Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 270832
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
432 AM EDT Tue Jun 27 2017

.SYNOPSIS...
Unseasonably cool temperatures with showers and thunderstorms will
continue through today. The upper level disturbances responsible for
the cool and unsettled weather will move east Wednesday with a
return to warmer temperatures by mid-week.

&&

.NEAR TERM /THROUGH TONIGHT/...
A few broken waves of shower and thunderstorms are showing up on
radar at 2am over Lake Erie and adjacent bordering counties. These
are being driven by a sharp shortwave trough over the west end of
the lake and a pool of cold air aloft creating steep low and mid
level lapse rates. Not much going on with mainly clear skies still
in place for much of central NY.

While we continue to forecast lake effect activity consolidating
into a more organized plume this morning as suggested by some
mesoscale models, latest radar trends leave some question to
whether organized lake effect will in fact occur or if we will
just see several waves of convection down Lake Erie and into
western NY. Given the very efficient nature of lake induced pcpn
(esp rain)...rainfall rates in excess of an inch an hour will
be possible. Localized flooding will not be out of the question
if better organized activity develops.

Off Lake Ontario...the airmass will not be quite as unstable and
will have less fetch to work with...so the lake effect rain showers
are not expected to be as organized nor as heavy. Will keep chc pops
in place for much of the Eastern Lake Ontario region...especially
north of the Tug Hill.

Outside of these waves of convection or a more organized development
of lake effect...it will be partly to mostly cloudy and generally
rainfree. Temperatures will bottom out between the low-mid 50s on
the lake plains to the mid and upper 40s across the Southern Tier
and for sites est of the Tug Hill.

After sunrise...the lake effect rain will weaken and dissipate as
the strong late June heating will break apart the lake driven
convection. Nevertheless...scattered showers and thunderstorms can
be expected as the core of the Lake Huron shortwave will pass
directly across our region. H85 temps in the vcnty of 4c will once
again establish very steep low level lapse rates...so any subtle
boundaries will be able to focus convection that could support
torrential downpours and small hail. Temperatures this afternoon
will only make it into the 60s.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/...
Wednesday the axis of the cool upper level trough will now be over
New England. There will remain chances for a few showers east of
Lake Ontario for two reasons. The first is early in the morning,
cool +5 to +6C air will linger over Lake Ontario, and with a
westerly convergent wind a few lake effect rain showers may be
directed towards the Tug Hill region. Any activity will quickly
diminish with daytime mixing. The linger low level lake moisture
combined with the western periphery of the long wave trough may
yield the second reason for showers...this as diurnal activity over
the interior North Country.

Otherwise Wednesday shall be dry as surface high pressure...centered
over the Virginias...passes across the region. Humidity levels will
remain nice, with dewpoints only rising back into the lower 50s.
Wednesday night this surface high will slip to the east. A deep
southerly flow behind this surface high will bring moisture
northward across the Mississippi Valley and up through the Ohio
Valley. To the west of this moisture flux, an upper level shortwave
rippling through a quasi zonal flow will develop a surface low over
the western Great Lakes. The developing nocturnal jet within this
southerly flow Wednesday night will increase isentropic lift, such
that the leading edge of the next rain event may reach the Niagara
Frontier and the Saint Lawrence Valley before daybreak on Thursday.

As a warm front associated with the upstream surface low lifts
northward across the CWA Thursday widespread rain showers will pass
across the region. There will be a fair amount of instability
developing Thursday with SBCAPE values reaching 500 to 1000 J/KG.
With both LI and SI values falling below zero embedded thunderstorms
within the rain associated with the warm front is possible, with
this threat for thunder remaining through the night as the
weakening surface low passes to our north.

The weakening surface low will leave a weak frontal boundary across
the region on Friday. While a shortwave ridge will pass across the
region aloft, the lingering frontal boundary within a moisture rich
atmosphere may allow for a few showers and thunderstorms to blossom
through the afternoon. Expect much of the time Friday to remain dry,
but with much more humidity than recent days as dewpoints increase
into the upper 60s to lower 70s. Showers and thunderstorm chances
will remain Friday night, which will also be quite warm with
overnight lows ranging from the mid 60s to around 70.

&&

.LONG TERM /SATURDAY THROUGH MONDAY/...
On Saturday the next system will move into the Great Lakes region
and will lift a weak frontal boundary back to north, to be followed
by a cold front later in the day. A very moist airmass (PWATS
nearing 2 inches) and dewpoints around 70F supporting SB CAPE values
reaching 1000 to 1500 J/KG will generate showers and thunderstorms
throughout the day.

Saturday night and Sunday...Finally the last shortwave associated
with the long wave trough over the east will bottom out over the
Great Lakes region.  Expect a continued threat for showers, with
some lake shadows east of the lakes for Sunday.

Sunday night and Monday...this period should be dry with weak high
pressure moving overhead. This isn`t a guarantee this far out,
but if the timing of the current pattern holds, the natural
progression should be subsidence behind the Sunday system, with
the exception of isolated summer convection on lake breeze
convergent regions by Monday afternoon.

Daily temperatures won`t stray too far off normals for this time of
year, with highs in the mid 70s to near 80 and lows mostly in the
60s.  Humidity levels will vary, with some nights possibly
warranting A/C while in the warm sector, but at this time don`t see
any extreme sultry days or nights for late into the week/weekend.

&&

.AVIATION /09Z TUESDAY THROUGH SATURDAY/...
Overall VFR conditions are expected to prevail through today but not
without some convection/lake effect to contend with. Several waves
of lake enhanced convection will track across Lake Erie and move
over KBUF/KIAG through the morning. Moderate to heavy rain is
certainly possible within any more organized structured band if it
in fact does develop which could produce TEMPO MVFR conditions at
KBUF/KIAG/KJHW through 12z.

After sunrise...the lake enhanced convection will fall apart during
the initial daylight hours. The attention will then turn to more
scattered showers and thunderstorms as the core of a mid level
disturbance will pass over the region. Again...while short lived
MVFR conditons will be possible with any of the storms...VFR
conditons will prevail.

High pressure will build over the region
tonight with any lingering showers during the evening tapering off
with VFR and some clearing developing.

Outlook...

Wednesday...Mainly VFR.
Thursday through Saturday...VFR/MVFR with a chance of showers
and thunderstorms.

&&

.MARINE...
The main concern for this morning is with a few waves of lake-
enhanced showers and thunderstorms that are tracking across Lake
Erie ahead of an upper level disturbance. These could bring some
gusty winds/small hail and possibly waterspouts.

After sunrise...a persistent southwest graident will once again
support gusty winds as high as 30 knots on Lake Erie. A small craft
advisory remains in place for this body of water...and it is
possible that the BUF Harbor and Upper IAG River will once again
have to be added.

Lighter winds will promote sub-advisory wave action on the lakes
from tonight and Wednesday. Winds and waves will again increase
Thursday ahead of the next frontal system pushing toward the eastern
Great Lakes.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Beach Hazards Statement through this evening for NYZ019-085.
MARINE...Small Craft Advisory until midnight EDT tonight for LEZ040-041.

&&

$$

SYNOPSIS...AR/SMITH
NEAR TERM...RSH/SMITH
SHORT TERM...THOMAS
LONG TERM...THOMAS/ZAFF
AVIATION...RSH/SMITH
MARINE...RSH/SMITH


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