Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 271058

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

Unseasonably cool temperatures with showers and isolated
thunderstorms will continue through today. The upper level
disturbances responsible for the cool and unsettled weather will
move east Wednesday with high pressure bringing dry weather. Another
storm system will track into the Great Lakes on Thursday with a warm
front bringing more showers and thunderstorms along with a return to
uncomfortable humidity levels.


The main feature of interest this morning is a sharp mid-level
shortwave trough pivoting across the eastern Great Lakes region.
This continues to drive a several broken waves of showers with
isolated thunderstorms showing up on radar near 7am over much of
western NY and into the Finger Lakes. Still mainly sunny to partly
cloudy skies and dry east of Lake Ontario but the leading wave of
showers should arrive by/near 12z.

Have backed off from previous aggressive forecast for an organized
consolidated band of lake effect showers in favor of synoptic scale
forced convection. There was never and has yet to be any sign of
lake effect organization overnight with current satellite/radar
observations favoring the widespread showers and isolated storms
shifting across western and central New York through today.
Environmental wind shear must have played a part in preventing the
organized lake effect from developing. Outside of these waves of
showers, it will be partly to mostly cloudy and generally rainfree.

In the wake of the shortwave enough lingering cool air aloft will
support more scattered diurnal showers and isolated thunderstorms
through the afternoon. The lake shadow which has kept much of the
Buffalo Metro area shielded from convection in previous days looks
less likely of setting up today due to strong synoptic scale lift so
have broadbrush chance POPs in the wave for the shortwave axis.
850mb temps around +4C will once again support a risk for small
hail. Temperatures this afternoon will only make it into the 60s
with the pool of cold air aloft.

Tonight, subsidence and surface high pressure in the wake of the mid-
level shortwave will bring any lingering diurnal convection to
dissipate during the evening hours with only a chance of some lake
enhanced showers off Lake Ontario tapering off toward Wednesday
morning. It will be another cool night with lows generally dropping
into the low 50s and interior valleys down into the upper 40s.


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.


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.


Overall VFR conditions are expected to prevail through today but not
without some convection to contend with. An swath of widespread
showers with threat for an isolated storm is moving across WNY and
into CNY this morning ahead of a mid-level disturbance. Scattered
showers and isolated thunderstorms will then be the focus this
afternoon as daytime heating works with the core cool air aloft.
While short lived MVFR/IFR conditons will be possible with any heavy
shower or storm, 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


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


The main concern this morning is with a few waves of showers and
isolated thunderstorms that are tracking across the east end of Lake
Erie and north over Lake Ontario ahead of a mid-level disturbance.
These could bring some gusty winds/small hail and possibly

A persistent southwest graident will once again support gusty winds
as high as 25 knots on Lake Erie today. A small craft advisory
remains in place through this evening.

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.


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



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