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Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
514 PM CST Tue Jan 22 2019

Update...

There's nothing meaningful to add to the recently issued
discussion. The new NAM and GFS aren't offering any surprises. The
event has just been delayed, but is expected to peak from mid
evening into Wednesday morning. The colder solutions are
highlighting more snow and less potential for any more freezing
type precipitation. The shift south may also keep amounts lower up
around Sauk, Marquette, Green Lake and Fond Du Lac counties. Not
ready to make headline adjustments up there, but will be looking
at it over the next few hours.

&&

Aviation(00z tafs)...

Expect widespread IFR ceilings/visibilities through 18z Wednesday due to a
long duration snowfall across southern Wisconsin. The low pressure
responsible for the snow is tracking farther south and therefore
it looks like the threat for freezing drizzle/rain is very
minimal, or non-existent now. We expect some of the heaviest snow
will occur from mid evening into Wednesday morning. The guidance
is also suggesting a band of snow may organize Wednesday morning,
from about 12-16z, that could bring a period of heavy snow. Winds
will be light and variable early this evening, then become
northerly and increase slowly through the night. Gusty northwest
winds are expected on Wednesday with gusts to 25kts possible at
times. Total accumulations should be in the 5 to 7 inch range and
ending by mid day on Wednesday.

&&

Previous discussion... (issued 350 PM CST Tue Jan 22 2019)

Short term...

Tonight and Wednesday...forecast confidence is medium to high.

All short term guidance looking a little deeper and sharper with
mid-level short wave trof that passes across southern Wisconsin
late tonight into Wednesday morning. This short wave is currently
in the Southern Plains, and latest water vapor imagery shows a
nice plume of deep mid-level moisture from Texas extending into the
Great Lakes.

Warm air and moisture advection beginning to shift east as low
level jet pivots into the central Great Lakes. However, some
enhancement on radar imagery over northern Illinois into southeast WI as
lingering vestiges of better low level convergence and deepening
moisture meet up across the area.

Despite better low level convergence pivoting off to the east
this evening, lingering baroclinic zone across the area along with
approaching wave will continue to generate mostly snow across the
area tonight into Wednesday morning. Latest infrared imagery showing
surge of colder air aloft which will help change the patchy
freezing drizzle over to snow during the late afternoon and early
evening as ice crystals begin to fall into the deepening cloud
bearing layer.

Strongest synoptic scale lift associated with the passing wave
will be later tonight into Wednesday morning. Snowfall rates of
one half inch to one inch per hour will be possible. Impressive
layer q-vector convergence exceeding 30 units moves across
southern WI during this period.

850h organized low pressure passes across southeast WI around 12z
Wednesday, with axis of heavier quantitative precipitation forecast just to the northwest of the
track. Hence axis of highest quantitative precipitation forecast and snowfall totals have been
nudged southeast, focusing more on south central into east central
and most of southeast Wisconsin. Added Racine and Kenosha
counties to Winter Storm Warning. Despite lowering snowfall in the
far northwest including The Dells and Westfield, too close to
heavier snowfall axis at this time to downgrade Winter Storm
Warning to advisory.

Expect snow to rapidly diminish from mid-morning Wednesday to the
early afternoon as mid-level deformation zone shifts rapidly to
the northeast.

Wednesday night...forecast confidence is medium.

A brief period of quiet weather is expected, ahead of the Arctic
cold front moving southeast toward the area. Light winds with
party cloudy skies should allow for temperatures to tumble into
the single digits above zero. If clouds linger more during this
time, lows would remain several degrees warmer.

Long term...

Thursday through Saturday...forecast confidence is high.

Models remain in very good agreement with the Arctic cold front
plowing southeast through the area Thursday morning. Strong cold
air advection behind it Thursday afternoon and night on brisk
northwest winds will bring in the coldest airmass of the winter
season so far. This frigid airmass will remain in place into
Saturday.

Temperatures will fall Thursday afternoon and night, with lows
Thursday night into the 7 below to 15 below zero range. Highs
Friday will only reach around zero, with lows of 10 below to 18
below zero Friday night. Saturday will see highs between zero and
5 above zero.

These very cold temperatures combined with the expected winds
will bring bitter cold wind chills of 20 below to 32 below zero
Thursday night and Friday night. Wind chills Friday and Saturday
will only be in the teens below zero. Thus, a Wind Chill Advisory
will be needed eventually for Thursday night into Saturday. If
temperatures and wind chills get a little colder, reaching 35
below zero or colder, a wind chill warning may need consideration.

Saturday night through Tuesday...forecast confidence is high.

Temperatures may modify into the teens for highs Sunday into
early next week, with lows in the single digits above to below
zero. Wind chills should still be below zero during this time,
with bitter cold values of 20 below zero or lower possibly
returning Monday night into Tuesday morning. Thus, very cold
temperatures and wind chills will continue into early next week.

Models remain in good agreement with a weaker clipper system
moving east southeast through the region Saturday night, with a
stronger clipper for Sunday night into Monday. The latter system
may bring our next shot at accumulating snowfall to the area.

Aviation(21z taf updates)...

Expect areas of light freezing rain and drizzle to transition to
mostly light snow late this afternoon and evening. Periods of snow
are then expected overnight into Wednesday morning. Mainly light
snow is expected. Widespread ceilings of IFR or low MVFR are
expected for much of the period with visibilities mostly less than
3 miles. Highest snowfall rates expected over parts of southern
WI from late evening through early morning Wednesday.

Marine...

Nearshore waters...

Small Craft Advisory continues until 03z Wednesday across the
nearshore waters of Lake Michigan. Winds have weakened
considerably over the past few hours, and will remain light into
this evening. Lingering elevated waves will subside by middle
evening as well. Thus, moved ending time of Small Craft Advisory
up to 03z Wednesday.

May see north to northwest winds gusting to 25 knots at times,
along with waves of 3 to 5 feet, on Wednesday. A Small Craft
Advisory may be needed.

More gusty west to northwest winds should occur Thursday into
Thursday night, and again at times over the weekend into early
next week. The very cold airmass moving into the region with the
winds during this time may bring an extended period of heavy
freezing spray.

Wood

Open waters...

The Gale Warning has been cancelled for the open waters of Lake
Michigan. South winds have weakened fairly quickly this
afternoon, and gales are no longer expected. Winds should continue
to weaken into this evening.

Winds will shift north to northeast tonight into Wednesday
morning, becoming northwest Wednesday afternoon. Some gusts to 30
knots are possible, along with some freezing spray.

More gusty west to northwest winds should occur Thursday into
Thursday night, and again at times over the weekend into early
next week. The very cold airmass moving into the region with the
winds during this time may bring an extended period of heavy
freezing spray.

Wood

&&

Mkx watches/warnings/advisories...
WI...Winter Storm Warning until noon CST Wednesday for wiz046-047-051-
052-056>060-062>072.

Lm...Small Craft Advisory until 9 PM CST this evening for lmz643>646.

&&

$$

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