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FXUS63 KMKX 181056
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
456 AM CST Fri Jan 18 2019

.SHORT TERM...

Today Through Saturday...Forecast Confidence is Medium.

We haven't seen significant changes to model precip amounts with
the last couple of runs. If anything, amounts went up near the
WI/IL border and lake enhanced snow may affect Sheboygan county a
little longer than previously anticipated. We rolled the Winter
Storm Watch areas into a Warning with the exception of Ozaukee
County, then added Sheboygan and Ozaukee as Advisories. The other
Advisory counties remain unchanged.

Our snowfall amounts fall right in the middle of where the models
suggest. Looking at the WPC probability graphics on our winter
weather page, the forecast snowfall amounts fall in between the
50th and 75th percentiles. We are a little on the higher side of
guidance because many models do not handle the lake effect portion
very well since it is small scale.

Frontogenesis and upper divergence with the right entrance region
of the upper jet are the key players for southern Wisconsin and
northern Illinois with this event. The average position of the mid
level fgen band between the models is actually on the IL side of
the border. There is fgen expected around 850mb that should be
over southern WI this evening. The meso models are focusing their
higher reflectivity over northern IL. So there remains
uncertainty about whether or not the warning snowfall amounts will
make it into the southern tier of counties in WI.

The other key player is the lake enhancement component with a
long fetch of northeast winds with a sufficient lake-850mb temp
difference. This will add another couple of inches on to the
synoptic snow expected, thus highest snowfall amounts are
anticipated over eastern Kenosha county and areas into northeast
IL.

The model soundings show a deep dendritic growth zone over south
central WI for the last half of the snow, after midnight tonight
into Saturday morning. Then dry air moves in from the northwest
quickly to end the snow. There is a chance the snow could over-
perform during this time if we get higher snow ratios with the
deep DGZ, but went with more conservative amounts for now.

Saturday night through Sunday night...Forecast confidence medium.

Brisk nnely boundary layer flow will be slow to back due nly for
Sat nt. Thus, a lake effect snow band will continue to affect the
far ern portions of Milwaukee, Racine, and Kenosha Counties. A
Winter Storm Warning remains in effect until midnight. The brisk
and gusty winds will cause some blowing and drifting snow. Very
dry air at 850 mb and above may limit the intensity of the lake
effect snow.

A sfc ridge and arctic air will then be in place for Sun-Sun nt.
Small chances for Lake effect snow over far ern WI as the flow
briefly becomes sely.



.LONG TERM...Monday through Thursday...Forecast confidence medium.

A sly flow and warm, moist advection will develop for Mon into Tue
as a fairly strong upper trough moves into the central Great
Plains and toward se WI. There is uncertainty on the strength of
the sfc low but some accumulating snow appears likely with
possibly a period of rain and snow mixture over far se WI. The low
pressure area will quickly move away with cold high pressure in
place for Wed and possibly into Thu.


&&

.AVIATION(09Z TAFS)...

MVFR ceilings, some down to 1500 feet, are gradually moving out
from northwest to southeast early this morning. A period of VFR
conditions with light northerly winds are then expected, becoming
northeast by midday.

The snow will spread eastward into southern WI this afternoon and
early evening. Expect moderate snow with visibility values of 1
mile or less in southern parts of the area Friday night into
Saturday morning, with ceilings of 1000 feet or less. These
conditions should remain Saturday afternoon into Sunday near Lake
Michigan, depending on where the lake effect snow band sets up.

Snowfall rates could reach 1/2 to 1 inch per hour in the heaviest
snow bands, mainly in toward the Illinois border and near Lake
Michigan. Stay tuned for later updates on amounts, intensity and
timing of the snow as we get closer to the event.

&&

.MARINE...

Nearshore Waters...Gusty onshore winds will develop late this
evening and persist into Sunday across the nearshore waters of
Lake Michigan. Frequent gusts of 25 to 30 knots are expected
during this time. Waves should build to 6 to 9 feet during this
time as well. A Small Craft Advisory is in effect. Freezing spray
is likely during this period as well.

May see gusty south winds up to 25 knots Monday into Tuesday, as
another low pressure system moves toward and through the region.

Open Waters...Gusty northeast to north winds will develop tonight
and persist into Sunday across the open waters of Lake Michigan.
Frequent gusts to 30 knots are expected during this time. May see
a few gusts near gale force Saturday over the southern half of
the lake. Will continue to hold off on a Gale Warning and see if
these winds increase in the models. Waves will build during this
time. Freezing spray is likely as well.

May see gusty south winds up to 30 knots Monday into Tuesday, as
another low pressure system moves toward and through the region.
Waves should build again during this period.


&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Storm Warning from 6 PM this evening to midnight CST
Saturday night for WIZ066-071-072.

Winter Storm Warning from 3 PM this afternoon to 6 AM CST
Saturday for WIZ067>069.

Winter Weather Advisory from 3 PM this afternoon to 6 AM CST
Saturday for WIZ056-062-063.

Winter Weather Advisory from 6 PM this evening to noon CST
Saturday for WIZ052-059-060-064.

Winter Storm Warning from 6 PM this evening to noon CST Saturday
for WIZ065-070.

LM...Small Craft Advisory from 9 PM this evening to 3 PM CST Sunday
for LMZ645-646.

Small Craft Advisory from 9 PM this evening to 10 AM CST Sunday
for LMZ643-644.

&&

$$

Today/Tonight and Aviation/Marine...Cronce
Saturday through Thursday...Gehring
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