Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 260907
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
507 AM EDT Mon Jun 26 2017

.SYNOPSIS...
Temperatures will continue to run cooler than average through
Tuesday, as an upper level trough moves across the region. The
cooler temperatures will be accompanied by showers at times, as a
series of upper level disturbances cross the area. The trough will
move east by Wednesday, with warmer temperatures expected by mid-
week.

&&

.NEAR TERM /THROUGH TONIGHT/...
A chilly airmass continues to spread into the region early this
morning with mesoanalysis showing 850mb temps have lowered to around
+6/+7C over the forecast area. This is certainly cool enough to
promote some lake response over the +22C Lake Erie and +19C Lake
Ontario. As of 4am however only isolated showers are showing up on
area radars with no organized lake effect present. Feel that low/mid
level moisture remains limited well to the west over the Central
Great Lakes near the next shortwave trough. This lack of moisture is
preventing more organized activity from developing this morning but
will keep slight/low chance POPs in place for scattered/isolated
showers.

This next shortwave trough will pivot from over Wisconsin this
morning to over Michigan by this evening. Mesoscale guidance
indicates falling heights and increasing synoptic scale lift ahead
of this shortwave will promote some scattered to numerous showers
and isolated thunderstorms this afternoon mainly inland from the
lakes. Another day with a stiff southwest flow off Lake Erie should
keep the greater Buffalo area dry with showers mainly forming to the
north across Niagara county and east/south into the western Southern
Tier/Genesee Valley and Finger Lakes. A similar shadow effect should
keep Watertown mainly dry as well but winds will be lighter across
Lake Ontario. Cool air aloft will keep a risk for some small
hail/graupel with any stronger/organized showers/storms this
afternoon. Otherwise another cool day is on tap with highs limited
to the mid 60s to lower 70s, more typical of September than late
June.

Tonight the core of our anomalously cool airmass will cross the area
as a potent mid level shortwave moves through the mean longwave
trough. This will help further organize a late June lake effect rain
event as 850mb temps bottom out around +4C. Lake to 850mb deltaTs
will run near 17C which should push equilibrium levels 25-30kft.

Off Lake Erie, mesoscale models are showing potential for an
organized lake effect rain band focusing on the Buffalo southtowns
under west-southwest flow. This will likely hug the Lake Erie
shoreline as well. Given steep low level lapse rates and strong
instability, expect a good chance for some embedded thunder within
the band along with locally heavy rainfall. If the band holds
stationary long enough, rainfall amounts could easily exceed 1 inch.

Off Lake Ontario, The airmass is not quite as cold or supportive of
lake effect rain at the east end of Lake Ontario due to cooler lake
waters. Expecting less of a lake response compared to Lake Erie with
lower POPs included in the grids with only scattered lake effect
rain showers across Jefferson County later tonight.

Outside of the Lake Effect look for partly to mostly cloudy skies
with dry weather. Temps will run below normal with lows expected to
drop to between the lower 50s and upper 40s.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
A September`ish pattern will begin this period as a deep 500 hPa
long wave trough remains over the Great Lakes region. To open
Tuesday a shortwave will be rounding the bottom of the trough,
bringing the coolest 850 hPa temperatures yet with a pool of +4C air
passing over Lake Erie, and later in the morning across Lake
Ontario.

This cool pool of air aloft along with a WSW wind flow ahead of the
shortwave will generate lake effect rain. The shortwave trough
should be upon Lake Erie to start the period and this feature will
begin to veer the boundary winds such that lake effect rain across
the southtowns of Buffalo at daybreak will be pushed southward
towards the So. Tier...where the rain will become more disorganized
within the daytime mixing. Off Lake Ontario a southwest wind will
push lake effect rain towards Watertown and points northward. Lake
instability will not be as great, both with the slightly cooler lake
surface and the later in the morning arrival of the coldest air
aloft. Thus lake effect rain will likely not be as intense off Lake
Ontario as off Lake Erie. Off both lakes, a steady state to the
bands of rain could produce over an inch of rain from late Monday
night and into Tuesday morning...and will continue to mention the
heavy rain possibility. With lake induced equilibrium levels
rising to 25 to 30K feet (mainly over Lake Erie) there will be
chances for thunder within the bands of lake effect rain, with a
waterspout or two possible over Lake Erie.

Otherwise Tuesday will be cool (highs typical of late September)
with scattered showers becoming a bit more widespread in the
afternoon to the east as the upper level shortwave passes. The cold
pool aloft and steep low level lapse rates could trigger a few
thunderstorms that may bear small hail with freezing levels and WBZ
levels low. Skinny CAPE profiles will prevent the small hail from
becoming larger to severe criteria.

Behind the upper level shortwave Tuesday night rain showers will
quickly become fewer in number. Though we will begin to have warm
air advection later Tuesday night behind the eastward shift to the
upper level trough, it will remain cool enough aloft to allow for
some lake effect rain showers across the So. Tier early in the
overnight period Tuesday...and through the night east of Lake
Ontario on a westerly flow. It will be cool Tuesday night with lows
dropping into the low to mid 50s. In areas across the So. Tier and
North Country that can clear out Tuesday night, temperatures will
drop down into the mid to upper 40s.

Wednesday will begin to transition to a bit of a warmer pattern as
850 hPa temperatures rise to around +10 to +12C. This will promote
afternoon temperatures in the low to mid 70s, with increasing
amounts of sunshine. The exception will be across the North Country
where the western periphery of the upper level trough may trigger a
shower through the early afternoon hours. A surface high pressure
will pass to our south Wednesday and light westerly winds will
maintain very comfortable levels of humidity. Wednesday night this
surface high pressure will slip to the east, and a southerly flow
behind the high will begin to bring milder air and moisture
northward. It will still remain comfortable in the humidity
department Wednesday night with dewpoints around 50F...while
overnight lows will not be as chilly as Tuesday night...with
lows generally in the 50s. Near the lake shore the warm lakes
will allow for some shoreline communities to remain in the lower
60s for lows.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
This will be a very unsettled period across our forecast area...as
we can anticipate numerous showers and thunderstorms...including the
likelihood for some localized heavy rain. Temperatures will average
a little above normal...largely due to warm nights...while humidity
levels will climb to uncomfortable levels.

The unsettled conditions will be supported by an oscillating frontal
boundary that will straddle the Lower Great Lakes. Two distinct
surface waves will eject out of a broad...low amplitude trough over
the center of the country during this time period...with each
pushing the boundary back and forth across our region to
force/enhance the convection. The most widespread shower and
thunderstorm activity will be on Thursday in advance of the first
wave...then Friday night and Saturday as the second feature passes.

Max temperatures all four of these days will generally range from
the upper 70s to lower 80s...while overnight lows will mainly be in
the mid 60s.

&&

.AVIATION /09Z MONDAY THROUGH FRIDAY/...
VFR remains in place early this morning with only a few isolated
showers on the radar. A cooler airmass continues to move over the
forecast area where some broken lake effect showers may develop
toward 12z before moving inland as a lake effect modifies to a lake
breeze. Associated convection should become focused inland during
the day as a result of cool air moving overhead. KBUF will likely
see another lake shadow with little to no showers through this
afternoon. Better chances are expected at KIAG/KROC/KJHW. Some MVFR
will be possible with those showers and possibly some isolated
thunderstorms.

Lake effect showers look to become much more organized tonight under
a southwest flow which should direct a decently organized band of
rain showers and potentially some thunder and graupel near KBUF and
maybe even KART.

Outlook...
Tuesday...Mainly VFR with scattered to numerous showers and
thunderstorms...mainly in the afternoons.
Wednesday...Mainly VFR.
Thursday and Friday...VFR/MVFR with a chance of showers and
thunderstorms.

&&

.MARINE...
Although winds have dropped off this morning, expect winds to
quickly pick up again after sunrise today over Lake Erie with
renewed west to southwest winds near 15-25 knots, lasting through
this evening. The pattern looks to again occur on Tuesday with a
little lighter flow but still within small craft advisory criteria.
Waves will generally range from 3 to 6 feet on the eastern end of
Lake Erie with smaller waves on Lake Ontario.

Lake effect rain showers are expected to become well organized
tonight on Lake Erie. This will bring a chance of waterspouts from
tonight into Tuesday morning.

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 from noon EDT today through this
     evening for NYZ019.
MARINE...Small Craft Advisory until midnight EDT Tuesday night for
         LEZ040-041.

&&

$$

SYNOPSIS...TMA
NEAR TERM...SMITH
SHORT TERM...THOMAS
LONG TERM...RSH
AVIATION...SMITH
MARINE...SMITH



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