Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 202231

Area Forecast Discussion
National Weather Service Buffalo NY
631 PM EDT Thu Oct 20 2016

Low pressure tracking by to our south tonight will keep steady rain
in place across western and north central New York. Most areas will
pick up an inch or so of rain by morning...with some sites over the
Southern Tier...Finger Lakes and eastern Lake Ontario region
receiving a much as three inches. The rain will remain in place
through Friday night. Generally unsettled weather can the be
expected for much of the weekend.


At the very least...all of western and north central New York will
continue to receive a soaking rain through at least Friday. There
will also be the risk for moderate to heavy rain though that
could lead to some flooding across parts of the Southern Tier...
Finger Lakes and Eastern Lake Ontario regions. More on this in a

Several ingredients have come into alignment to produce widespread
rain across our region. Starting anomalously strong 150kt
H25 anticyclonically curved jet over Quebec will place our forecast
area region under the jet entrance region. Meanwhile in the low
levels...a stalled frontal boundary draped across Pennsylvania will
continue to serve as a pathway for multiple waves of low pressure to
move northeast. The corresponding baroclinic zone will extend from
Lake Erie and the far western counties to the Thousand Islands this
evening. This thermal gradient will push east during the overnight.
The significant lift provided by the strong upper level jet and the
H925-70 frontogenetic forcing will act upon an airmass that includes
PWAT values of 1.25 to 1.5 inches.

The swath of steady rain associated with this synoptic forcing will
be centered over the far western counties and the IAG peninsula this
evening...but as the next sfc waves moves by to our south
overnight...this swath of rain will push east across the remainder
of our forecast area. Before this eastward shift can take place
though...partial clearing from earlier today allowed a fair amount
of instability to build across Pennsylvania and central portions of
New York. Strong thunderstorms have since developed within this very
unstable and moisture rich environment. This convection will move
northeast across parts of the Southern Tier...Finger Lakes and
Eastern Lake Ontario region this evening...with training cells
offering the risk for significant localized rainfall. This will come
on the heels of roughly an inch of rain that fell over this same
area during the morning and midday. Have thus issued a flash flood
watch for the above outlined area...where upwards of 3 inches of
rain could fall by daybreak.

On Friday...the last in a series of frontal waves will pass by to
our south while the axis of deepest moisture and the effects of the
aforementioned upper level jet will remain in place over our
forecast area. In other words...the basic ingredients for widespread
rain will still be in place. One difference though will be that the
supporting H5 trough just to our west will become negatively
tilted...thus adding some lift from the upper level divergent flow.
Will keep near 100 pops in place with daytime QPF ranging from a
half inch in the far west to between three quarters and an inch east
of Lake Ontario.


Friday night and Saturday the mid level trough will continue to
sharpen and move from the Great Lakes to western New England and
Quebec, closing off into a deep mid level closed low. A secondary
surface low will develop over the Gulf of Maine near the triple
point as the mid level low closes off, with a rapidly deepening low
over Maine or eastern Quebec. Abundant wrap around moisture and
ascent from the slow moving mid level closed low will continue to
support periods of rain showers across the entire region Friday
night, with the most widespread showers found east and southeast of
Lake Ontario by Saturday as the system moves slowly east. Most of
the rain will be light by this time as the stronger forcing and
plume of deep moisture re-organize off the New England coast. That
said, there may be a relatively small embedded area of moderate rain
moving from west to east across the area Friday night and Saturday
in the comma head of the deepening cyclone as a weak TROWAL

Saturday night the system begins to move east down the Saint
Lawrence Valley, with deeper wrap around moisture focusing on the
eastern Lake Ontario region. Precip will remain more widespread
there, while Western NY slowly dries out from west to east as a
drier airmass begins to build into the region.

The airmass will grow cold enough for lake enhancement as lake
induced equilibrium levels rise to around 8k feet. Off Lake Ontario,
this will manifest in the form of some lake enhancement within the
slowly departing comma head of the low. Off Lake Erie, some limited
northwest flow lake effect may develop later Friday night and
Saturday across the Chautauqua Ridge, but short fetch will limit the
coverage and intensity.

Temperatures aloft and in the boundary layer will remain warm enough
for all rain through late Friday night. By Saturday morning the
boundary layer should cool just enough to allow a few wet snowflakes
to mix in across the highest terrain of the Southern Tier and Tug
Hill region. A better chance of a mix and change to wet snow will
come Saturday night east of Lake Ontario, as colder air continues to
wrap around the deepening low. The column should cool enough for a
change to all wet snow overnight across the Tug Hill and western
Adirondacks above about 1200 feet in elevation, where some minor
accumulations are possible. Some wet snow may also mix in across
lower elevations with little or no accumulation.

On Sunday the deep surface low and associated mid level low will
move quickly northeast into the Canadian Maritimes. Any lingering
lake effect and upslope rain/snow showers early Sunday morning east
of Lake Ontario will end, leaving mainly dry conditions areawide
through the rest of the day. A fast moving weak wave of low pressure
over the central Great Lakes will approach later in the day, with
clouds increasing in the warm advection pattern ahead of the low.

Temperatures will bottom out on Saturday, with highs only in the
upper 40s on the lake plains and low to mid 40s across higher
terrain. Expect some recovery by Sunday with highs in the mid to
upper 50s on the lake plains of Western NY, and low to mid 50s
across the higher terrain and east of Lake Ontario.


Sunday night into Monday morning a shortwave trough will cross the
region in the northwesterly flow aloft. This will bring a few
showers across the forecast area, while reinforcing the cooler
Canadian source air into the region. Temperatures will remain near
to slightly below normal for the first half of the work week, as
we remain influenced by the troughing over New England and southern
Quebec. After the departing shortwave on Monday, heights aloft
slowly rise through Wednesday brining a mainly dry stretch of
weather. By Wednesday night into Thursday another shortwave trough
should approach from the Midwest and bring the next chance of


IFR to LIFR CIGS will be found across the bulk of western and north
central New York several waves of low pressure will
push by to our south along a stalled frontal boundary. The low cloud
cover will be accompanied by widespread rain...which will be heavy
at times for sites south and east of a line from ROC to Warsaw to
Jamestown where there could also be some evening thunderstorms. The
steady rain will combine with areas of fog to produce IFR to MVFR
VSBYS. Local delays will be likely.

On Friday...CIGS will generally remain at IFR to LIFR levels with
periods of rain persisting. Again...there will be the chance for

Friday night...MVFR to IFR in occasional rain and fog.
Saturday...Improving conditions far west but remaining IFR to MVFR
from KROC to the Eastern Lake Ontario Region.
Sunday...MVFR/VFR. A chance for rain showers SE of the lakes.
Monday...Mainly VFR. A slight chance for a rain/ North Country snow
Tuesday...Mainly VFR with a slight chance for a shower SE of Lake


An area of low pressure will cross just to the south and east of the
Eastern Great Lakes region tonight. Behind this surface low a
northwest, cool flow will cross the Great Lakes through the end of
the week, and this set-up will bring an extended period of Small
Craft Advisories to the lower Great Lakes.

Through the afternoon and evening will start the period easterly,
and then veer to northerly tonight. Friday, and into Saturday
northwest to west winds will maintain strength in the SCA level,
with winds possibly nearing gale force on Lake Ontario Saturday


NY...Flash Flood Watch through Friday morning for NYZ004>008-013-
MARINE...Small Craft Advisory from 7 PM Friday to 2 AM EDT Monday for
         Small Craft Advisory until 8 PM EDT Saturday for LEZ040.
         Small Craft Advisory until 8 PM EDT Saturday for
         Small Craft Advisory from 2 AM Friday to 2 AM EDT Monday
         for LOZ043.
         Small Craft Advisory until 11 PM EDT Sunday for LOZ042.
         Small Craft Advisory from 8 PM Friday to 11 PM EDT Sunday
         for LOZ045.
         Small Craft Advisory from 11 AM Friday to 2 AM EDT Monday
         for LOZ044.



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