Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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989
FXUS63 KMKX 132312
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
512 PM CST Sat Jan 13 2018

.UPDATE...

Mostly clear skies and very cold with light winds.

&&

.AVIATION(00Z TAFS)...

High pressure will move off to the southeast Sunday. Northwest
winds are expected to gradually weaken into tonight, and become
light and variable later tonight into early Sunday morning. Mostly
clear skies are expected.

South winds will increase later Sunday morning into the afternoon,
ahead of low pressure moving toward the area. Clouds will increase
during this time, with ceilings gradually lowering but remaining
VFR category.

Snow should move east into the area early Sunday evening,
lingering through the night. The snow should linger Monday
morning in the northern and eastern portions of the area, with
chances remaining Monday afternoon into early Tuesday morning.
There may be break or the ending of the snow for southern and
western portions of the area Monday morning.

Right now, expecting anywhere from around 2 inches southwest of
Madison, to around 5 inches toward the Sheboygan area. The snow
will be powdery.

&&

.PREV DISCUSSION... (Issued 246 PM CST Sat Jan 13 2018)

SHORT TERM...

Tonight And Sunday...Forecast Confidence Is Medium.

Models are in good agreement with bringing high pressure southeast
across the region tonight, then sliding to the southeast on
Sunday. Light winds and mostly clear skies should allow for decent
radiational cooling across the area.

Went with the colder consensus MOS guidance for lows tonight,
which bring single digits below zero across most areas away from
the lake. Lows could get a bit colder than currently forecast, as
these situations tend to allow for rapid cooling. Wind chills
will be in the teens below zero.

Clouds will gradually increase Sunday, as warm air advection
develops over the area. South winds should increase as well, which
should bring highs into the middle to upper teens.

Sunday Night Through Tuesday...Forecast Confidence Is Medium.

Models remain in pretty good agreement with trends for the snow
during this period. It appears that the air column will saturate
from west to east during the early evening hours. Upward vertical
motion will be aided by the warm air advection Sunday night, and
differential cyclonic vorticity advection later Sunday night into
Monday morning. Decent low level frontogenesis response also
pushes through the area with the passing low later Sunday night
into Monday morning.

Thus, continued high PoPs for Sunday night, and lingered them in
the east Monday morning. Dry slot then works into parts of the
southern and western counties on Monday, which may end the snow
there in the morning.

Areas to the north and east should see continued chances for
light snow Monday afternoon into perhaps Tuesday morning. This is
due to a second round of upward vertical motion from pivoting low
level frontogenesis response fields across the northern and
eastern counties. For now, the PoPs in these areas Monday
afternoon into Monday night may need to be raised if the models
remain consistent, and there could be a little more snow than
forecast for this period.

A total powdery snowfall of 2 to 5 inches still looks reasonable
for Sunday night into early Tuesday. This is using higher end snow
to liquid ratios with a relatively deep dendrite zone that is
saturated for Sunday night into Monday morning, and a somewhat
shallower dendrite zone Monday afternoon into early Tuesday.

No winter weather headlines are planned at this time, but may be
needed in later forecasts with the snow occurring during the
morning commute on Monday. It may linger into the evening commute
in the north and east Monday evening with that second round, and
perhaps into Tuesday morning.

Temperatures will remain cold during this period, with wind chills
perhaps reaching Wind Chill Advisory criteria in the southwestern
counties later Monday night/Tuesday morning.

LONG TERM...

Tuesday Night Through Saturday...Forecast Confidence Is Medium.

Models are showing the 500 mb flow transitioning from
northwesterly Tuesday night into Wednesday, to zonal later
Thursday, and southwest by the weekend. High pressure to the
southeast of the region by the middle to late portions of the
week should bring a period of steady warm air advection. This may
bring temperatures back to near or above seasonal normals by late
in the week.

Models show some hints of a passing 500 mb shortwave trough
Thursday night with light QPF, as well as Saturday with more
moisture transport into the region. However, there is too much
disagreement with timing and placement of these features to
mention in forecast at this time.

AVIATION(21Z TAFS)...

High pressure will slide southeast through the region into
tonight, before moving to the southeast on Sunday. Northwest
winds are expected to gradually weaken into tonight, and become
light and variable later tonight into early Sunday morning.
Mostly clear skies are expected, with cold temperatures.

South winds will increase later Sunday morning into the afternoon,
ahead of low pressure moving toward the area. Clouds will increase
during this time, with ceilings gradually lowering but remaining
VFR category.

The snow should move east into the area early Sunday evening,
lingering through the night. The show should linger Monday
morning in the northern and eastern portions of the area, with
chances remaining Monday afternoon into early Tuesday morning.
There may be break or the ending of the snow for southern and
western portions of the area Monday morning.

Right now, expecting anywhere from around 2 inches southwest of
Madison, to around 5 inches toward the Sheboygan area. Rates
should be around a tenth of an inch per hour, perhaps up to 1/4
inch per hour at times. The snow will be powdery. South winds
Sunday night will gradually veer to the west and northwest Monday
afternoon and evening.

MARINE...

Northwest winds will continue to gradually weaken into tonight, as
high pressure moves southeast through the region.

Another period of brisk winds and high waves are possible late
Sunday afternoon into Monday morning, as low pressure moves
toward and through the region. Gusty south winds and high waves
are possible late Sunday afternoon into Monday morning, as the low
approaches. A Small Craft Advisory may be needed.

Gusty west to northwest winds are possible later Monday afternoon
into Tuesday morning, as the low departs the region. Some
freezing spray is possible Monday as well. Another Small Craft
Advisory may be needed.

Winds and waves may reach Small Craft Advisory levels at times
later in the week.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...None.
&&

$$

Update...Hentz
Tonight/Sunday and Aviation/Marine...Wood
Sunday Night through Saturday...Wood



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