it will become vertically stacked over its
surface counterpart...which will swing an occluding frontal boundary
across our region during the course of the day. The best chances for
additional showers and embedded thunderstorms will be found along and
east of this boundary...with precip chances then tending to wane (but
not end altogether) following its passage as somewhat drier air arrives
and large-scale forcing diminishes. Persistent broad troughing and
cyclonic flow will then maintain at least some potential for scattered
showers Monday night...though chances of these will be lower than during
the day with both diurnal instability and organized large-scale lift
removed from the equation. Temperature-wise...highs on Monday should
range in the lower to middle 70s...with lows in the lower to mid 50s
then following for Monday night.

&&

.LONG TERM /TUESDAY THROUGH THURSDAY/...
The large upper level low will only slowly meander its way across the
Great Lakes and southeastern Canada through the middle portions of next
week...with its associated pool of cooler air slowly filtering across
our region. This will result in highs in the upper 60s to lower 70s
Tuesday pulling back into the mid to upper 60s for both Wednesday and
Thursday...while nighttime lows gradually settle back to the upper 40s
and lower 50s.

With respect to precipitation potential...numerous shortwave impulses
rotating around the upper low will result in frequent opportunities
for showers across our region...with some embedded thunderstorms also
possible each day with diurnal heating/destabilization of our slowly
cooling airmass. This said...conditions will also be far from a complete
washout...with periods of drier weather likely found in between the
passing impulses.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
A wealth of low level moisture left in the wake of Thursdays storm
system will translate into widespread IFR cigs over the western
counties this morning...while mainly MVFR cigs will be found east of
Lake Ontario. These cigs will gradually lift to MVFR levels
regionwide for the midday and afternoon when scattered showers will
cover a larger portion of the forecast area.

Tonight...MVFR to IFr cigs will still be in place over the
region...with the lower cigs being concentrated over the Finger
Lakes and Southern Tier.

Outlook...
Saturday...Mainly VFR. Chc of showers early to the west.
Sunday...Mainly MVFR with showers likely. Monday and
Tuesday...MVFR/VFR with a chance of showers.

&&

.MARINE...
In the wake of a departing storm system along the New England
coast...westerly winds will freshen a bit across the Lower Great
Lakes today...but not enough to warrant a new round of SCA`s.

A very weak surface pressure gradient will then be in place during
the passage of weak high pressure tonight and Saturday. This may be
the window of opportunity for recreational boaters this long holiday
weekend...as conditions will deteriorate later Sunday into Monday.

The next storm system will offer an increasing likelihood for showers
and thunderstorms Sunday afternoon and night...with only marginal
improvement anticipated for Memorial Day.

&&

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

&&

$$

SYNOPSIS...RSH
NEAR TERM...RSH
SHORT TERM...JJR
LONG TERM...JJR
AVIATION...RSH
MARINE...RSH



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