Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 211954

Area Forecast Discussion
National Weather Service Buffalo NY
354 PM EDT Fri Oct 21 2016

A slow moving low pressure system will move east toward the New
England Coast tonight and then north to northern Maine by
Saturday evening. The widespread rainfall associated with this
feature will move slowly east tonight and Saturday. This will
result in a slow drying trend for far Western New York while
Central New York continues to see additional rainfall through
Saturday. As the low moves east Saturday night, some higher
elevation areas east of Lake Ontario may see a light coating of
snow before the system finally fully moves out of the region.


A slowly deepening surface low over Eastern PA will soon merge
with a coastal low this evening. As this occurs, the low will
continue to deepen but begin to head north in to Northern New
England by Saturday evening. This will result in the far western
sections of the state eventually seeing a slow drying trend, while
the central portion of the state continues to see rain well into
the evening. In fact, expect rain throughout much of Saturday for
areas east of Lake Ontario.

This afternoon, a second baroclinic leaf is forming over Southern
Ontario northwest of the slow moving and gradually deepening surface
low, with an area of deformation aloft from the OH valley north.
Light rain is resulting from this, while the last area of moderate
and occasionally heavy rain appears to be moving north across W
and CNY this afternoon.

This evening...most of the rain within the deformation region
should eventually move south of the region resulting in the
above noted drying trend for far WNY. Some drizzle will be
possible throughout the night however in the exceptionally moist
low level airmass. One problem with this however will be the fact
that an upper level jet has rounded the base of the upper level
trough over the OH valley. This feature is poised to move overhead
this evening and provide additional lift and hence more rain,
albeit with lighter rain rates compared to the past 24-36 hrs. The
result will be the back edge of the eastward moving rain shield
slowing to a crawl overnight somewhere over the Genesee Valley or
Finger Lakes region.

For Saturday...expect little eastward movement of the rain shield
as the low deepens/moves N and the baroclinic zone pivots over
CNY. Pinning down the edge of the rain is not possible...but
highest confidence for continued rain will be East of Lake
Ontario, with little or no rain/drizzle over far WNY.

See the hydrology section below for information for flood/precip


Saturday night a deepening surface low will be found over northern
New England, with the surface forecasted to deepen to sub 980 mb
through the night as it moves to southern Quebec by Sunday morning.
Driving this deep surface low that will approach -4 SD below October
normals will be an upper level trough of low pressure centered over
Southern New England, with PV on the 1.5 level dropping to near 700

The position of this low will result in a northwest flow across our
region Saturday night. Within the trough of low pressure 850 hPa
temperatures will drop to several degrees below zero celsius, and
near -6C over the Tug Hill region. This flow will maintain both
light synoptic as well as lake effect rain showers through the
night. The pool of cold air passing the Tug Hill will likely chance
the rain showers over to snow showers, with perhaps an inch of
accumulation by Sunday morning. Any lake effect activity will most
likely be from Lake Ontario, with a slightly longer fetch than
Erie within the Northwest flow.

The deep surface low will also create a tight pressure gradient
over the Eastern Great Lakes region Saturday night. Combined with
the cold air advection brisk northwest winds will maintain speeds
of 10 to 25 mph through the night, and possibly reach 30 mph along
the Southern Lake Ontario shoreline. Here is where gusts may reach
45 mph or so.

By Sunday the surface low will be advancing farther into eastern
Canada, while beginning to fill...which will relax the pressure
gradient over our region. This will make for a less windy day
Sunday and with slight warm air advection ahead of the next
shortwave we should see a decrease in lake effect showers. There
may still linger a few showers, especially Sunday morning, but
largely we should see some improvements, with some sunshine
possible outside of lake effect bands. The break will be short-lived
as another shortwave dropping across the Great Lakes region reaches
us Sunday night. This will again increase the lake effect response,
with both lake effect as well as orographic lift contributing to
precipitation chances. Will have a chance for precipitation over much
of the region, with highest chances to the SE and E of the Eastern
Great Lakes.

Behind this shortwave, the upper level trough of low pressure that
lingered over eastern Canada will begin to drop southwestward back
to over our region. As moisture increases in the lower levels, and
cooler air aloft returns we should see a redevelopment in
lake effect rain showers to the SE of the Eastern Great Lakes Monday
and into Monday night.

The cool air aloft will bring more typical autumn temperatures this
period. High Sunday may reach into the upper 50s across WNY, but
remain only in the upper 40s to lower 50s across the Eastern Lake
Ontario region which will lie closer to the lingering cool pool
aloft. Monday as the upper level low drops southward, bringing a
cooling atmosphere highs will remain only in the upper 40s to lower
50s which will be a degree or so below late October normal. Lows at
night will range from the low to mid 30s across interior portions
of the Southern Tier and Eastern Lake Ontario region to lower 40s
across the Lake Plains.


We can anticipate a slow moderation in temperature during this a modified Canadian airmass will give way to a Pacific
dominated temperature regime. This negligible warm up will be
accompanied by mainly fair weather through Wednesday...then
conditions will deteriorate as a storm will make its way out of the
nations section. Some day to day details...

A chilly northwest flow found between an exiting storm system over
the Canadian Maritimes and expansive high pressure over central
Canada will encourage some instability over Lakes Erie and Ontario
on Tuesday...but given the general lack of synoptic moisture and
relatively low subsidence cap (inversion)...any lake response will
be meager at best. Will carry slgt chc pops southeast of Lake
Ontario for the time being...while the remainder of the region will
be partly to mostly cloudy. Temperatures will be a few degrees below
normal with afternoon highs in the mid to upper 40s.

High pressure centered over Canada will extend southeast across the
Lower Great Lakes Tuesday night and Wednesday. This will support
fair dry weather with temperatures within a few degrees of normal.
Meanwhile...a Pacific shortwave crossing the Rockies will start the
process of cyclogenesis over the Central Plains.

Our weather will start to deteriorate Wednesday night as a
consolidating area of low pressure will push across the Upper Mid
West. A tightening H925-7 thermal gradient will develop over the
Lower Great Lakes in response of this scenario...with increased
cloud coverage spreading over our forecast area. As the night
matures...there will also be the chance for some rain showers over
the western counties.

On Thursday and Thursday night...the area of low pressure is
forecast to pass by to the west of our forecast area. Deepening
moisture on the warm side of the passing system will be lifted over
the aforementioned baroclinic zone that will be over our area during
the day Thursday...and this will lead to some showers over the
entire region. These showers will persist Thursday night with the
passing of the associated cold front.

While the majority of the forecast area should experience pcpn free
conditions on Friday...will keep chc pops in place to account for
the supporting negatively tilted trough that will be in the process
of pushing out of the area.

Temperatures both Thursday and Friday should top out in the low to
mid 50s.


IFR to low MVFR ceilings will continue into tonight across the
bulk of Western and Central New York as low pressure over eastern
PA moves into the Southern New England coast. The low cloud cover
will be accompanied by widespread rain...which will be heavy at
times east of about KROC-KELZ. The steady rain will combine with
areas of fog to produce IFR to MVFR VSBYS at times. Northwesterly
winds will slowly increase as the surface low tracks into New
England. Rain will become more scattered/broken tonight as
moisture shifts east with the low with some improvement to MVFR
possible for WNY...while rain continues over CNY.


Sunday...MVFR/VFR. A chance for rain showers SE of the lakes.
Monday...Mainly VFR.
Tuesday...Mainly VFR.


An area of low pressure will move from PA to the New England
Coast, then merge with a coastal low and move north to ME. Behind
this surface low a northwest, cool flow will cross the Great
Lakes, slowly strengthening with time. Winds will near or
exceed gale force on Lake Ontario Saturday night.


Some minor flooding is being reported in Allegany County this
afternoon. This was handled with a special weather statement due
to the anticipated ending of the heaviest rain. A flood advisory
was issued for the Irondequoit creek due to continued rises in the
gauged creek. Although there is no flood warning threshold for
this, latest data reports show rises past 8ft, with historical
reports showing minor flooding possible above this level.

Over the next 24 hrs, will have a low QPF over far WNY, near or
under 0.25, but with another inch or so east of Lake Ontario. This
would mean storm totals should end up with a hefty 2-5 inches over
the 2-3 day period, with the highest amounts stretching from the
Southern Tier NE into the Eastern Lake Ontario region.

Despite the impressive amounts, the rain has been steady and
spread out over time. Despite continued rainfall, without a
convective component together with dry antecedent conditions, will
drop the flash flood watch and anticipate only minor flooding from
poor drainage areas.


MARINE...Small Craft Advisory until 8 PM EDT Saturday for LEZ040.
         Small Craft Advisory from 7 PM this evening to 2 AM EDT
         Monday for LEZ041.
         Small Craft Advisory until 8 PM EDT Saturday for
         Gale Watch from Saturday evening through Sunday morning
         for LOZ043-044-062>064.
         Small Craft Advisory until 6 PM EDT Saturday for LOZ043-
         Small Craft Advisory until 11 PM EDT Sunday for LOZ042.
         Small Craft Advisory from 8 PM this evening to 11 PM EDT
         Sunday for LOZ045.



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