Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 201057

Area Forecast Discussion
National Weather Service Buffalo NY
657 AM EDT Thu Oct 20 2016

Low pressure shifting out of the Ohio Valley will merge with a
dissipating cold front and slowly move across western and central
New York today through Friday. This will bring a near 36 hour period
where several rounds of soaking rainfall will move across our
region. While everyone should pick up at least an inch and a half of
rain through Friday... areas east of a line from Rochester to
Jamestown could pick up three or more inches of rain.


An elongated area of low pressure stretched across the Ohio Valley
this morning is expected to merge with a dissipating cold front over
western Pennsylvania today. This low will become closed off while
shifting just south and east of central New York through tonight.
Aloft, a trough will amplify over the Great Lakes and Midwest
regions in response to a sharp vort max digging into the Tennessee
Valley. Southwest flow within the entrance region of a 120kt upper
level jet along the eastern edge of the trough will draw a plume of
1.25 inch PWAT Gulf of Mexico moisture northeast across our region.
This plume is around 3 standard deviations above normal for this
time of year. Synoptic forcing tied to the trough, jet, surface low
and associated frontogensis will force several rounds of heavy
rainfall over western and especially central NY.

Radar imagery shows a leading swath of rain associated with warm
advection lifting across the western Southern Tier and the Niagara
Frontier. Latest guidance and official forecast calls for the swath
of rainfall to expand and lift north across western and central NY
this morning into the afternoon ahead of a surface warm front
lifting to near the NY/PA border. By about mid afternoon there looks
to be a break in rainfall within the warm sector mainly focused from
the interior western Southern Tier to the southern Finger Lakes. It
is here in the warm sector where a threat of severe storms may exist
with more info on this highlighted below. Meanwhile much of far
western NY north across Lake Ontario and east to north-central NY
should continue to see periods of rain heavy at times as the surface
low approaches with increasing moisture transport and frontogenesis.
and north continue to see rainfall some of which could be heavy.

Concerning the potential for a few severe storms, mesoscale guidance
including recent HRRR runs indicates modest surface-based
instability and strong 0-6km shear of up to 60 kts within the warm
sector may trigger a convective threat where SPC has included a
Marginal Risk for severe storms east of a Jamestown to Dansville
line. There is also a low chance of an isolated tornado should any
supercells spin up along the warm front which should run near the
NY/PA line.

Tonight the surface low is forecast to shift from near Pittsburgh at
00z to about Albany by 12z Friday which is a track just south and
east of our forecast area. A deformation band just north and west of
the low center...or from the Finger Lakes to the North County...will
force the anomalous high moisture plume into a band of heavy rain
overnight. Expect the heaviest rain to fall from about Wellsville
northeast across the Finger Lakes to Syracuse and across the Tug
Hill. Expect a swath of heavy rainfall along this corridor measuring
2-3+ inches where a risk of flooding can not be ruled out despise
the lingering drought conditions. West of this region of heavy rain
from Jamestown to Buffalo to Rochester amounts should run an inch to
an inch and a half through 12 Friday. WPC has included all of our
forecast area in a slight risk for rainfall exceeding flash flood

In terms of temperatures...the extended period of rainfall across
most areas will lead to a narrow diurnal temperature fluctuation.
Highs today should run from the upper 50s from the southern shore of
Lake Ontario to the North Country and low to mid 60s across the
western Southern Tier and Finger Lakes. Tonight temperatures will
likely only slip back into the upper 40s to low 50s.


The rain will continue throughout the day on Friday as the
deformation band responsible for today`s rain continues to slowly
pivot across the forecast area before the main axis of deformation
and lift shifts eastward Friday afternoon into Friday night as the
upper level trough aiding in the rainfall moves overhead. However,
even as the axis of greatest synoptic lift and heaviest rainfall
shifts eastward, showers will persist south and east of the lakes
from Friday night into Saturday as cool, well reasonably well
aligned west-northwest flow develops as the upper level trough moves
through...triggering widespread lake-enhanced showers. A lack of
deep moisture above 850mb will limit precip intensity and coverage
with these showers...particularly as we move through the day
Saturday and the usual diurnal disturbances to lake effect activity
and upper level ridging upstream take their toll. Nonetheless, it
will be a cool and cloudy day Saturday with occasional showers or

We should see a continued decline in shower activity as we move
through Saturday night into Sunday morning, as shortwave ridging
upstream ripples across the area. However, that respite currently
looks to be short-lived as a shortwave trough drops out of the upper
Great Lakes Sunday night, bringing more showers.

Temperature-wise, readings on Friday will run cooler than average as
the frontal boundary slips eastward and cooler air begins to filter
into the forecast area, with highs only topping out in the low to
mid 50s. Temperatures will fall into the mid to upper 30s Friday
night, and a few wet snowflakes cannot be ruled out late Friday
night/Saturday morning across the hilltops of the Southern Tier and
Tug Hill plateau. Saturday will feel downright chilly as the upper
level trough transitions into the forecast area fall into the -2C to
-4C range, yielding highs in the 40s, with lows Saturday night
ranging from the mid 30s to around 40, with the exception of the
cooler North Country where temps may fall to around freezing.

We are currently expecting a slight rebound in readings on Sunday as
the upper level trough shifts east and shortwave ridging moves
overhead...allowing for temperatures to  move back into the low
to mid 50s across the area, with 30s to lower 40s Sunday night.


Temperatures are expected to remain near to slightly below average
as we move into next week as the aforementioned shortwave acts to
reinforce the larger-scale troughing across the Northeast, with
highs generally in the upper 40s to mid 50s throughout the period and
lows Monday night and Tuesday night. The amount of available
moisture, and its subsequent effect on lake effect precipitation is
still in question though, and will hold off on adding in any pops
until Wednesday, when another shortwave moving out of the Midwestern
states impacts the Great Lakes.


Widespread rain associated with a developing warm front ahead of a
surface low will continue expanding and lifting north across western
New York this morning with cigs rapidly deteriorating to MVFR and
IFR by this afternoon. Rain will continue to expand north and east
reaching KART by 18z. Widespread rain with IFR conditions will
continue across all of the region tonight as low pressure passes
just south and east of central New York.

Friday through Saturday...Occasional rain with continued IFR flight
Sunday...MVFR/VFR. A chance for rain showers SE of the lakes.
Monday...Mainly VFR. A slight chance for a rain/ North Country snow


An area of low pressure is advancing across the Ohio Valley this
morning. A strengthening easterly wind through the day today will
develop. This will bring small craft advisory conditions to the
western end of Lake Ontario, and also Lake Erie from roughly Dunkirk
and points southward. A strengthening surface low will then shift
just south of the lakes tonight and Friday, with a cold northwest
flow following over the lakes. This flow will then bring an extended
period of Small Craft Advisory conditions to the eastern Great
Lakes region through the remainder of the weekend.


MARINE...Small Craft Advisory from 8 PM this evening to 8 PM EDT
         Saturday for LEZ040.
         Small Craft Advisory from 4 PM this afternoon to 8 PM
         EDT Saturday for LOZ030-042.
         Small Craft Advisory from 2 AM Friday to 8 PM EDT Saturday
         for LOZ043.
         Small Craft Advisory from 8 PM Friday to 8 PM EDT Saturday
         for LOZ045.
         Small Craft Advisory from 11 AM Friday to 8 PM EDT
         Saturday for LOZ044.



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