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Area forecast discussion
National Weather Service Buffalo New York
724 PM EST Mon Nov 18 2019

Synopsis...
a coastal storm may spread a wintry mix into the Eastern Lake
Ontario region tonight through Tuesday morning. Overall though, many
areas will see little if any precipitation through tonight. Chances
for light mixed precipitation will continue off and on into mid
week, then a strong low pressure system will bring windy conditions
along with rain and snow late this week.

&&

Near term /through Tuesday/...
the main wx concern tonight continues to be the chances for
freezing precipitation. Albeit light, only takes a light glaze of
ice to cause untreated surfaces to become slick. The coastal low
will continue to move north off the New England coast and will be
located over Nova Scotia by Tuesday morning. Meanwhile another
potent shortwave in the northern stream trough over the Ohio Valley
will pivot northeast to southern New England overnight causing the
mean longwave trough to take on a negative tilt. This will draw
deeper moisture back toward north central NY, allowing the light
precip shield on the western fringe of the coastal system to get
drawn back to the west toward our Eastern Lake Ontario region. Only
measurable precip tonight will be across eastern portions of the
north country, which again is on the very western fringe of the
precip shield. That said, only have light qpf across Lewis County.
However, ptype will be tricky as the moist layer present is lacking
ice (mainly supercooled water droplets) aloft as temps only get as
cold as -6 to -7c in the moist layer of the column. Putting it all
together looking at the chance for some light freezing drizzle to
move into Lewis County late this evening, transitioning to mix of
light freezing drizzle and light snow showers later tonight as
cooler air works in aloft along with somewhat deeper moisture. With
this in mind, have hoisted a Winter Weather Advisory for Lewis
County for mixed precip from late this evening through late Tuesday
morning. As mentioned above any light glazing of ice can cause
issues. If the western fringe of precip expands just a bit further
to the west, there is the possibility that Jefferson and Oswego
counties may need to be added to the advisory later on. Otherwise,
expecting mainly dry weather across the remainder of the forecast
area through tonight. The exception being the chance for some light
rain showers or drizzle over Niagara and Orleans counties through
the early overnight hours as an area of moisture over southwestern
Ontario pulls off to the northeast. Ground temps here are not
expected not drop below freezing until after any precip ends. Low
temps will range from the mid 20s to around the freezing mark region
wide, with temps remaining above freezing along the Lake Erie and
Southern Lake Ontario shorelines.

Tuesday will start off dry across western New York and The Finger lakes
region, while some light freezing drizzle and light snow showers
continue across Lewis County through late morning before main
shortwave responsible pulls off to the northeast taking moisture and
lift with it, leaving mainly dry weather for the afternoon here.
Somewhat deeper moisture lurking across the Ohio Valley will work
into into areas south of Lake Ontario during the second half of the
day, bringing the chance for some light showers and drizzle by late
afternoon across southwestern New York with temps well above freezing.
Expect areas of light showers and drizzle to expand northeastward
through early evening, with any light rain showers or drizzle
possibly mixing with snow after sunset. Highs on Tuesday will mainly
be in the mid and upper 30s.

&&

Short term /Tuesday night through Thursday night/...
shortwave energy will shear southeast into the base of the residual
mean trough across the Great Lakes and northeast Tuesday night
through Wednesday morning. This will bring another shot of ascent.
Lingering moisture will present another low end opportunity for a
or a mix of light rain or snow, perhaps some freezing drizzle.

Brief reprieve from the unrelenting well below normal temperatures
held within upper troughing starts Wednesday night as upper
ridging builds toward the region. This translates into a
moderating thermal profile. Thursday will be the warmest day of
the total forecast period with temperatures reaching the mid to
upper 40s, perhaps the lower 50s.

This period of warm air advection will be accompanied by deep layer
moisture transport that commences Thursday afternoon, responding to
deepening southwest flow along the downstream flank of a northeast
ejecting southern stream wave. This translates into a period of
widespread rainfall late in the day Thursday and Thursday night.

&&

Long term /Friday through Monday/...
general agreement amongst the various model guidance at the moment
with low pressure tracking northeast through Quebec Canada on
Friday. While this occurs, it will send its trailing cold front
across the lower lakes with a period of rain showers. That said,
strong cold air advection behind the front will rapidly transition
precipitation over to snow for a brief period behind the front late
in the day on Friday. As h850t continue to fall overnight Friday to -
10c/-12c by Saturday morning this will encourage some lake response.
At this point, it appears accumulations will be light and focused
under wnw'erly flow south and east of both lakes. Otherwise, Friday
highs will likely occur early with temperatures falling over the
course of the day with mid to upper 40s early. Behind the front, a
colder airmass will filter in across the region with lows
bottoming out in the 20s by sunrise Saturday.

Well, thats about it for model consistency. Saturday, the GFS pushes
the front well to our east with just chilly conditions and some snow
showers south and east of the lakes. Meanwhile, the European model (ecmwf) features a
low tracking along the frontal boundary out of the Tennessee Valley
towards our region. If this were too occur, it would bring some
light accumulating snow to parts of the region Saturday. At this
point, have kept low end chance pops with all the uncertainty
between the guidance packages. Beyond Saturday, a slow but gradual
warming trend is forecast to begin Sunday with highs climbing to
near normal for this time of year by early next week.

&&

Aviation /01z Tuesday through Saturday/...
mostly VFR cigs can be expected through the first half of tonight,
then lowering cigs to MVFR during the overnight into Tuesday.
The exception will be at kroc where MVFR cigs may be the most
persistent.

During the course of Tuesday...MVFR cigs averaging 2500 ft will
lower to 1500 late...with parts of the southern tier experiencing
IFR cigs.

Outlook...

Wednesday...mainly VFR with a chance of showers.
Thursday...MVFR/VFR with a chance of showers.
Friday...MVFR/VFR with a chance of showers.

&&

Marine...
high pressure over the Canadian Maritimes will result in a
southeasterly flow through this evening directing the highest wave
action and choppiest conditions into Canadian waters. Tonight, winds
will become northeast in wake of a cold front, but winds and waves
will remain below Small Craft Advisory thresholds.

Expect minimal winds and waves through the middle of this week
before both increase late this week as a strong low pressure
system and cold front cross the lower Great Lakes.

&&

Buf watches/warnings/advisories...
New York...Winter Weather Advisory until 10 am EST Tuesday for nyz008.
Marine...none.

&&

$$

Synopsis...jla/SW

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