Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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112
FXUS63 KMKX 110926
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
326 AM CST Sun Dec 11 2016

.TODAY AND TONIGHT...Forecast Confidence Is Medium.

The band of higher radar reflectivity that spans from southern
Minnesota to southern Wisconsin is associated with strong
700-600mb frontogenesis. This forcing is expected to lift north
later this morning, as the low amplitude mid level shortwave moves
across northern Wisconsin. Will expand the warning into our
northern tier of counties.

The upper level 250 mb jet structure shows the entrance region of
one strong jet max of 125 knots over the upper Great lakes. This
results in the northern shift of the snow band, due to upper level
divergence and 700 mb upward motion.

Meanwhile the southern sections should see lighter snow later
this morning. However upper level divergence and 700 mb upward
motion increases again south areas, especially southeast late
morning and afternoon, as the entrance region of the jet shifts
south. Expect a corresponding increase in snow. One problem will
be mid level drying, causing the dendritic zone to decrease later
today. This will be more pronounced in the western areas until
later in the afternoon.

The snow will be of the drier variety through the event, with
ratios starting around 20:1 and ending around 12:1. With this
being a prolonged event, rates will probably not exceed an inch an
hour for most of the event, though brief heavier bursts are always
possible. Storm totals are expected to be in the 7-9 inch range.

Will leave the Winter Storm Warning in place in the south for
now, but this may need to be changed later this morning or early
afternoon, especially southwest areas after the frontogenetic snow
bands decrease.

Travel will be hazardous, given the snow covered roads and colder
surface temperature, especially this morning.

.MONDAY THROUGH TUESDAY NIGHT...Forecast Confidence Is Medium.

Models are in decent agreement with weak high pressure passing to
the south of the area Monday. This will bring dry conditions to
the area. Area forecast soundings show some low clouds trying to
linger. Cold temperatures are expected once again.

NAM/GFS/ECMWF show 500 mb differential cyclonic vorticity
advection passing east through the area Monday evening, as a cold
front pushes through. The GFS is the only model showing any QPF
over the area. The NAM is also slower with the frontal passage
than the other models. For now, have lower end PoPs for Monday
evening.

Main issue this period will be the push of very cold temperatures
and wind chills into the area for Tuesday and beyond. Cold air
advection behind the front Monday night into early Tuesday will
bring these very cold temperatures into the region. Arctic high
pressure in the northern Plains will keep this very cold airmass
in place through the week.

Expect temperatures to plummet into the single digits above zero
Monday night, and not rise much on Tuesday. Lows in the single
digits below zero look likely for Tuesday night away from the
lake. Slowly tightening pressure gradient Tuesday into Tuesday
night should bring increasing west winds. This should bring wind
chills into the teens below zero in most areas.

.WEDNESDAY THROUGH SATURDAY...Forecast Confidence Is Medium.

ECMWF/GFS continue to show the Arctic high pressure system
sliding eastward, south of the area, Wednesday into Thursday
night. The pressure gradient should remain fairly tight during
this time, allowing for elevated gusty west northwest winds. The
very cold temperatures will continue, with wind chills in the
teens below zero Wednesday. They should dip into the 15 below to
25 below zero range Wednesday night, before slowly improving into
Thursday night.

ECMWF/GFS then show a strong low pressure system from the central
Rockies into the central Plains Friday, then shifting northeast
into the eastern Iowa to southeast Wisconsin area Friday night.
The low then moves northeast of the area Saturday, with strong
cold air advection once again over the region.

Depending on where this low tracks, southern Wisconsin could see
several inches of accumulating snow, or a mix of snow and rain.
For now, went all snow in forecast until better model agreement
can be found. Certainly another system to watch for as we get into
the later portions of the week.

&&

.AVIATION/12Z TAFS/...

Steady snowfall will persist through the morning. The snow should
briefly lighten after 8 am Sunday, especially in south central
Wisconsin. Southeast WI could see another round of moderate snow
during the mid afternoon hours. Snow will end later Sunday
afternoon into early Sunday evening.

Persistent visibilities of 1 to 2 miles though the event are
likely, with periods down to 1/2 mile probable as well. Ceilings
should be in the 1 to 2 thsd ft range until afternoon. Expect cigs
to lower to IFR by Sunday evening, as low pressure tracks across
Wisconsin.

The snow will be of the drier variety through the event, with
ratios starting around 20:1 and ending around 12:1. With this
being a prolonged event, rates will probably not exceed an inch an
hour for most of the event, though brief heavier bursts are always
possible. Storm totals are expected to be in the 7-9 inch range.

&&

.MARINE...

Southerly winds ahead of approaching low pressure will likely
gust to 25 knot at times today. This will build waves of 3 to 5
feet across the nearshore waters, especially toward Sheboygan.

Westerly winds will then become gusty behind the low and
associated cold front Sunday evening, with higher gusts lingering
into Monday morning. The waves will be lower with the offshore
winds this evening into Monday, except for higher waves toward
open waters. A Small Craft Advisory is in effect from 9 am CST
today to 10 am Monday.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...WINTER STORM WARNING until 6 PM CST this evening for WIZ056-062-
     063-067>070.

     WINTER STORM WARNING until 8 PM CST this evening for WIZ046-047-
     051-052-057>060-064>066-071-072.

LM...SMALL CRAFT ADVISORY from 8 AM this morning to 9 AM CST Monday
     for LMZ643>646.

&&

$$

TODAY/TONIGHT AND AVIATION/MARINE...Hentz
MONDAY THROUGH SATURDAY...Wood



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