Area Forecast Discussion
Issued by NWS Buffalo, NY

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336
FXUS61 KBUF 231142
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
642 AM EST Thu Nov 23 2017

.SYNOPSIS...
Weak bands of lake effect snow and rain will fall to the east and
then northeast of the Eastern Great Lakes today. Otherwise, an area
of high pressure, centered to our south, will influence our weather
today and tonight, with quiet condition today outside of the bands
of lake effect precipitation, and clearing skies tonight. After a
dry Friday and Friday evening, a cold front will bring the next
threat for rain showers overnight Friday and into Saturday...with
precipitation tapering off as snow Saturday night.

&&

.NEAR TERM /THROUGH TONIGHT/...
Surface high pressure is found this early morning over the lower
Ohio Valley, ridged northeastward across the Eastern Great Lakes.
Moisture trapped beneath a subsidence inversion is producing a
wealth of low clouds this morning, as evident on IR satellite
imagery. A few flurries are flying to the east of the Eastern Great
Lakes this morning, but overall not much returns on radar.

A mid level shortwave trough will cross the region today, while
surface high pressure, centered to our south, will pass across the
southern mid-Atlantic states. There will be just enough lake
instability in the lower levels to generate weak returns of lake
effect snow...and later in the day rain to the east and northeast of
the Eastern Great Lakes. Moisture will be limited due to the surface
high pressure nearby, and inversion heights will be low...but weak
lake effect snow may bring a fresh coating of snow to So. Erie
County, before mixing with and changing to rain late morning as the
band lifts northward towards the metro Buffalo area. Warming in the
lower levels combined with the loss of moisture from the snow growth
zone will favor drizzle/light rain, first off Lake Erie and later in
the morning off Lake Ontario.

Outside of the lake effect, today will feature mostly cloudy skies,
and highs in the mid 30s to a few lower 40s. The weak band of lake
effect precipitation will oscillate some over metro Buffalo this
afternoon and early evening before diminishing as mostly light snow
through the late evening hours. Meanwhile an approaching surface
trough to the north of Lake Ontario will enhance precipitation east
of Lake Ontario...with light snow falling through the overnight. An
inch or so of snow is possible across the higher terrain. Marginally
cold temperatures may maintain the bulk of precipitation as plain
rain closer to the Lake Ontario shoreline. Lows tonight will drop
back into 20s interior regions, to around 30 near the lakes.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
On Friday a ridge of high pressure will gradually slide eastward off
the Mid Atlantic coast. Meanwhile, there will be an increasing SSW
flow ahead of an approaching shortwave and cold front. This will
result in dry weather on Friday with warmer temperatures as warmer
mid-level air advects into the region. Highs will range from the mid
40s across the interior to the lower 50s across the lake plains
where there will be some warming due to downsloping. Despite the
warmer temperatures, it will be a bit breezy during the afternoon
with gusts 25 to 35 mph.

Model consensus brings the first of two cold fronts across the
region early Saturday. There will not be much moisture with this
front, but light but measurable amounts are likely late Friday night
into Saturday morning. Temperatures will be warm enough for all rain
due to the deep southerly flow. This also will keep temperatures
from dropping off much Friday night, with the forecast several
degrees warmer than consensus guidance due to the wind and
downsloping.

Air behind the front will not initially be cold enough to support
any lake effect precipitation, with the better part of Saturday
afternoon likely to be dry outside of lingering showers with the
front and associated shortwave. Temperatures aloft will gradually
fall behind the shortwave, perhaps just cold enough for some light
lake effect rain or snow showers through Saturday evening. Based on
a warmer model consensus the latest forecast is a bit slower to
develop a lake response.

A longwave trough pushing from eastern Ontario to Quebec will be the
driving force for a second cold frontal passage Saturday night.
However there is some uncertainty how far south this front will make
it. Some guidance (such as the 00Z NAM) are flatter with the
shortwave and as a result does not bring as much cold air into the
region. For example, at 12Z Sunday forecast 850mb temperatures
across Lake Ontario range from -8C to -12C. Either way, this will
support some lake response but how intense depends on how cold the
air mass is. Pops were scaled back slightly to reflect this shift in
guidance, but even so a period of lake effect snow is expected.

Snow amounts should be on the light side given the warmer air aloft
and relatively short period of time before temperatures warm with the
departure of the trough. The greatest amounts of snow will be in
locations which do well in a WNW flow which includes the Chautauqua
ridge, and areas southeast of Lake Ontario from Rochester to Oswego.
While accumulations are not expected to be significant in
themselves, it could be cold enough for the snow to be a little more
greasy so that untreated roadways would be more difficult to
navigate.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
Surface and mid-level ridging will build across western and central
New York Sunday night and Monday. A lowering subsidence inversion
will bring an end to accumulating lake effect snow southeast of both
lakes during the evening hours leveling just chance/slight chance
POPs through the overnight. BUFKIT time-height cross sections
indicate that plentiful lift and low level moisture will be
available through the night even with lake induced equilibrium
levels crashing below 5kft. This could be a set up for some freezing
drizzle as surface temperatures will be below freezing and lingering
moisture will be below the dendritic snow growth zone. This is
something to watch closely over the next few days. Otherwise expect
dry weather with low clouds breaking for some sun on Monday. Temps
with the riding aloft will make a run into the low 40s across WNY
but likely linger in the 30s east of Lake Ontario.

The surface and mid-level ridge axis shift east of our area by
Tuesday with southerly flow picking up ahead of what the GFS/GEM
show as another cold frontal passage for Tuesday night/Wednesday.
The ECMWF however does not show a front crossing our region. With
these differences in mid have only brought in slight chance POPs for
Tuesday night with Tuesday expected to largely be dry. The global
models do show a strong 50 knot low level jet crossing our region
Tuesday which could lead to some gusty winds with diurnal mixing.
Temps Tuesday under Southerly flow may make a run toward the upper
40s to low 50s with clouds possibly increasing from the west if the
GFS is correct with the approach of a front. Wednesday continues a
spread in guidance with the GFS/GEM showing -10C 850mb temps behind
a cold front and the EC showing +2C to +6C in zonal flow. Have
leaned toward GFS/GEM with chance POPs while surface temps have a
high bust potential with such spread. Have leaned toward a blend of
guidance for now yielding mid to upper 40s for highs but cloud be
cooler especially if the cold frontal passage occurs.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
For the 12Z TAFS, much of the region is VFR, though MVFR CIGS linger
across the So. Tier.

As winds become southwesterly today, there will remain enough lake
instability such that light lake effect snow may pass the KBUF/KART
airfields. Marginal temperatures may allow for some rain to mix into
the snow band. Outside of the bands of lake effect MVFR CIGS will
become VFR by early afternoon as drier air continues to erode the
MVFR CIG deck.

High pressure with associated fair weather and mainly VFR flight
conditions will pass by just to our south later tonight. Scattered
lake effect flurries, and MVFR CIGS will linger across KART.  A
tightening pressure gradient between this high pressure and nearing
weak surface trough to the north will maintain a moderate
southwesterly flow through tonight.

Outlook...

Friday...VFR.
Saturday...VFR/MVFR with rain showers likely.
Sunday...Mainly MVFR, localized IFR in -SHSN SE of the lakes.
Monday...VFR.

&&

.MARINE...
With high pressure crossing to the south of the lakes this early
morning, winds and waves have diminished such that the original
small craft advisory has been canceled.

A new set of Small Craft Advisories have been issued, as the
pressure gradient increases this afternoon...bring winds and waves
back above advisory levels. In addition a cold front will cross the
Eastern Great Lakes region Saturday, with a secondary cold front
Saturday night that will bring a prolonged period of SCA conditions
to Lake Erie, and the far western and eastern sections of Lake
Ontario. A lighter southerly fetch of winds Friday will allow for
non-SCA conditions along the nearshore waters of central Lake
Ontario.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory from noon today to 10 AM EST Sunday for
         LEZ040-041.
         Small Craft Advisory from 2 PM this afternoon to 10
         AM EST Friday for LOZ043-044.
         Small Craft Advisory from 2 PM this afternoon to 4 AM EST
         Monday for LOZ042-045.

&&

$$

SYNOPSIS...THOMAS
NEAR TERM...THOMAS
SHORT TERM...APFFEL
LONG TERM...SMITH
AVIATION...THOMAS
MARINE...THOMAS



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