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Area forecast discussion
National Weather Service Buffalo New York
718 PM EST Thu Nov 21 2019

Synopsis...
a storm system will track well to our west and north tonight and
Friday. This system will generate a period of very unsettled weather
across our region, including the likelihood for 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
day of the weekend.

&&

Near term /through Friday night/...
low pressure will strengthen to around 992 mb as it tracks from
Lake Huron this evening and into western Quebec later tonight. This
system and associated cold front will bring gusty winds and
widespread precipitation to western and north central New York
with tonight.

The main concern is the winds. Forecast soundings still showing
a variety of boundary layer profiles. Rain may limit mixing
level heights ahead of the cold front, however the Chautauqua
ridge may provide funneling across the lake plains which could
result in prefrontal wind gusts near Lake Erie. The best gust
potential will be within the cold air advection behind the
system cold front, resulting in a more widespread strong winds
due to effective downward momentum transport.

The strongest winds will only last 3-6 hours, starting around
11 p.M. At Buffalo, 2 a.M. At Rochester, and 4 a.M. At
Watertown. The strongest winds will be from Lake Erie, across
the Niagara Frontier over to Rochester to the Thousand Islands
region. Gusts to 50 mph can be expected in these areas.

This rainfall will be mainly supported by strong isentropic lift as
the surface low strengthens during its track north and west or the
area. Good moisture will accompany this system as a strong low level
jet of 50-60 knots Ushers in a moist airmass. This will help
precipitable water values increase to near an inch this
evening. Though probabilities for rain are fairly high,
rainfall amounts should be a third of an inch or less with the
highest amounts focused across the Eastern Lake Ontario region.

Precipitation is expected to push east of the area Friday
morning, but as colder air arrives, a transition over to wet
snow is possible, especially over the higher terrain east of the
lakes as some lake contributions starts to evolve. Any
accumulations should be minor and under a half inch or so. Cold
air advection should limit any temperature gain during the day
Friday, we are more likely to see temperatures fall back a bit
to near freezing by the end of the day.

Large scale subsidence through the mid-levels officially shuts down
precipitation chances along with building surface high pressure
which will dry US out through Friday night.

&&

Short term /Saturday through Sunday night/...
Saturday surface high pressure will drift east across the mid
Atlantic states, with a weak ridge extending up into the eastern
Great Lakes. This will bring a return to dry weather and lighter
winds. There will be at least some clouds around, initially from
lingering lake effect clouds and then increasing mid/high clouds in
warm advection later in the day. The quick push of colder air Friday
and Friday night will exit during the day, with warm advection
supporting highs in the low to mid 40s in most areas with the
exception of Lewis County.

Saturday night and Sunday model guidance diverges significantly.
There is still a very wide spread in the guidance envelope for the
handling of the track of the next system, especially considering it
is only a few days away. The vast differences arise from the degree
of phasing between the southern and northern stream, or lack
thereof. The GFS is most aggressive with phasing a southern stream
shortwave moving through the Ohio Valley and a digging northern
stream shortwave moving into the western Great Lakes, which would
support a more well developed and much farther northwest low track
Saturday night and Sunday morning. The NAM is on the other extreme,
taking a faster and suppressed low offshore of the mid Atlantic
Saturday night with no phasing at all. The Canadian Gem is very
similar to the GFS, while the European model (ecmwf) plays The Middle Ground with
some phasing and a low track between the GFS and NAM solutions.

Given the high degree of spread between the various models and
ensemble members, continued to offer chance probability of precipitation spreading northeast
across the area Saturday night and continuing through the first half
of Sunday, with relative higher chances across the southeast and
eastern portion of the area. If precipitation does materialize,
there will likely be a mix of rain and wet snow given the marginal
temperature profiles. The low levels will initially be nearly
isothermal and near the freezing mark Saturday night, with cold
advection aloft then steepening lapse rates by Sunday morning. The
setup looks to generally favor rain or wet snow, with little
opportunity for sleet or freezing rain given the lack of a warm
layer aloft. If the farther northwest and stronger GFS/Gem solutions
verify, there may be some minor accumulations of wet snow late
Saturday night and Sunday morning.

The chances for synoptic precipitation will taper off from west to
east Sunday. The airmass behind this system will grow just cold
enough to support some lake response Sunday and Sunday night east of
the lakes. The boundary layer wind direction and thus placement of
lake effect will ultimately depend on the eventual track of the low,
but it generally looks to be west or west-northwest. This may allow
for some minor accumulations across the higher terrain east of the
lakes, but instability and surface temperatures appears too marginal
for anything other than light accumulations.

&&

Long term /Monday through Thursday/...
Monday the longwave trough will begin to re-Load over the northern
plains, allowing for downstream height rises and warm advection
across the Ohio Valley and eastern Great Lakes. This will provide
dry weather and temperatures at or slightly above average. The
northern plains trough will make some headway moving east into the
Great Lakes by Tuesday, but the stronger forcing will still remain
west of our area. The approach of forcing and moisture may support a
chance of a few showers by Tuesday night, with most of Tuesday
remaining dry. The early week warm-up will likely peak on Tuesday
ahead of this trough, with highs in the lower 50s across the lake
plains.

Model guidance begins to diverge again with the handling of synoptic
scale details past Tuesday. In a general sense, the deepening trough
will move east across the Great Lakes and New England during the mid
to late part of next week. This will bring a return to near or below
normal temperatures later next week. How the cold air arrives is in
question, with a variety of model solutions in the handling of
potential significant cyclogenesis across the Great Lakes. The GFS
is again most phased with the northern and southern streams, taking
a strong low through the central Great Lakes Tuesday night and
Wednesday. Past runs of the European model (ecmwf) had less phasing and a more
suppressed system going over or just southeast of the area. The new
12z European model (ecmwf) has trended back to the GFS, with a strong low passing
just north of lakes Erie and Ontario. The 12z GFS and European model (ecmwf)
solutions would suggest the potential for a damaging wind event
across the eastern Great Lakes. That said, given the model variation
we have seen, confidence is low in this scenario for now. Model
trends will need to be closely monitored in the coming days.

Following this potential significant system, a west to northwest
flow of colder air may support some lake effect snow potential east
and southeast of the lakes later Wednesday through Thanksgiving day,
although details with placement and amounts are always highly
uncertain almost a week out.

&&

Aviation /00z Friday through Tuesday/...
a 50-55 low level jet will move across the region this evening.
Winds will be south-southwest with the strongest winds remaining aloft
resulting in a period of low level wind shear. Mixing will improve with the
approach and passage of a cold front which will move through buf
around 05z and Art around 09z. Confidence in timing is good (+/-
an hour). Expect wind gusts to 40 kts near and just behind the
front.

There will also be rain showers will the low level jet ahead of the front
this evening, but these will be modest in intensity with mainly
VFR conditions for the start of the 00z taf cycle. Low moisture
will increase with the arrival of the front, with a period of
MVFR to IFR flight conditions due to lower cigs along and just
behind the frontal passage.

Conditions will gradually improve during the day Friday as
drier low air moves into the region. Ceilings will lift and
begin to scatter Friday afternoon giving way to mainly VFR
conditions. There will be some lingering lake and upslope
enhanced showers through at least the morning hours east of the
lakes.

Outlook...

Friday night through Sunday...mainly VFR.
Monday and Tuesday...VFR.

&&

Marine...
deepening low pressure tonight will makes its way from Lake Huron to
western Ontario while pushing a cold front across the lower Great
Lakes. Winds will strengthen in the wake of this front, with west to
southwest winds reaching gale force intensity after 03z on Lake Erie
and on the western third of Lake Ontario, and after 09z on the
eastern two thirds of Lake Ontario. Marine headlines are outlined
below.

As the still deepening storm system makes its way across northern
Quebec on Friday, gale force winds will remain in place across the
lower Great Lakes through at least the morning hours. Winds will
gradually subside from west to east during the midday and afternoon.

Expansive high pressure centered over the upper mid west Friday
evening will build across the lower Great Lakes Friday night. This
will continue to allow winds to weaken Friday night into Saturday.

&&

Tides/coastal flooding...
another Lakeshore flood event is expected tonight 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 tonight before
quickly diminishing during the day Friday. Sustained winds will
likely reach around 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 above low water datum, with this peak most likely
to occur between midnight and 3 a.M.

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. Sustained winds were much stronger on both lakes in
that 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.
Wind Advisory from 11 PM this evening to 10 am EST Friday for
nyz001>003-010>012-019-085.
Lakeshore Flood Warning from 11 PM this evening to 10 am EST
Friday for nyz010-019-085.
Marine...Gale Warning from 11 PM this evening to 10 am EST Friday for
lez020-040-041.
Small Craft Advisory until 1 PM EST Friday for loz030.
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.
Small Craft Advisory from 1 am to 4 PM EST Friday for
slz022-024.

&&

$$

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

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