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000
FXUS61 KBUF 211118
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
618 AM EST Mon Jan 21 2019

.SYNOPSIS...
A northwesterly flow of bitterly cold air will result in dangerously
low wind chill values today, and another very cold night tonight.
The arctic airmass will finally move out of the area on Tuesday, and
this will be followed by low pressure which will track to our north
on Wednesday. This will result in a short period of above normal
temperatures along with some mixed precipitation mid-week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Bitterly cold conditions will prevail throughout the period.
Temperatures will be below zero in most locations through mid-
morning. This combined with winds gusting to 30 mph in spots will
result in wind chills of 20 to 30 below in most areas, with 30 to 40
below zero across the North Country and interior portions of the
Southern Tier through this morning. Temperatures will only rise into
the single digits this afternoon, except across the North Country
where temperatures will remain below zero. This will result in a
modest improvement, but still bitterly cold conditions this
afternoon. Consequently, Wind Chill Advisories and Warnings remain
in effect for this potentially life threatening risk.

Meanwhile, lake effect snow continues this morning southeast of
Lake Ontario, and to a lesser extent Lake Erie. These extend
roughly 15 miles inland from the lakes, but vary in intensity
with numerous narrow tendrils embedded within. It`s also worth
noting that these are developing below a low capping inversion
of 3-5 kft so radar will not effectively sample this far away
since the beam will overshoot the snow. However, webcams and
satellite imagery confirm fairly persistent snows southeast of
Lake Ontario, and to a lesser off Lake Erie. Since we have
effectively lost our dendritic growth zone in this arctic
airmass, snowfall rates from the resulting plates and columns
will be under a half inch hour. However, these are effective in
lowering visibility, and persistence still could bring another 1
to 3 inches of snow today south of Lake Ontario. There also
could be areas of blowing snow. A Winter Weather Advisory
remains in effect for counties adjacent to and south of Lake
Ontario. Most of the snow accumulation will occur thorugh this
morning before the upper level trough and the core of coldest
air aloft moves east into New England.

Surface high pressure centered across Ohio this evening will build
eastward across our region tonight. Winds will maintain longest east
of Lake Ontario, where wind chill headlines may have to be extended.
Wind chills aside, it will be another very cold night. Although
temperatures aloft will be considerably warmer, the surface high
will provide conditions favorable for radiational cooling.
Temperatures will again fall below zero in most locations, except
along the immediate lakeshores. Lows should run 10 to 20 below
across the North Country, with even colder readings possibly in some
spots. Otherwise, leftover lake snow showers southeast of Lake
Ontario should taper off to flurries while the remainder will
experience mainly clear skies.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
Tuesday will start very cold with a +2 SD surface high pressure
centered over the region. This surface high will slide to the mid-
Atlantic coastline through the day and a southerly flow will
commence a moderating temperature trend.

Tuesday night surface low pressure in the base of a mid level trough
will advance from the midwest to the central Great Lakes. A strong
LLJ will develop ahead of this low pressure, and this jet will aid
in rising temperatures through the night and bringing above freezing
temperatures to the region late Tuesday night and into Wednesday.

Precipitation wise, an initial broken area of light snow is possible
late Tuesday night on the leading edge of the LLJ. The precipitation
is then expected to become more widespread towards daybreak across
far WNY and the Saint Lawrence Valley as moisture deepens and the
surface low draws closer to our region. This precipitation will then
spread over the Genesee Valley and Finger Lakes region Wednesday.

This LLJ will bulge a layer of much warmer air aloft across WNY (850
hPa +2 to +5C) while surface temperatures around freezing lag
behind. A wintry mix is expected, with snow transitioning to
sleet/freezing rain as we warm aloft, and then plain rain briefly
spreading across WNY as surface temperatures warm into the upper 30s
to lower 40s. Cooler air to the north may linger the precipitation
as all snow across the North Country. Here there is potential for 2
to 4 inches of snow accumulation by Wednesday evening.

There is still uncertainty as to how fast and how much we warm
aloft...but for now will mention the risk of freezing rain in the
HWO for WNY. Of note, the recent extreme cold spell and prospects of
untreated roads may elevate the freezing rain potential...with
freezing rain on frozen ground surfaces that will lag behind in
warming.

By Wednesday night the surface low cutting to the north of Lake
Ontario will push a cold front across our region, changing the plain
rain back to all snow. This front will slowly move across our region
as a wave of low pressure will likely form on the front in the
South. As this wave rides northward, precipitation associated with
it may brush by our eastern zones.

Snow accumulation behind the front will be little to none for the
lower terrain, however higher terrain to the east of both lakes may
receive a few inches oweing to lake enhancement and upslope effects.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
The pattern will turn much more wintry again for the end of the week
and next weekend after our brief warm-up on Wednesday. The +PNA
pattern will re-amplify significantly by next weekend across the
North American continent, with a deep trough carving out in the
east. This will push temperatures to well below average again. This
cold pattern will have staying power, with long range outlooks and
ensembles suggesting it lasting through the end of the month and
beyond.

Looking at the details, on Thursday a complex frontal zone will
advance to the east coast. A wave of low pressure will be running
northeast along the boundary, and associated ascent from this wave
and the approaching mid level shortwave will likely allow
precipitation to linger on the cold side of the boundary. By
Thursday morning all areas should be back to snow, with some minor
accumulations possible. The synoptic snow will taper off from west
to east through the day, with some minor lake effect snow showers
possible later Thursday afternoon and Thursday night southeast of
the lakes as colder air aloft arrives. High temperatures Thursday
will be in the lower 30s in most locations, and lows Thursday night
will be in the upper teens to lower 20s.

Late Thursday night and Friday a strong mid level trough and
associated surface low/cold front will cross the region, marking the
leading edge of the return to much colder temperatures. This system
will bring a chance of snow showers areawide, with potential for
lake enhancement east of the lakes.

The cold becomes well established by the weekend. Model guidance
begins to diverge with the handling of clipper shortwaves moving
through the mean longwave trough, but in a general sense one or two
weak systems will continue to support light snow chances through the
weekend. There may also be lake effect potential next weekend,
although given the model differences with the handling of the
clipper systems there is a good deal of uncertainty with respect to
placement and strength.

High temperatures by the weekend will be back into the teens in most
locations, with lows in the single digits, and below zero east of
Lake Ontario.

&&

.AVIATION /12Z MONDAY THROUGH FRIDAY/...
A northwesterly flow of bitterly cold air will continue to generate
countless bands of light lake effect snow southeast of Lakes Erie
and Ontario through this morning. Although snow accumulation
will be light, the very small snowflakes will be very effective
in lowering visibility. Conditions will vary anywhere from MVFR
to LIFR in and out of these bands during this time. The most
persistent snows will be at KIAG/KROC/KJHW.

Conditions will improve this afternoon as drier air moves in
and winds diminish. MVFR cigs will gradually dissipate with
mainly VFR conditions expected by this evening. High pressure
will build across the area late tonight with VFR flight
conditions.

Outlook...
Tuesday...VFR.
Tuesday night and Wednesday...MVFR/IFR in snow
changing to mainly rain.
Thursday...VFR to MVFR with scattered snow showers.
Friday...VFR to MVFR in scattered to numerous snow showers...
with IFR possible in more numerous snow showers east of the
lakes.

&&

.MARINE...
A relatively tight surface pressure gradient will remain in place
over the Lower Great Lakes through this evening. Winds will diminish
from west to east starting this afternoon as high pressure builds in
from Ohio. This will keep Small Craft Advisory conditions in place
throughout the Lower Great Lakes...with enough wave action to
continue to support the Heavy Freezing Spray Warning.

The area of high pressure will drift across the Lower Great Lakes
tonight. This will allow winds, waves, and any lingering freezing
spray to diminish. Light winds will then gradually freshen over the
lakes during the day Tuesday, as the large surface high will move
east into New England.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Wind Chill Warning until 7 PM EST this evening for NYZ006>008-
     012>014-019>021-085.
     Winter Weather Advisory until 11 AM EST this morning for
     NYZ001>006.
     Wind Chill Advisory until 7 PM EST this evening for NYZ001>005-
     010-011.
MARINE...Heavy Freezing Spray Warning until 10 AM EST this morning for
         LEZ040-041.
         Small Craft Advisory until 1 PM EST this afternoon for
         LEZ040-041.
         Small Craft Advisory until 10 AM EST this morning for
         LOZ030.
         Heavy Freezing Spray Warning until 6 PM EST this evening
         for LOZ042>045-062>065.
         Small Craft Advisory until 1 AM EST Tuesday for LOZ042>044.
         Small Craft Advisory until 7 PM EST this evening for
         LOZ045.

&&

$$

SYNOPSIS...Apffel
NEAR TERM...Apffel
SHORT TERM...Thomas
LONG TERM...Hitchcock
AVIATION...Apffel
MARINE...Apffel