Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 262118
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
518 PM EDT Mon Jun 26 2017

.SYNOPSIS...
Unseasonably cool temperatures with showers and thunderstorms
will continue through Tuesday. 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 TUESDAY/...
Feels more like late September/early October this afternoon. Even
some waterspouts were reported on lake Erie early today. Taking a
look at regional radars, showers and thunderstorms have
increased in coverage, especially along lake breeze boundaries
and far inland from both lake Erie and Ontario. Current
mesoanalysis and Amdar soundings shows that 850mb temps have
lowered to around +7C which has steeped lapse rates to 6-7.5C
over the region. This has greatly aided in the development of
showers and thunderstorms this afternoon. Expect these storms to
continue into the evening hours of which some could produce
some small hail and heavy rain.

The feature responsible for this unseasonably cool air is a potent
shortwave trough over the Upper Great Lakes which is expected to
swing across the lower Great Lakes Tuesday. Ahead of this system
southwesterly has kept Erie, Genesee,and Jefferson Counties in our
forecast area largely rain free. This should continue to be the case
into the evening hours as the storms slowly dissipate with the loss
of daytime heating.

Tonight, this anomalously cold core (+4C/+5C at 850mb) within
a deep upper level trough will begin to move into the region.
Rounding the base of this deep upper level trough is a potent
mid level shortwave which will provide the mechanism to push
lake induced equilibrium levels to 25-30K. Expect a fairly
organized lake effect rain event with some embedded thunder
producing locally heavy rainfall off Lake Erie. This lake
effect band under west-southwest flow(240-250)is expected to
hold close to the shoreline and move inland across the Buffalo
Southtowns under this wind flow. Off Lake Ontario, although the
airmass is cold enough Lake Ontario, water temperature is a bit
colder. Instability will not be quite as good and will not be
as supportive as Lake Erie. However, there will still be some
lake response and have some low POPs in this region for
Jefferson county. Temperature wise, look for lows to fall back
into the mid 40s away from the lakes with lower 50s elsewhere.

Tuesday, the deep upper level trough begins to moves east and northeast
of the region with residual showers and possibly a thunderstorm southeast
of both lakes. Expect plenty of diurnal cloud cover with lingering moisture
across the region and cool with highs in the 60s, which will be
10-15F degrees below climo.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
Following the upper shortwave, lingering showers will dissipate
off Lake Erie Tuesday Night while those off Lake Ontario will
persist through the night, albeit weakening towards daybreak.
It will be another cool night with lows generally dropping into
the low 50s and interior valleys down into the upper 40s.

Wednesday will begin to transition to a bit of a warmer pattern as
high pressure moves across the Ohio Valley and a west to
southwest flow develops across the region. Expect fair weather
across much of the region with the exception of the north
country where the lingering cyclonic flow aloft will keep more
clouds and the risk of showers through midday. Temperatures,
while somewhat milder reaching into the low 70s will still be
below normal.

On Thursday the first in a series of surface waves will bring the
likelihood of showers and thunderstorms and the threat of locally
heavy rain. Temperatures continue their slow upward trend with highs
Thursday in the mid to upper 70s.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
A series of systems will affect the region from Thursday night
through at least Saturday and possibly Sunday.  As is often the case
during the summer, rainy periods are not expected to last too long
and there will be several-hour periods of dry weather, but not long
enough to keep any particular day complete dry any part of WNY.
Thus expect at least a chance of showers for each 12 hour
period through Sunday.

Thursday night...The first of a series of systems should move
through on Thursday and drop a frontal system across the region
during or by Thursday night. Thus have a likely chance of showers
and possible thunderstorms in the forecast.

Friday...The frontal system should continue into PA with weak
ridging aloft.  This should mean a lower threat for showers overall,
but still non-zero.  The lowest threat should near/N of Lake Ontario
while areas toward the PA border will have a higher threat for
measurable rain.

Friday night and Saturday...The next system will move into the Great
Lakes region and will drag the frontal band back north (warm front)
across the region.  This will be followed by another frontal system
later on Saturday (cold front).

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 /21Z MONDAY THROUGH SATURDAY/...
VFR is expected at KBUF, KIAG, and KART where lake shadowing
has limited convective development this afternoon. Elsewhere,
expect brief periods of MVFR/IFR conditions in any shower and
thunderstorm activity into the early evening hours. After
sunset, any lingering showers of thunderstorm will slowly
diminish in most locations with a return to VFR.

Tonight, with relatively warm lake temperatures and cold air aloft
look for Lake effect showers to develop and become organized down
wind of both lakes, especially Lake Erie. With a west to
southwest flow in place, lake bands will organized the rain
showers into a single band with potentially some thunder and
graupel near KBUF and maybe even KART along with some MVFR cigs.

Tuesday, expect lake effect showers to diminish with VFR for all
TAF sites.

Outlook...

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

&&

.MARINE...
Have raised small craft advisories for the BUF Harbor and Upper IAG
River...as well as for a small stretch of Lake Ontario from the
mouth of the IAG to Hamlin Beach...as relatively strong winds
stretching northeast from Lake Erie have ONCE AGAIN increased to
small craft advisory levels. Funnelling up the fetch of Lake erie
has been adding 5-10 kts to the gradient wind for the past few
afternoons.

Otherwise...scattered convection along the edges of the Lake Erie
breeze have prompted another round of special marine warnings. The
threat for additional convection driven marine flags will persist
through the evening hours...especially on lake Ontario.

As we work our way through the evening...our very cool airmass will
actually support fairly significant lake effect rain off Lake Erie.
This unusual late June activity will likely contain thunder and
lightning as well...however the convection will yield more heavy
rain than gusty winds.

On Tuesday...a persistent southwest graident will once again support
gusty winds as high as 30 knots on Lake Erie. A long lived small
craft advisory will still be 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 Tuesday night 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 until 11 PM EDT this evening for
     NYZ019.
MARINE...Small Craft Advisory until midnight EDT Tuesday night for
         LEZ040-041.
         Small Craft Advisory until 10 PM EDT Tuesday for LEZ020.
         Small Craft Advisory until 10 PM EDT Tuesday for
         LOZ042.

&&

$$

SYNOPSIS...AR
NEAR TERM...AR
SHORT TERM...LEVAN
LONG TERM...ZAFF
AVIATION...AR
MARINE...RSH



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