Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 151828 AAB
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
128 PM CDT Sun Apr 15 2018

.UPDATE...

Steady snowfall is beginning to wind down from south to north
early this afternoon. This trend will continue through mid
afternoon, with mainly light snow then late afternoon into
tonight. Could see a little freezing drizzle at times in the east
this afternoon into the evening.

&&

.AVIATION(18Z TAFS)...

Steady snow will wind down from south to north this afternoon.
Light snow will then be possible at times later this afternoon
into Monday as the low pressure system slowly pulls away. Could
see a little freezing drizzle in the east later this afternoon
into this evening. Additional snow accumulations will be generally
an inch or less this evening into Monday.

Low ceilings will hang on into Monday morning, improving some
Monday afternoon. Visibilities will improve as the steady snow
exits, but will still go down to 2-4 miles at times with the
lingering light snow.

&&

.PREV DISCUSSION... (Issued 1005 AM CDT Sun Apr 15 2018)

UPDATE...

Mainly snow out there this morning, with some sleet in the
southeast. An additional 3 to 5 inches (total daytime
accumulation) is possible in the north, with 1 to 3 inches
farther south...the lighter amounts toward the Illinois border.
Could see some freezing rain mix in late morning into the
afternoon across the south as drier air aloft moves through and
limits ice crystal growth development. Only light icing would be
expected. Steady moderate precip will wind down late afternoon,
with light snow and freezing rain/drizzle possible this evening
into tonight.

MARINE...

Held on to the Gale Warning in the northern marine zone until 1 pm
today, as higher gusts are lingering there. North to northwest
winds will remain gusty into early this week, so issued a Small
Craft Advisory south of Port Washington through 1 pm Tuesday. A
Small Craft Advisory will be issued north of Port Washington after
the Gale Warning expires. There may be a brief lull in the winds
later this evening into early tonight, but then winds will ramp
back up.

Waves will slowly ease today into Monday, especially once the
winds become offshore.

PREV DISCUSSION... (Issued 630 AM CDT Sun Apr 15 2018)

UPDATE...

The feed of moisture and heavier precipitation was pushing north
through southeast Wisconsin. By afternoon this feed will shift
east, with lighter precipitation expected.

Precipitation type is dictated in part due to convective
intensity...trending more snow/sleet in the heavier precip, then
back to a messy mix in the lighter precipitation. Thermal
structure continues to cool, trending more toward light snow later
today and tonight.

AVIATION(12Z TAFS)...

IFR/LIFR conditions will continue, as mixed winter precipitation
impacts southern Wisconsin. Precipitation is heaviest over the
east this morning. This trends the precipitation to snow and
sleet. Lighter precipitation results in a freezing drizzle/light
snow mix. The overall trend eventually is for the precipitation
to be more light snow by tonight.

Winds will remain quite gusty from the northeast, eventually
becoming northwest tonight.

PREV DISCUSSION... (Issued 248 AM CDT Sun Apr 15 2018)

SHORT TERM...

TODAY...Forecast Confidence - Medium.

The Warnings/advisories will continue unchanged.

The biggest forecast challenge with this system continues to be
how the models are handling the warm layer aloft and saturation in
the ice crystal growth zone. Precipitation type is dictated in
part due to convective intensity...trending more snow/sleet in the
heavier precip, then back to a messy mix in the lighter
precipitation. Thermal structure continues to cool, trending more
toward snow. However we loose mid level saturation, with a
shallower dendritic zone by afternoon. Therefore the precipitation
type will continue to be a problem.

The biggest slug of precip will come through through the morning,
especially east, until mid levels dry a bit.

Winds will remain quite strong, although should weaken for a time
until winds become more north, strengthening again.

TONIGHT AND MONDAY...Forecast Confidence - Medium.

700H low pressure slowly exiting the area due to increasing
negative tilt and broadening of the upper trough over the Great
Lakes. Therefore precipitation will continue tonight, with lower
chances hanging on for Monday. Mid-level RH increases a little
with a better chance for ice crystal initiation falling into the
cloud bearing layer. So looking for more light snow and light
accumulations Sunday night into early Monday. Temperature
recovery on Monday will be minimal.

MONDAY NIGHT AND TUESDAY...Forecast Confidence - Medium to High.

A quiet period with some minimal recovery in temperature expected as
short wave ridging affects the area with a weak surface ridge.

LONG TERM...

TUESDAY NIGHT THROUGH SATURDAY - Forecast Confidence...Medium.

The period of quiet weather will be brief as all Medium range
guidance continues to show another deepening low pressure system
affecting southern WI Wednesday morning into possibly Thursday.
The 12Z GFS has trended to the slower ECMWF. The ECMWF is still
somewhat slower, and does not show any precipitation in the
southeast until noon. Precipitation type is questionable due to an
initial 800 mb warm nose of around 4C, with a colder layer below.
The mix of precipitation will trend to rain during the afternoon,
especially southeast. Colder air funnels back into southern WI
late Wednesday into Wednesday night which would result in
changing the mix back to all snow. Mixed precip changing to snow
may result in a Winter Weather Advisory for northern/western
forecast areas depending on timing of the heaviest precip.

Another central Plains low pressure area looks to swing our way over
the weekend, but the models are trending at keeping this to the
south.

No prolonged warming expected.

AVIATION(06Z TAFS)...

IFR conditions will continue overnight tonight, as mixed winter
precipitation impacts the TAF sites. The exact timing of the
various types of precipitation is quite challenging, but overall
a mix of sleet and snow is expected, with occasional periods of
freezing rain mixed in. Snow will become more common with time,
with much of the area seeing mostly snow by tomorrow afternoon and
evening. Winds will remain quite gusty from the northeast tonight
and tomorrow, eventually becoming northwesterly late tomorrow
evening/night.

MARINE...

Northeast Gale force gusts will continue this morning. Winds will
then remain at Small Craft Advisory levels through Monday but
will shift to the north Sunday night as the center of strong low
pressure moves toward Lake Erie.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until midnight CDT tonight for
     WIZ058>060-062>072.

     Winter Storm Warning until midnight CDT tonight for WIZ046-047-
     051-052-056-057.

LM...Small Craft Advisory until 1 PM CDT Tuesday for LMZ643>646.

&&

$$

Update...DDV
Today/Tonight and Aviation/Marine...Hentz
Monday THROUGH Saturday...Hentz



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