A mid to upper level front and low pressure area brought a swath of moderate to heavy snow across Sauk, Columbia, Dodge, northern Jefferson, and northern Dane Counties. Isolated thundersnow was reported.
Every event with a place to put it; 16 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS MKX wrote it up.
A mid to upper level front and low pressure area brought a swath of moderate to heavy snow across Sauk, Columbia, Dodge, northern Jefferson, and northern Dane Counties. Isolated thundersnow was reported. Lighter snow amounts occurred to the north, south, and east of this area. Some schools enacted an early release.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Milwaukee, WI wrote its last area forecast discussion before the first event at Apr 18, 5:30 AM CST, 3 hours 45 minutes earlier.
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
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 from 10 AM this morning to 4 AM CDT
Thursday for WIZ056-062-063-067>069.
Winter Weather Advisory from 1 PM this afternoon to 4 AM CDT
Thursday for WIZ046-047-051-052-057>060-064>066-070>072.
LM...Small Craft Advisory from 1 PM this afternoon to 7 PM CDT
Thursday for LMZ643>646.
&&
Update...Boxell
Today/Tonight and Aviation/Marine...Boxell
Thursday THROUGH Tuesday...99Hazardous Weather Outlook National Weather Service Milwaukee/Sullivan WI 244 AM CDT Wed Apr 18 2018 WIZ046-047-051-052-056>060-062>072-190745- Marquette-Green Lake-Fond Du Lac-Sheboygan-Sauk-Columbia-Dodge- Washington-Ozaukee-Iowa-Dane-Jefferson-Waukesha-Milwaukee- Lafayette-Green-Rock-Walworth-Racine-Kenosha- 244 AM CDT Wed Apr 18 2018 This Hazardous Weather Outlook is for portions of east central Wisconsin, south central Wisconsin and southeast Wisconsin. .DAY ONE...Today and Tonight Precipitation will spread into southern Wisconsin late this morning and exit around or shortly after midnight tonight. The precipitation is expected to be mainly snow and may be heavy at times, impacting the afternoon/evening commute. Snowfall accumulations of 2 to 5 inches are likely with locally higher amounts possible. A Winter Weather Advisory remains in effect for the entire forecast area. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday Some rivers will reach bankfull stage late in the week due to the recent precipitation and melting snow. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed, but snowfall reports will be appreciated today into tonight. LMZ643>646-190745- Sheboygan to Port Washington WI- Port Washington to North Point Light WI- North Point Light to Wind Point WI- Wind Point WI to Winthrop Harbor IL- 244 AM CDT Wed Apr 18 2018 This Hazardous Weather Outlook is for portions of Lake Michigan. .DAY ONE...Today and Tonight Gusty northeast winds today will become northerly by this evening, building high waves. A Small Craft Advisory goes into effect at 1 pm. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday Gusty northerly winds Thursday morning will ease a bit and become northwest during the afternoon hours. Waves will slowly subside late Thursday morning into the afternoon. The Small Craft Advisory is in effect until 7 pm Thursday evening. DDV www.weather.gov/mkx
The national radar mosaic for the moment the first event began.
11 winter weather, 5 winter storm. Local standard time, as filed.
Three to six inches of snow accumulation with the highest totals in the northern portion of the county.
Four to seven inches of snow accumulation in the northern portion of the county with 2 to 3 inches in the southern portion of the county.
Six to eight inches of snow accumulation.
Four to seven inches of snow accumulation in the northern portion of the county with 2 to 4 inches in the southern portion of the county.
Three to six inches of snow accumulation with the highest totals in the northern portion of the county.
Around one inch of snow accumulation.
One to two inches of snow accumulation.
Five to eight inches of snow accumulation.
Six to nine inches of snow accumulation.
Two to five inches of snow accumulation with the highest totals in the northern portion of the county.
Two to five inches of snow accumulation with highest amounts in the southern portion of the county.
Two to four inches of snow accumulation.
Four to six inches of snow accumulation.
Two to four inches of snow accumulation with highest amounts in the southern portion of the county.
One to five inches of snow accumulation with highest amounts in the southern portion of the county.
One to four inches of snow accumulation with highest amounts in the southwest portion of the county.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wisconsin in 2018Every state in 2018This day in weather historyWarnings in Wisconsin, April 2018
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 743679, 743666, 743665, 743667, 743675, 743678, 743677, 743663, 743664, 743676, 743671, 743673, 743674, 743670, 743669, 743672.