Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 181802
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
102 PM CDT Wed Apr 18 2018

.UPDATE...The heavy snow band along the MN/IA border is now
extending ewd into the warned area of Sauk, Iowa, Dane, and
Columbia Counties. The catalyst for this band is 850-700 mb
isentropic lift supported by strong PVA and warm advection at the
jet level. The band will extend farther east and north through the
afternoon but the heaviest amounts will be found in the warned
counties with high end advisory amounts to the east. Much less
snow is expected toward the IL border via the dry slot and toward
central WI which is on the nrn periphery of the storm. The snow
will continue into the evening ending from north to south from 02z
to 05z. Skies will then clear late tnt through Thu. Temps
rebounding into the 40s on Thu.


&&

.AVIATION(18Z TAFS)...A mixture of rain and snow will occur near
the IL and IA border this afternoon into the early evening before
becoming all light snow. Farther north, mostly snow is expected
including moderate to heavy snow at times. Vsbys will fall to
1/4-3/4 miles at times with the snow while Cigs will range from
600-1900 feet. Much lesser impacts toward central WI with this
storm system. Skies will clear from north to south during the late
evening and early morning hours. VFR conditions will continue
through Thu.

&&

.MARINE...A Small Craft Advisory is in effect from this afternoon
until 7 PM Thursday. Brisk nely winds will become nly tonight.
Waves will build to 3 to 6 feet through the afternoon and continue
through Thursday morning. The winds and waves will gradually
subside through Thursday afternoon.


&&

.PREV DISCUSSION... (Issued 630 AM CDT Wed Apr 18 2018)

UPDATE...

Things still appear to be on track at this hour. It still appears
that precipitation will push into southwestern Wisconsin by mid
morning, quickly spreading across the entirety of the forecast
area by early afternoon.

AVIATION(12Z TAFS)...

Snow will overspread the terminals later today, with a period of
moderate and perhaps even heavy snow possible during the mid to
late afternoon hours. Visibility should fall to LIFR within the
heaviest bands, with widespread IFR ceilings and visibility
outside of the heavier bands. Winds will initially be from the
northeast, and will become more northerly by evening, then
eventually northwest late tonight. Gusts will pick up as well as
winds become northwesterly.

Snow will end late this evening, with skies scattering out to VFR
overnight.

PREV DISCUSSION... (Issued 300 AM CDT Wed Apr 18 2018)

SHORT TERM...

Today and Tonight...Forecast confidence medium to high...

A strong storm system will bring a quick hitting bout of snow to
the region later this morning through the afternoon hours. The
latest forecast data suggests a slightly slower and more southerly
track to the axis of heaviest snowfall. Snow should overspread the
area from the southwest mid to late morning, reaching a line from
roughly the Dells to Janesville by noon. The snow will then make
quick progress north, overspreading the entire forecast area by
the mid afternoon hours. While the bulk of the precipitation is
expected to fall as snow, a brief period of wintry mix is possible
along the very leading edge of the area of snow. In addition, a
considerable amount of lightning has been noted across western
Iowa this morning, and would not be at all surprised to get
reports of thundersnow, especially along the leading edge of the
precipitation.

One or more bands of fairly intense snow are expected, especially
during the afternoon and early evening hours, when snowfall rates
along the US 18 and I-94 corridors could be greater than 1" per
hour. This is expected to cause impacts to travel, including
during the afternoon/evening commute.

Snow will continue into this evening, before ending late tonight.
Total snow amounts are expected to range from 4-6 inches along and
south of I-94, to 2-4 inches north. The lowest amounts are
expected to fall across Fond du Lac and Sheboygan Counties.

The Winter Weather Advisory will remain in place for the entire
forecast area. We did adjust the start time for the portion of the
advisory east of I-90 from 10 AM to 1 PM to account for the slower
progression of the snow.

LONG TERM...

Thursday through Monday...Forecast confidence is high:

High pressure centered just to the west of southern Wisconsin
Thursday will slide over the area Friday, continuing to move
slowly eastward over the weekend into early next week. This high
will bring dry weather and plenty of sunshine to the forecast area
through this period. Temperatures will finally warm back to
around normal by the weekend...and might even be a couple degrees
above normal by Monday!

Tuesday...Forecast confidence is medium:

Models show a low pressure and an associated cold front to move
through around Tuesday. This may bring some showers to southern
Wisconsin. Though there`s decent timing agreement among models for
several days out, models differ on moisture/strength/placement of
this system, so just kept precip chances on the low end for now.
It does look like the milder temps will continue Tuesday ahead of
the cold front.

AVIATION(09Z TAF Update)...

Snow will overspread the terminals this afternoon, with periods of
moderate to heavy snow possible during the mid to late afternoon
hours. A few rumbles of thunder are also possible. Visibility is
likely to drop to LIFR at times within the heavier bands. Outside
of the heaviest bands, widespread IFR cigs and vis are likely to
be observed.

Snow will end late this evening or overnight, with skies
scattering out to VFR.

Winds will be from the east-northeast today, becoming more
northerly late tonight. Gusts between 20 and 25 knots are expected
this evening and tonight.

MARINE...

A Small Craft Advisory will be in effect from this afternoon
through early Thursday evening.

East to northeast winds will result in building waves today across
the nearshore waters, with waves building further this evening as
winds increase from the north. Gusts may approach gale force at
times this evening, but should mostly remain just below.

Breezy northwest winds will continue on Thursday, before
decreasing Thursday evening. After that, a period of fairly quiet
weather is expected.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 1 AM CDT Thursday for WIZ067>069.

     Winter Weather Advisory until 1 AM CDT Thursday for WIZ046-047-
     051-052-058>060-064>066-070>072.

     Winter Storm Warning until 1 AM CDT Thursday for WIZ056-057-062-
     063.

LM...Small Craft Advisory until 7 PM CDT Thursday for LMZ643>646.

&&

$$

Update...Gehring
Today/Tonight and Aviation/Marine...Boxell
Thursday THROUGH Tuesday...DDV


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