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Area forecast discussion
National Weather Service Buffalo New York
128 am EST Thu Nov 21 2019

Synopsis...
after a few days of uneventful weather...our attention will turn to
a storm system that will track well to our west and north later
today through Friday. This will generate a period of very unsettled
weather across our region...including fairly widespread rain showers
along with some gusty winds. High pressure will then build across
the lower Great Lakes to support fair dry weather for at least the
first half of the weekend.

&&

Near term /through today/...
the axis of a large surface high will push across our region
overnight. While this will assure fair dry weather...low level
moisture trapped beneath a staunch subsidence inversion will lead to
areas of thick stratus. There will also be some fog around...with
the most widespread being found across the higher terrain south of
Buffalo and Rochester. Meanwhile...low temperatures by daybreak will
range from the mid and upper 20s east of Lake Ontario and across the
southern tier to within a couple degrees of freezing across the
lake plains of west of Syracuse.

Thursday, developing low pressure will be sent northeastward by the
southern stream jet from the Central Plains into the central Great
Lakes by late in the day. A strengthening southwest flow within the
warm sector of the system will help temperatures climb into the mid
to upper 40s across much of western New York, with even a few lower
50s possible. Better mixing should help to mix out the expected
lower cloud cover early in the day, for at least some brief partial
sunshine, before upstream cloudiness overspreads the area from the
west during the afternoon. Widespread rainfall developing in advance
of the system cold front should start to makes its way into far
western New York by late afternoon. Wind speeds across far western
New York should steadily increase through the afternoon with some
gusts near 35 mph quite possible in favored downslope areas along
the Lake Erie shoreline from Ripley to Dunkirk.

&&

Short term /tonight through Saturday/...
Lakeshore flood watches were upgraded to warnings and a Wind
Advisory was issued for locations downwind (northeast and east) of
the lakes. This is due to an improved model consensus which supports
a period of strong gusty winds behind a cold front late Thursday
night into Friday.

A pair of mid level shortwaves will cross the central and western
Great Lakes Thursday night and begin to sharpen and phase with time.
The resulting surface low will track from northern lower Michigan
Thursday night to southern Quebec by Friday morning, deepening with
time. There remains some spread in model guidance, but the trend in
18z model guidance and a first glance at the 00z NAM suggests a
trend toward a stronger and further south surface low. Model
consensus shows Post-frontal 925mb winds around 50 knots, and
with Post-frontal mixing typically quite good this will support
wind gusts to 50 mph across the lake plains northeast and east
of the lakes. The 00z NAM remains slightly weaker than other
guidance since it shows an elongated surface low instead of a
compact low which is shown by GFS, rgem, and European model (ecmwf) guidance.
This consensus and the strengthening trend of the NAM provides
ample confidence to upgrade to Lakeshore flood warnings and to
issue wind advisories. If the upward trend in model guidance
continues, warning criteria gusts cannot be ruled out in these
areas.

A strong cold front will sweep east across the eastern Great Lakes
Thursday night, entering western New York shortly after midnight, then
reaching the Eastern Lake Ontario region before daybreak Friday.
Strong winds aloft will last for several hours following the cold
frontal passage. The combination of cold advection, a moderately
strong pressure fall/rise couplet, and a moderately strong
stratospheric pv intrusion will support strong subsidence and
downward mixing of stronger winds from aloft. The strong winds will
be brief, quickly diminishing from west to east Friday as the
surface low moves off into eastern Quebec.

As far as precipitation GOES, a brief Wing of warm advection will
allow showers to develop from west to east Thursday evening. This
will be followed by another brief period of showers along the cold
front overnight Thursday night. Finally, there may be a brief window
of lake enhanced/upslope showers late Thursday night through Friday
morning east of Lake Erie, and during the day Friday east of Lake
Ontario. High pressure and associated dry air quickly build into the
eastern Great Lakes later Friday, so the lake response will be
brief. Precipitation may end as a little wet snow on Friday,
especially across higher terrain. Any snow accumulation will be
minimal.

Temperatures will rise into the mid to upper 40s briefly Thursday
night ahead of the front, then fall back through the 40s and into
the 30s during the day Friday in moderately strong cold advection
behind the front.

Friday night our storm system will be exiting across the Gulf of the
Saint Lawrence, with surface high pressure nudging across the
eastern Great Lakes. The loss of a strong pressure gradient will
result in much less windy conditions, with light winds and perhaps
just a flurry of snow southeast of Lake Ontario on marginal lake
effect snow parameters. Warm air advection will end any flurries
early, though moisture remaining in the lower levels may result in
more clouds than not through the night and into Saturday.

Saturday this surface high will pass by just to our south, with fair
weather conditions through the day. There may even be a period of
mostly sunny skies Saturday before clouds thicken from the south
later in the day as another weak low advances through the Ohio
Valley. The 12z GFS brings this surface low much farther northward
than the majority of its ensemble members...and have tailored the
forecast closer to the NAM/Canadian/ECMWF track which do not bring a
southern stream shortwave as far north as the GFS. Will have
greatest chances for either rain or snow Saturday night and Sunday
across the souther tier, and then The Finger lakes region...with
perhaps near the Niagara River and Saint Lawrence River remaining
dry through the weekend.

This surface low will exit to our east Sunday, with limited lake
effect possible east of Lake Ontario Sunday night. The cold air
behind this weekend storm system will drop to around -7/-
8c...marginal enough for perhaps a light lake response east of the
lakes...especially Lake Ontario.

&&

Long term /Saturday night through Wednesday/...
low pressure passing by to our south and east will exit off the East
Coast Sunday night. There may be some limited lake response
southeast of the lakes, but this will end overnight as a ridge of
high pressure builds into the eastern Great Lakes. By Monday the 12z
GFS shows a weak mid level shortwave crossing the eastern Great
Lakes, while the European model (ecmwf) shows a continuation of ridging surface and
aloft. Favored the European model (ecmwf) for this time period, with a mainly dry
forecast for Monday.

The longwave trough will begin to reload Tuesday across the northern
plains and upper Midwest, allowing a surface low to rotate through
the western Great Lakes and northwest Ontario. Model consensus keeps
most, if not all of the associated precipitation to our west during
this time frame with mainly dry conditions over the eastern Great
Lakes. The longwave trough will begin to move east across the Great
Lakes Tuesday night and Wednesday, although model agreement breaks
down significantly on the handling of the synoptic scale details.
The GFS takes one, strong low through the upper Great Lakes, while
the European model (ecmwf) maintains two separate systems, with a deepening frontal
wave moving across the eastern Great Lakes. Both scenarios would
bring increasing chances of rain by later Tuesday night and
Wednesday.

Temperatures will trend warmer through the first part of next week
ahead of the re-loading trough. A return to at or below normal
temperatures is then likely by the latter half of next week behind
the system noted above, although the degree of cooling shows plenty
of variability in medium range model guidance.

&&

Aviation /07z Thursday through Monday/...
while most of western and central New York will experience VFR
weather for the remainder of the overnight...moisture trapped beneath
a staunch subsidence inversion will encourage areas of strato-cu
that will be based between 2500 and 3500 feet. This will result in
some MVFR cigs at times...mainly across the southern tier.

The lower cigs will lift Thursday morning as a strengthening
southerly flow will help to mix out the low level moisture. This
flow will also advect increased mid level moisture across the state.
This will translate into mainly VFR conditions with surface winds
picking up during the afternoon.

The main issue Thursday night will be related to winds. A deepening
storm system passing over the upper Great Lakes will push a cold
front across our forecast area. A 50kt low level jet will precede
the front...and while the bulk of these winds will remain aloft...
they will support some low level wind shear across the region. In
the wake of the front...winds of up to 40 kts will impact the usual
corridor from Lake Erie and the Niagara Frontier to the Thousand
Islands region. Meanwhile...MVFR cigs will be accompanied by
the likelihood of rain showers.

Outlook...

Friday...MVFR/VFR with a chance of showers. There will be enough
wind to impact ground operations...especially through the midday
hours.
Saturday and Sunday...mainly VFR.
Monday...VFR.

&&

Marine...
a weak pressure gradient will remain in place across the eastern
Great Lakes through Thursday morning, with winds generally 15 knots
or less and waves under 3 feet.

A strengthening area of low pressure will move from the
western/central Great Lakes Thursday afternoon to southern Quebec by
Friday, with a trailing cold front crossing the eastern Great Lakes
Friday morning. Southerly winds will increase ahead of this system
Thursday afternoon and Thursday night, then become southwest on
Friday following the cold front. There will be a period of several
hours Thursday night into Friday when gale force winds will be
possible on both lakes, especially on the eastern end of Lake
Ontario.

&&

Tides/coastal flooding...
another Lakeshore flood event is expected Thursday night
through Friday on both lakes Erie and Ontario. Deepening low
pressure will pass by to the north of the lakes, with several
hours of strong southwest to westerly winds expected behind a
strong cold front.

For Lake Erie, the strongest winds will occur late Thursday
night before quickly diminishing during the day Friday.
Sustained winds will likely reach between 30 and 35 knots for a
few hours on Lake Erie. In periods of normal lake levels these
winds would not be strong enough to produce a warning criteria
seiche on Lake Erie, however all of the Great Lakes are at
abnormally high levels. Given this, levels on Lake Erie are
expected to just exceed the 8 foot level late Thursday night.

For Lake Ontario, the strongest winds will occur Friday morning
before slowly diminishing later in the afternoon and evening.
The combination of High Lake levels, strong onshore winds, and
high wave action will result in Lakeshore flooding and
shoreline erosion on the east half of the lake on Friday.

It should be noted that while flooding may occur, we do not
anticipate impacts as significant as the Halloween night
Lakeshore flood event.

&&

Buf watches/warnings/advisories...
New York...Lakeshore Flood Warning from 4 am to 7 PM EST Friday for
nyz006-007.
Wind Advisory from 4 am to 4 PM EST Friday for nyz006-007.
Lakeshore Flood Warning from 8 am to 7 PM EST Friday for
nyz004-005.
Lakeshore Flood Warning from 11 PM this evening to 10 am EST
Friday for nyz010-019-085.
Wind Advisory from 11 PM this evening to 10 am EST Friday for
nyz001-002-010-011-019-085.
Marine...Gale Warning from 11 PM this evening to 10 am EST Friday for
lez040-041.
Gale Warning from 4 am to 7 PM EST Friday for
loz043>045-063>065.
Gale Warning from 1 am to 1 PM EST Friday for loz042-062.

&&

$$

Synopsis...rsh
near term...apffel/rsh/tma
short term...apffel/Hitchcock/Thomas

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