Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 141803 AAB
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1203 PM CST Sun Jan 14 2018

.UPDATE...

Continuing to evaluate the need to raise snowfall accumulations in
the northern and eastern areas near Lake Michigan. This would be
due to the lake enhanced snow band pivoting southward through
these areas Monday into Monday evening, and for lake effect snow
expected later Monday night into Tuesday morning. May need to
raise amounts a few inches in these areas.

Also contemplating the need for a Winter Storm Warning for
Sheboygan south to Milwaukee County, given the possible higher
amounts and impact on the Monday/Tuesday morning commutes. The
lake enhanced band will continue to be the variable that will be
most tricky to pin down, thus the most uncertainty.

Wood

&&

.AVIATION(18Z TAFS)...

Some flurries may move into western portions of the area this
afternoon. No accumulations are expected with this. South winds
are expected this afternoon, with overcast skies spreading east by
the middle afternoon hours.

The snow is expected to spread eastward across the area between
00Z and 03Z Monday. A long duration powdery snow event is expected
tonight into Monday night/Tuesday morning. Ceilings should remain
in the 2000 to 2500 foot range tonight into Monday night, possibly
a bit lower at times. Visibility values should be in the 1 to 2
mile range during this time, again possibly a bit lower at times.

Main uncertainty here will be lake enhanced snow band that may
pivot southward across the northern and eastern portions of the
area Monday into Monday night. There may be moderate to heavy snow
rates of 1 inch per hour or greater associated with this band.
Depending on how quickly it moves through the area will determine
how much more snow it will drop.

For now, expecting a general 4 to 7 inches of snowfall
accumulations tonight into Monday night/Tuesday morning. The
lowest amounts will be southwest of Madison, and highest toward
the Sheboygan area and near Lake Michigan. Amounts may need to be
raised in the north and east near Lake Michigan. Snowfall rates
should be up to 1/4 inch per hour, with 1/2 inch per hour rates
possible at times.

South winds tonight will veer west Monday morning and northwest
in the afternoon. They may become more northerly Monday night into
Tuesday. They may have gusts in the 15 to 20 knot range at times.

Wood

&&

.PREV DISCUSSION... (Issued 1008 AM CST Sun Jan 14 2018)

UPDATE...

No changes are planned at this time for the Winter Weather
Advisory and the associated snow amounts for tonight into Tuesday
across the area. The 12Z models that are available so far are
similar to the previous model run with general trends.

The one big variable will be where the mesoscale snow band
associated with surface to 850 mb frontogenesis/convergence will
set up and cross the area Monday into Monday evening. Several
synoptic and mesoscale models have this feature pivoting counter
clockwise as it slides southward across the northern and eastern
counties.

There looks to be lake enhancement with this band, which may add
several inches of snow accumulation to wherever this band moves
across. Its transient nature may limit these higher amounts
somewhat, and there is some uncertainty here with where these
higher amounts may occur. Right now, it may be across the
northeastern and far eastern counties. This could affect total
snow accumulations in these areas, and will continue to evaluate
need to adjust amounts.

Wood

MARINE...

Small Craft Advisory remains in effect from 6 PM CST this evening
until 6 AM CST Monday morning south of Port Washington, and until
9 AM CST Monday morning north of there. The pressure gradient is
expected to tighten during this period, as low pressure approaches
the area from the west.

This will bring increasing south winds, with gusts of 25 to 30
knots at times. This will also bring building waves of 3 to 6 feet
tonight, before gradually subsiding to 2 to 4 feet on Monday.

North to northwest winds will approach Small Craft Advisory
levels at times Monday night into Tuesday, as the low gradually
moves away from the region. South to southwest winds Wednesday
into Friday will approach Small Craft Advisory levels as well.

Wood

PREV DISCUSSION... (Issued 533 AM CST Sun Jan 14 2018)

UPDATE...The forecast is on track for south winds and milder
temperatures today and tonight, and a long duration snowfall from
this evening through Mon nt. A Winter Wx Advisory is in effect.

AVIATION(12Z TAFS)...VFR conditions today, then light snow
spreading across srn WI this evening and continuing into Mon. Cigs
will fall to 1-3 kft early this evening with vsbys of 1-2SM.

PREV DISCUSSION... (Issued 349 AM CST Sun Jan 14 2018)

DISCUSSION...

Today and Tonight...Forecast Confidence is High.

Arctic high pressure will shift ewd today with sly winds and warm
advection beginning. Clouds will increase later this morning via
the warm advection with increased warm advection and snow
tonight. This is in response to a nwly 120 kt jet digging an
upper trough from Canada to WI. The upper wave amplifies including
warm advection at the jet level along with DCVA. The snow will
continue into Mon nt with several inches of powdery snow. Thus a
Winter Wx Advisory has been issued for tnt-Mon nt. Temps will warm
into the teens today with little change tnt.

Martin Luther King Jr Day and Tuesday - Confidence...Medium
Long duration snow event will be continuing through the morning
rush on Monday and probably the evening rush as well. So the
advisory will continue into Monday night. Plenty of dynamics
upstairs as system gradually strengthens. 700 low wraps up across
SC WI. The 500 low comes across WI Monday with plenty of embedded
vorticity maxima pivoting through. The north/south oriented lower
level trough shifts to our southeast and then becomes nearly
east/west Monday night into Tuesday. This sets up favorable
convergence especially in the eastern cwa with a favorable flow
off the lake setting up as well, which will bolster some snow
amounts in the east and esp close to the lake. So expecting the
snow potential to last into Tuesday morning near the lake due to
the lingering effects of the convergence associated with the
trough and lake effect. Looking to event totals to be in the 4 to
6 inch range.

Wednesday through Friday - Confidence...Low to Medium
Lingering of influence of low level thermal trough and fresh snow
cover will set up another chilly day on Wednesday, however a more
pronounced warm air advection regime sets up for Thursday and
Friday. With low pressure proggd to organize in the central or
northern Plains Friday models are showing the potential for the
warmer airmass to be sustained with south or southwest 925/850
flow. By Saturday we could see some isentropic induced
precipitation set up in conjunction with an east/west baroclinic
zone associated with the evolving low though there is still much
model variability on this evolution.

AVIATION(09Z TAFS)...VFR conditions today, then light snow
spreading across srn WI this evening and continuing into Mon. Cigs
will fall to 1-3 kft early this evening with vsbys of 1-2SM.

MARINE...A Small Craft Advisory is in effect tonight into Mon AM
for brisk south winds. High waves will also develop north of Port
Washington.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory from 6 PM this evening to midnight CST
     Monday night for WIZ046-047-051-056>058-062>064-067>070.

     Winter Weather Advisory from 8 PM this evening to 6 AM CST
     Tuesday for WIZ052-059-060-065-066-071-072.

LM...Small Craft Advisory from 6 PM this evening to 6 AM CST Monday
     for LMZ644>646.

     Small Craft Advisory from 6 PM this evening to 9 AM CST Monday
     for LMZ643.

&&

$$

Update...Wood
Today/Tonight and Aviation/Marine...Gehring
Monday THROUGH Saturday...Collar



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