Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 170244
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
944 PM EST Thu Nov 16 2017

.SYNOPSIS...
Lake effect rain and snow showers east lake Ontario will end
this evening. High pressure will approach the region later
tonight and cross New York Friday with fair weather. A strong
storm system will bring gusty winds and rain late Friday and
Saturday, with colder air bringing lake effect rain and
accumulating snow later in the weekend.

&&

.NEAR TERM /THROUGH FRIDAY/...
Drier air continues to move into WNY and CNY this evening as the
low responsible for the rain earlier today moves further east,
while subsidence from the approaching ridge begins to dominate
the region. Lake effect streamers have ended SE of Lake Erie,
with a similar trend expected for Lake Ontario. Mostly scattered
bands there should around midnight.

What will remain will be trapped low level moisture as seen in
current satellite data. This may take some time to clear without
insolation, but subsidence may help to slowly erode deck with
time late overnight. Many areas along the lake plains may be
clear toward morning, but expect more low level/upslope clouds
still over the terrain. Friday additional clearing should bring
a period of mostly sunny skies before cirrus increases later in
the day from west to east ahead of the next weather system.

Lows tonight will dip into the 20s while highs tomorrow will climb
back into the 30s.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
...Rain transitioning to lake effect snow ...

The ridge axis firmly over the region will shift east Friday night
allowing warm air advection to ramp up. Digging longwave trough
across the western third of the CONUS will become the focus through
this weekend as cyclogenesis gets underway lee of the Rockies,
quickly racing northeastward into the southern Great Lakes by
Saturday morning, reaching very close to western New York by
Saturday evening.

Increasing low level jet late Friday night and through the day
Saturday is expected to yield healthy moisture return with
precipitable water values climbing to near an inch. Isentropic
ascent along attendant northward moving warm front will be more than
sufficient to send a large coverage of rain into western New York
just before sunrise Saturday morning, then expanding over the entire
region through the rest of Saturday morning and continuing through
the afternoon. Rainfall amounts on Saturday are forecast to range
from a half to three quarters of an inch over the Southern Tier and
Finger Lakes region with lesser amounts over the Eastern Lake
Ontario region. Some sites south of Buffalo and Rochester could even
experience higher amounts if the suggested elevated instability
prompts some embedded thunderstorms, which remain in the forecast.
The warm air advection pattern will allow temperatures to climb into
the upper 40s to lower 50s despite the persistent rainfall.

The deepening surface low will track quickly across Lake Ontario
through the Saint Lawrence Valley into Quebec by Sunday. This will
bring a diminishing trend to the precipitation coverage/intensity
Saturday night through Sunday. However, lake processes will
then start to take over as colder air surges into the region
within a quickly developing northwest flow regime. Most of the
precipitation focus for Sunday and Sunday night will be
southeast of the lakes as lake effect rain/snow changes over to
all snow as the cold air deepens along with developing gusty
northwest winds.

The track of the surface low as resolved by the latest 12z NAM and
12z GFS continue to be less favorable for a significant high wind
event for the area. Both models have trended down with their
respective wind fields. Momentum transfer profiles suggesting 35 to
40 knots at best, with the highest wind gust potential confined to
the immediate shorelines of Lake Erie and Lake Ontario.

Over-lake instability certainly looks outstanding with profiles
suggesting moderate to extreme instability developing with lake
induced CAPES over 500 J/KG and inversion heights very respectable.
However, the synoptic moisture fields are far from outstanding with
omega displaced below favorable dendritic growth zone combined with
less than ideal shear profiles all would suggest this lake effect
event will not feature significant accumulations. Yes, plowable
snowfall is likely from the Tug Hill over to Rochester off Lake
Ontario and the Chautauqua ridge and Boston Hills off Lake Erie,
most likely on the order of several inches.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
Lake effect snows will be in the process of diminishing off of both
lakes Monday morning in response to a ridge of high pressure quickly
building in across the lower Great Lakes, which will simultaneously
limit synoptic moisture and lower the capping inversion. As the
ridge builds in, the steering flow will slowly pivot the weakening
snow bands northward across the Tug Hill and south of Buffalo before
ending Monday late afternoon and evening. Temperatures Monday will
remain cool under the subsidence inversion, with highs stuck in the
30s for most locations, with a few 40 degree readings near the lake
shores.

Tuesday, a strong wave will dig into the north central Great Lakes,
encouraging deepening southwesterly flow across the region. This
will usher in slightly more mild temperatures, with daytime highs in
the mid to upper 40s. However, it may not feel too much warmer, as
the stiffening southwesterly winds 20 to 30 mph keep apparent
temperatures in the mid to upper 30s. Cloud cover will also increase
through the day ahead of the wave.

Model solutions diverge into Wednesday and Thanksgiving Day, with
differing opinions on the strength of the aforementioned shortwave,
and the attendant cold front passage. In the GFS/GEM camp, solutions
are more robust, with a stronger cold front, more active frontal
passage with rain/snow showers, and even some lake effect in the
cold air behind the front for Thanksgiving. However, the EC camp
suggests a weaker/more progressive wave with a less interesting
frontal passage and high pressure quickly building in its wake, with
a dry Thanksgiving. Unfortunately that leaves plenty of uncertainty
around the Wednesday travel day and holiday on Thursday, but
confidence is fairly high in a good travel day on Tuesday with mild
temperatures and dry conditions.

&&

.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
There will be an extensive 2500-4000` deck on a WNW flow
overnight, with dry air above this level. Some cloud erosion is
possible over the lake plains later tonight. The WNW winds will
steadily decrease through the night and back to southerly
during the day Fri as surface high pressure moves overhead.

Outlook...

Friday night and Saturday...Rain spreading across the region with
conditions deteriorating to IFR/MVFR and LLWS becoming possible.
Saturday night...Rain changing to snow...and becoming windy.
Sunday and Monday...Lake effect snow and IFR southeast of the
lakes... otherwise mainly VFR.
Tuesday...Mainly VFR.

&&

.MARINE...
Northwest flow will maintain small craft conditions on the Niagara
River and the Eastern Great Lakes tonight. High pressure will
build towards the region later tonight and tomorrow, with SCA
ending later tonight and tomorrow.

After a brief period of calmer conditions Friday afternoon...another
period of strong gusty winds still looks to arrive this weekend as a
stronger storm system tracks northeastward across the Great Lakes.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 4 AM EST Friday for LEZ020-040-041.
         Small Craft Advisory until 4 AM EST Friday for LOZ030.
         Small Craft Advisory until 1 PM EST Friday for LOZ043>045.
         Small Craft Advisory until 10 AM EST Friday for LOZ042.

&&

$$

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



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