Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 300254
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1054 PM EDT Mon May 29 2017

.SYNOPSIS...
A broad upper level low will meander across the region through much
of this week, bringing periodic opportunities for showers and
thunderstorms along with near to slightly below average temperatures.

&&

.NEAR TERM /THROUGH TUESDAY/...
Upper low centered just north of Lake Superior will broaden with the
addition of upper energy dropping through Central Canada and the
Northern Plains. This system will encompass the Great Lakes through
Tuesday as it slowly wobbles east across Ontario.

Surface low is centered just west of James Bay with a cold front
extending south across Georgian Bay to the western end of Lake Erie
near 11pm. Radar shows scattered and thunderstorms continue to fire
ahead of the front where low level lapse rates remain steep (8.5C/km
00z KBUF RAOB). Storms over the NY western Southern Tier should
dissipate as they shift to the Genesee Valley. Further west more
scattered convection is running along the front. Upper shortwave
pivoting around the low center will swing this cold front east into
our region overnight along with scattered showers and thunderstorms
into western NY progressing east to the Genesee Valley/western
Finger Lakes by daybreak Tuesday. Overnight temperatures will be
mild as a southerly low level flow persists in advance of the front,
which will result in overnight lows mostly in the mid to upper 50s.

The front will continue to push slowly into central NY Tuesday.
Atmosphere will destabilize sufficiently to allow for more robust
convection, especially inland from the lake shadows and well as east
of the Genesee Valley, where instability will likely be maximized.
MUCAPE is forecast to reach 1000-2000 j/kg over the Finger Lakes
ahead of the front with Bulk Shear vectors to 50kts. These
parameters may support a few strong to severe cells with damaging
winds the main threat. SPC Outlook has areas from the Genesee Valley
eastward in a Marginal Risk with the convection Tuesday afternoon,
but remains highly conditional on how much destabilization occurs.
850 mb temperatures in the 8-10 C range will allow most afternoon
readings to climb into the lower 70s.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
Upper level troughing will remain in place across the region
throughout the period, as an expansive upper low remains locked in
place near James Bay. With cool cyclonic flow persisting across the
region, temperatures will remain several degrees below average, with
highs generally in the mid to upper 60s through the period, and
cooler readings northeast of the lakes, including the Buffalo and
Watertown areas, thanks to a persistent brisk southwesterly flow off
of the lakes that will be enhanced by diurnal lake breeze
circulations. Lows during the period will ranges from the low to mid
50s Tuesday night, to the upper 40s to lower 50s Wednesday and
Thursday nights, as the axis of the trough moves over the forecast
area, and cooler air filters across the region.

Regarding precipitation, we will likely see diurnal showers, and
possibly a few thunderstorms winding down Tuesday evening, as a
shortwave crosses the area. Depending on the speed of the shortwave,
we will likely have another round of convection develop Thursday
afternoon, particularly inland from the lakes, away from the
southwesterly lake shadowing. This convection will wind down quickly
Wednesday night, as the wave moves past and NVA associated
subsidence takes hold across the region, with weak ridging and dry
conditions prevailing Thursday. PoPs begin to creep upwards once
again Thursday night, as theta-e advection begins to increase across
the Midwest and lower Great Lakes in advance of a mid-level wave
dropping across the western Great Lakes.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
There will continue to be a deep cyclonic flow across the Eastern
Great Lakes region. There will be some showers and thunderstorms on
Friday, but the weekend is likely to be mostly dry with only a small
chance for showers until the next system arrives Monday.

On Friday, model consensus continues to push a cold front southeast
across the region. This will produce scattered to numerous showers
and thunderstorms, supporting high chance PoPs just ahead of the
boundary.

A stacked low will shift from eastern Canada to the maritimes
Saturday, which will allow an expansive surface high to build across
central Canada. For our region, the forecast question is how far
south will the cold front make it, with the 12Z ECMWF stalling the
boundary across Pennsylvania, which is a bit too close for comfort.
A consensus suggests the boundary will likely settle south of the
area with the ridge extending into Western New York. A shower cannot
completely be ruled out given the close proximity of upper level
trough and the frontal boundary just to the south, but it appears
a mainly dry weekend.

On Monday, a closed upper level low or trough will move across the
Great Lakes region. The 12Z GGEM/ECMWF both favor the slower closed
low solution which would bring a greater chance for showers Monday
than the slightly more progressive GFS. For now, consensus supports
chance PoPs Monday, with the cool and moist pattern likely to
continue well into next week.

Daytime high temperatures will be below normal. Friday will be the
warmest day, with highs in the mid 60s to around 70. After that,
highs should be mainly in the 60s which is about 5-7 degrees below
normal.

&&

.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
Largely VFR conditions expected to continue overnight ahead of a
secondary cold front pushing into the region. SCT SHRA/TSRA activity
over SW Ontario Province/Lake Erie will shift across western NY
overnight. While mainly VFR flight conditions should continue to
predominate, some brief/localized reductions to MVFR cannot be
totally ruled out within any showers or storms. During the day
Tuesday the risk for showers and storms will mainly be east of a
line from KJHW-KROC where some strong to severe storms may form.
Across the west, a southwest lake shadow will keep KBUF/KIAG VFR.

Outlook...

Tuesday night through Saturday...Mainly VFR...with localized MVFR
possible in scattered to numerous showers and thunderstorms at times.

&&

.MARINE...
A secondary cold front will cross the region overnight and Tuesday,
with scattered showers and storms marking its passage. In the wake
of this second boundary, southwest winds will again freshen across
the Lower Lakes region on Tuesday, particularly over Lake Erie where
winds and/or waves could reach lower-end advisory levels.

A broad upper level trough will linger across the region through the
middle and latter portions of the week, resulting in a continued
general southwesterly to westerly flow, with this potentially
pushing advisory levels on Lake Erie on Wednesday.

&&

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

&&

$$

SYNOPSIS...SMITH/TMA
NEAR TERM...SMITH/TMA
SHORT TERM...WOOD
LONG TERM...APFFEL
AVIATION...SMITH/TMA
MARINE...SMITH/TMA


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