Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 281439
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1039 AM EDT Wed Jun 28 2017

.SYNOPSIS...
The upper level trough responsible for the rather cool and unsettled
weather of the past few days will finally move off to our east today...
with high pressure bringing dry weather to the bulk of the region.
Another storm system will then track into our region on Thursday and
provide our next opportunity for showers and thunderstorms...while
also ushering in warmer and somewhat more humid conditions.

&&

.NEAR TERM /THROUGH TONIGHT/...
During the course of today...the axis of the upper level trough that
has plagued our region over the past few days will slide from eastern
New York/western New England to the Canadian Maritimes...while expansive
surface-based ridging over the Ohio Valley builds northeastward across
New York State. For the vast majority of our area...this will translate
into a much-welcomed dry day with just some fair weather cumulus...along
with afternoon highs recovering into the lower to middle 70s as modest
warm air advection aloft pushes 850 mb temps up to between +9C and +12C.

The one exception to the dry weather will be found across the upper
Saint Lawrence Valley and adjoining portions of the North Country...
which will still lie along the western periphery of the departing
trough...and thus under somewhat cooler air aloft. Daytime heating of
this relatively cooler air should yield a decent amount of instability
(MUCAPE of 1000-1500 J/kg) by midday or early this afternoon...which is
precisely when another modest shortwave will be crossing this region in
the prevailing northwesterly flow aloft. In conjunction with lingering
moisture...the instability and shortwave-induced lift should result
in the development of some widely scattered to scattered showers and
thunderstorms...for which some 30-40 PoPs will be in play. With freezing
levels remaining at unseasonably low (7-8 kft) levels...would also not
at all be surprised if a few of these managed to produce some small hail.
Whatever convection that does develop across this particular region should
then quickly wane by late this afternoon/early this evening...as the
shortwave departs and daytime heating diminishes.

Tonight the axis of the surface high will slide east and off the Atlantic
coastline...while low pressure tracks from the upper Mississippi Valley
to Upper Michigan...and eventually pushes its attendant warm front across
far western New York during the overnight hours...with this feature
eventually reaching Lake Ontario by 12z Thursday. After a dry and quiet
evening...the approaching warm front will bring increasing mid and high
clouds to our region overnight...along with the chance of some showers
to the lake plains of western New York. Given that the bulk of the warm
frontal forcing will remain to our northwest with plenty of dry air
remaining in place below 10 kft...at this point precipitation chances
for later on tonight should lie in the lower half of the chance range...
with any rainfall amounts being held to a few hundredths of an inch at
most. Otherwise...it will be a milder night with lows ranging from the
mid 50s across interior portions of the Southern Tier to the upper 50s
and lower 60s elsewhere.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
To start Thursday a warm front will be lifting northward across the
Eastern Great Lakes region...this from a surface low that will be
near the SOO region. The greatest isentropic lift ahead of the warm
front will be across Lake Ontario and points eastward...and will
place likely pops here, while south of Lake Ontario warm air
spreading northward and little forcing will bring a mostly dry start
to the day, with this dry weather lasting a good portion if not all
of Thursday.

Through the day Thursday a southerly flow will bring 850 hPa
temperatures upwards to +15 to +16C. This will promote temperatures
well into the 70s, with lower 80s possible across the downslope
areas of the Genesee Valley. The humidity will also be increasing,
and much greater than what we`ve seen the past few days. Dewpoints
will rise into the mid 60s, and in addition PWATs will rise to 1.75
to 2.00 inches.

Surface winds will also increase Thursday with daytime mixing.
Southwest winds up Lake Erie will reach 25 mph, with gusts 30 to 35
mph from near the shoreline, and across the lake plain to about
Rochester. Winds will not be quite as strong east of Lake Ontario
due to the later arrival of the stronger winds in the lower
levels.

The increasing dewpoints will support SBCAPE values of 1000 to 1500
J/KG. Instability will likely grow largest across the Genesee Valley
and Finger Lakes region if a little sunshine can develop. Aloft a
strong flow of 35 to 45 knots between 925 and 850 hPa will support
thunderstorm development. Though much of the shear Tuesday will be
speed sheer (35 to 45 knots of 0-6 km bulk shear) there will be
increasing amounts of direction shear closer to the warm front
across the North Country. The GFS supercell composite parameter
picks up on the increase in MUCAPE values and shear across the
northern Finger Lakes and Eastern Lake Ontario region...and here is
where strong to severe storms will be possible Thursday late
afternoon and through the evening hours. The southwest winds will
also generate lake breeze boundaries and any boundary cold also
trigger a strong to severe storm across WNY. As a result SPC has our
entire region in a marginal risk for severe storms Thursday and
through the late evening hours. The bulk of the storms Thursday will
be from the very late afternoon hours through the evening as an
upper level shortwave nears.

Thursday night as the weak surface low passes by to our north across
southern Canada, a weak cold front will drop southward across the
region. This will maintain showers and thunderstorms through the
night, with the front dropping southward across the state line late
in the night. There will be little cold air advection behind the
cold front, with much of the cooling restricted to just the lower
few kilometers of the atmosphere. As a result Thursday night will
remain on the mild side with lows in the mid 60s to around 70F, and
with little change in the airmass, dewpoints in the 60s that will
create muggy conditions.

Friday a stronger surface low will track northeastward across the
central Great Lakes. This low will lift the frontal boundary from
Pennsylvania back northward across New York as a warm front Friday.
There will still be a gusty breeze Friday, though likely not quite
as strong as Thursday due to a weaker LLJ aloft. This front will
again trigger another round of showers and thunderstorms. However a
ridge at 500 hPa and the slightly weaker LLJ should limit showers
and thunderstorms, with a good deal of dry time through the day.
High temperatures Friday behind the warm front and ahead of a deeper
surface low will reach into the 80s across much of the region, with
mid 80s across the downslope regions of the Genesee Valley.

Friday night and into Saturday several upper level shortwaves will
round an upper level trough of low pressure. Each of these shortwave
may trigger a shower or thunderstorm, with the greatest coverage
area and intensity likely to be Saturday when a stronger shortwave
passes, and pushes a cold front across the region. We will have one
more muggy night Friday night with overnight lows in the upper 60s
to lower 70s. Saturday ahead of the cold front we`ll have high
temperatures again pushing to around 80, and warmer across the
Genesee Valley and Finger Lakes region. By late Saturday we`ll start
to feel the humidity break, with dewpoints starting to lower.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
Saturday night and Sunday...this time period should mark the end of
an active pattern with high pressure slowly moving in with drying in
at least the mid levels. Humidity levels on Sunday will not be as
great as the last few days of June/beginning of July. The main
threat for additional showers will be on Sunday afternoon along lake
breeze convergent regions.

Sunday night and Monday...this period should be dry with weak high
pressure moving toward the region from the upper midwest. Dry
weather area-wide 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.

Monday night and Tuesday...High pressure generally over head should
negate any threat for convection.  The 12Z GFS is more optimistic
precipitation from the WV/VA Appalachians into PA while the EC is
dry with a slightly stronger ridge over Ontario extending S into NY.
Will lean on the dry side for now as the GFS has had some model
variability further upstream over the midwest when compared to a
more consistent pattern noted in successive EC runs.

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, with a slight cooling trend into early next week.  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 weekend/early next week.  The warmest and most humid
period will be early/during Saturday while in the warm sector.

&&

.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
Mainly dry weather and VFR conditions will be found across western and
north central New York today as expansive surface high pressure ridges
northeastward from the Ohio Valley. The one possible exception to the
dry weather will lie across the Saint Lawrence Valley and adjoining
portions of the North Country this afternoon...where the combination of
daytime heating and the passage of one final disturbance could yield
some widely scattered to scattered afternoon showers and thunderstorms.
This stated...these will likely not impact the KART terminal.

Tonight the axis of the surface high will slide east and off the Atlantic
coastline...while low pressure tracks from the upper Mississippi Valley
to Upper Michigan...and pushes its attendant warm front across far western
New York and eventually to Lake Ontario. While the warm front will bring
an increase in mid and high cloud cover to the region along with the
chance of some showers...VFR conditions should continue to predominate.

Outlook...
Thursday through Sunday...VFR/MVFR with scattered to occasionally
more numerous showers and thunderstorms.

&&

.MARINE...
High pressure building across the Lower Great Lakes will result in
winds and waves remaining below advisory levels through this evening.

As the next frontal system works its way into our region later on
tonight and Thursday...winds will then once again freshen out of the
south and southwest...potentially bringing advisory-worthy conditions
to both Lake Erie and the Upper Niagara River/Buffalo Harbor.

&&

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

&&

$$

SYNOPSIS...JJR
NEAR TERM...JJR
SHORT TERM...THOMAS
LONG TERM...THOMAS/ZAFF
AVIATION...JJR
MARINE...JJR



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