Wisconsin Lake Ice In Dates and Freeze Over Records

Q: How do I know whether the ice is safe?

Contact your state agency and look at the water yourself. Every figure here is the day a lake closed over in a past winter. Ice strength varies across a single lake on a single day with depth, current, springs and snow cover, and a lake that has just closed over is at its most deceptive: it looks like a solid surface and it is a few days of new ice.

Q: Who publishes this winter's Wisconsin ice in dates?

Wisconsin State Climatology Office lake ice tables. The State Climatology Office at UW Madison publishes freeze-over date, thaw date and days of ice cover for the Madison lakes and updates them every winter. They hold the current winter; this page holds the long one, and the two will not always agree because the office computes its own comparison periods.

Q: Is ice in getting later in Wisconsin?

In this data, yes on 8 of the 8 Wisconsin records long enough to state a century trend. The largest is Big Green Lake. Those figures are least squares lines fitted to the observations, the same simple description the ice phenology literature uses. They describe what the record did. They are not projections, and any single lake can swing three or four weeks between consecutive winters.

Q: Do Wisconsin lakes ever fail to freeze?

Yes. 4 of the 17 Wisconsin water bodies here have winters on record in which they never closed over, 10 winters in total. Those winters are kept in the data rather than dropped, because a winter with no ice is an observation, and treating it as missing would bias every average on this page toward an earlier freeze.

Q: How does ice in compare with ice out on the same Wisconsin lakes?

They are the two ends of one season and they have moved in opposite directions. Wisconsin lakes appear in both halves of this dataset, and where a lake carries a long enough record on both, the freeze has been arriving later while the thaw has been arriving earlier. The ice-out page for Wisconsin carries the thaw half of the same records, lake by lake, from the same source.

Typical ice in on Lake Monona

December 15

That is the median across 166 recorded winters from 1851 to 2018, the deepest freeze record in Wisconsin. Across the 17 Wisconsin water bodies on this page the typical closing runs from November 15 on Maple Lake to January 9 on Lake Superior at Madeline Island. Each of those is a median from a record of past winters, not a forecast or an observation of any lake now.

December 24

Lake Monona across its last 30 recorded winters

55 days

Between the earliest and latest typical freeze in the state

8 of 8

Records long enough to state a century trend that show a later freeze

10

Winters with no freeze at all, on 4 of these water bodies

Every Wisconsin water body, in the order they close

Each bar runs from that water body's earliest recorded closing to its latest, across the whole Wisconsin record. The solid dot is the median over every recorded winter and the ring is the median over the most recent 30. The scale starts near the earliest date in the set rather than at January 1, because these are dates a few weeks apart.

Where this winter’s dates come from

The State Climatology Office at UW Madison publishes freeze-over date, thaw date and days of ice cover for the Madison lakes and updates them every winter. They hold the current winter; this page holds the long one, and the two will not always agree because the office computes its own comparison periods.

Wisconsin State Climatology Office lake ice tables

Today against the record

How this point in the season has usually played out

Where today sits in the Lake Monona record

Today is earlier in the ice season than any closing in this record. The earliest Lake Monona ever closed over in 166 recorded winters was November 23, in 1857, which is 35 days from now on this year’s calendar.

The median across the whole record is December 15, which is 57 days from now on this year’s calendar. The record itself ends in 2018, so this is a comparison against past winters and not a statement about the current one.

This counts recorded winters, not this one; the current winter comes from the agency linked above.

Lake Monona, recorded closings by winter

1979 to 2018, 40 winters, median Dec 15

Taller means later in the season. The darker columns are the more recent half of the window. The dashed line is the median across the whole record, not just this window, and the vertical scale starts near the earliest date on the chart rather than at January 1 so that a three week shift stays visible. The source ships the most recent 40 observations here, so this window is the tail of a record that begins in 1851. 8 of these winters carry more than one closing, because the lake shut, a thaw opened it and it shut again, and the source keeps both rather than choosing.

Water body by water body

The deepest Wisconsin freeze records

Ordered by how much record is behind them. The median is across every recorded winter; the second figure is across the most recent 30, which is the fairer thing to compare against a lake you know today.

Names are reproduced exactly as the source database records them, which is often a shortened form: a lake filed as “Detroit” or “Otsego” is Detroit Lake or Otsego Lake to everyone who lives on it. The names stay as recorded, because United States lakes split unpredictably between “Lake X” and “X Lake”; the subtitle on each card carries the water body type and the state.

Lake Monona

Lake in Wisconsin · 166 recorded winters, 1851 to 2018

Dec 15

typical ice in

Dec 24

last 30 recorded winters

Nov 23

earliest, 1857

Jan 30

latest, 1932

Across the whole record the closing date has moved 8 days later per century across the record.

Its ice out has moved 12 days earlier per century across the record, so adding the two lines together this lake’s ice season is about 20 days shorter per century.

Mean closing date per decade. Only decades with four or more observations appear, and the scale starts near the shortest bar rather than at January 1 so that small differences stay visible rather than collapsing into one length.

Lake Mendota

Lake in Wisconsin · 165 recorded winters, 1853 to 2018

Dec 20

typical ice in

Dec 27

last 30 recorded winters

Nov 24

earliest, 1880

Jan 30

latest, 1932

Across the whole record the closing date has moved 8 days later per century across the record.

Its ice out has moved 9 days earlier per century across the record, so adding the two lines together this lake’s ice season is about 17 days shorter per century.

Mean closing date per decade. Only decades with four or more observations appear, and the scale starts near the shortest bar rather than at January 1 so that small differences stay visible rather than collapsing into one length.

Lake Superior at Bayfield

Lake in Wisconsin · 153 recorded winters, 1858 to 20194 winters open

Jan 1

typical ice in

Jan 13

last 30 recorded winters

Dec 2

earliest, 1880

Mar 10

latest, 2002

Across the whole record the closing date has moved 15 days later per century across the record.

Its ice out has moved 16 days earlier per century across the record, so adding the two lines together this lake’s ice season is about 32 days shorter per century.

4 winters on record it never closed over at all, most recently the one ending in 2017. Those winters are counted separately from the 153 dates above.

Mean closing date per decade. Only decades with four or more observations appear, and the scale starts near the shortest bar rather than at January 1 so that small differences stay visible rather than collapsing into one length.

Lake Geneva

Lake in Wisconsin · 151 recorded winters, 1863 to 20194 winters open

Jan 2

typical ice in

Jan 12

last 30 recorded winters

Nov 24

earliest, 1880

Mar 11

latest, 1932

Across the whole record the closing date has moved 11 days later per century across the record.

Its ice out has moved 5 days earlier per century across the record, so adding the two lines together this lake’s ice season is about 17 days shorter per century.

4 winters on record it never closed over at all, most recently the one ending in 2017. Those winters are counted separately from the 151 dates above.

Mean closing date per decade. Only decades with four or more observations appear, and the scale starts near the shortest bar rather than at January 1 so that small differences stay visible rather than collapsing into one length.

A wall of shelf ice rising above a lake surface strewn with broken plates of new ice and patches of dark open water, under a blue sky with high cloud — Shelf ice standing above a field of broken new plates, with open water still showing between them. This is the state a lake is in for days or weeks before anybody writes a closing date against it, and it is why two observers standing on the same shore can pick two different days. “Ice along Lake Superior” — National Park Service, Pictured Rocks National Lakeshore — Public domain

Every record

All 17 Wisconsin water bodies with a freeze record

Water body	Record	Typical ice in	Last 30 winters	Earliest	Latest	Change per century	Winters open
Maple Lake	1952 to 2004 (53)	Nov 15	Nov 12	Oct 31 1988	Dec 13 1990	record too short	0
Mystery Lake	1962 to 2018 (47)	Nov 17	Nov 20	Nov 4 1991	Dec 13 1998	record too short	0
Spruce Lake	1962 to 2018 (51)	Nov 19	Nov 23	Oct 25 1976	Dec 13 1998	record too short	0
Lake Shishebogama	1958 to 2001 (43)	Nov 22	Nov 22	Nov 8 1991	Dec 14 1998	record too short	0
Lake Escanaba	1955 to 2018 (60)	Nov 25	Nov 28	Nov 6 1973	Dec 28 2015	record too short	0
Lake Nebish	1959 to 2018 (50)	Nov 27	Nov 29	Nov 8 1991	Dec 28 2001	record too short	0
Lake Wingra	1877 to 2019 (82)	Nov 30	Dec 4	Nov 2 1913	Dec 30 2015	+6.6 days	0
Shell Lake	1905 to 2019 (112)	Dec 2	Dec 5	Nov 2 1915	Dec 25 2001	+7.4 days	0
Big Muskellunge Lake	1947 to 2017 (51)	Dec 3	Dec 4	Nov 12 1995	Dec 27 2015	record too short	0
Lake Kegonsa	1905 to 2006 (68)	Dec 9	Dec 12	Nov 15 1959	Dec 28 1927	+1.3 days	0
Lake Monona	1851 to 2018 (166)	Dec 15	Dec 24	Nov 23 1857	Jan 30 1932	+7.8 days	0
Devils Lake	1941 to 2004 (55)	Dec 18	Dec 23	Nov 30 1959	Jan 27 2003	record too short	0
Lake Mendota	1853 to 2018 (165)	Dec 20	Dec 27	Nov 24 1880	Jan 30 1932	+8.3 days	0
Lake Superior at Bayfield	1858 to 2019 (153)	Jan 1	Jan 13	Dec 2 1880	Mar 10 2002	+15.4 days	4
Lake Geneva	1863 to 2019 (151)	Jan 2	Jan 12	Nov 24 1880	Mar 11 1932	+11.1 days	4
Big Green Lake	1940 to 2020 (80)	Jan 9	Jan 14	Dec 12 1995	Feb 24 2006	+16.9 days	1
Lake Superior at Madeline Island	1964 to 2007 (43)	Jan 9	Jan 11	Dec 11 1976	Mar 11 2002	record too short	1

Dates are day of year, rendered on a common non leap calendar so the same stored value always reads the same way. Freeze dates are stored on a winter axis, where a January closing sorts after a December one instead of jumping back to the start of the year; the labels above are ordinary calendar dates. “Change per century” is a least squares line through the observations, shown only where a record spans 80 years or more, because a century figure extrapolated from a 40 year window describes the decades that happened to be sampled rather than the lake. “Winters open” counts the winters the source marks as never closing over, which are observations rather than gaps and are not included in the record counts.

Both ends of the season

How much shorter the Wisconsin ice season has got

8 Wisconsin water bodies carry a least squares slope on both the freeze and the thaw, which is the only way to see the season from both ends at once. Adding one lake’s own freeze line to its own thaw line, the widest here is Lake Superior at Bayfield at 31.6 days shorter per century.

That is addition on two numbers the source data already publishes for that lake: a description of what one lake’s own record did across the years somebody was watching it, not a model and not a projection of what the next decade will do.

Freeze arriving later
Thaw arriving earlier

Each bar is one Wisconsin lake's own freeze line added to its own thaw line, both fitted by least squares to that lake's observations and both already published in the source data. Only records spanning 80 years or more on both variables appear, which is why not every water body in the table above is here.

Reading the record

What the Wisconsin freeze record shows

Of the 8 Wisconsin freeze records long enough to state a century trend, 8 show the closing date arriving later. Those are least squares lines fitted to observations, the same simple description the ice phenology literature uses. They describe what each record did. Any single lake can swing three or four weeks between consecutive winters, and several here have.

A typical ice in date is a median drawn from a record: the middle of a distribution whose ends, on these Wisconsin records, sit 90 days apart on Lake Superior at Madeline Island alone. It describes past winters, not the current one.

Lake Superior at Bayfield did not close over at all in 4 winters on record, which is 3 percent of the winters in its span, and the eight most recent of those ended in 1998, 2012, 2016, 2017. The source records those winters rather than leaving them blank, and this page keeps them, because dropping them and averaging only the winters the water did close would bias the record toward an earlier freeze. In Wisconsin that is the single most important thing the freeze record has to say.

The Wisconsin State Climatology Office treats the freezing date as the first date on which the majority of the lake surface is estimated to be frozen, and says on the same page that no reliable information about ice thickness is available for these lakes. Two of the Wisconsin series here use a working definition instead of an observed one: at Bayfield the freeze is dated by the last boat to leave the harbour, and at Madeline Island by the ferry route closing.

The freeze date somebody could actually see. On open water the size of Lake Superior nobody can watch a whole bay close over, so the Bayfield record uses the thing a harbour town could see from the dock: the last boat out in the winter and the first boat out in the spring. The database carries that definition in its own notes, and it is why the Bayfield series exists at all when the lake itself is too big to call.

Two lakes in one city, five days apart. Lake Monona and Lake Mendota sit either side of the Wisconsin isthmus and have been watched since the early 1850s. Monona is the smaller and shallower of the two and typically closes about five days before Mendota does, every winter, which is the clearest illustration in the whole dataset that depth and area set the freeze date rather than latitude.

Satellite view of Lake Superior in mid December with the surrounding land under snow, the open lake dark, and pale new ice showing in the shallow western bays — Lake Superior on December 15, with the first ice of that winter forming in the shallow western bays while the deep middle stays open. Depth is what sets a freeze date: a shallow bay gives up its summer heat in weeks and the deep middle can take all winter or never manage it. “Lake Superior (MODIS 2018-12-20)” — MODIS Land Rapid Response Team, NASA GSFC — Public domain

Provenance

Where these Wisconsin numbers came from

The observations

1,430 recorded closings across 17 Wisconsin water bodies, from 1851 to 2020. Only records with 40 or more usable observations are included, and every derived figure is computed from them.

Benson, B., Magnuson, J. and Sharma, S. (2000). Global Lake and River Ice Phenology Database. (G01377, Version 1). Boulder, Colorado USA. National Snow and Ice Data Center. https://doi.org/10.7265/N5W66HP8 Accessed 2026-08-24.

Lake Superior at Bayfield has the largest freeze shift of any Wisconsin record here, and its last four winters with no closing at all are 1998, 2012, 2016 and 2017.

Common questions

Wisconsin lake ice in FAQ

When do lakes usually freeze over in Wisconsin?

It depends on the lake, so this page gives a figure for each one instead of a single state number. Lake Monona has the deepest record in Wisconsin at 166 recorded winters and typically closed over around December 15, or December 24 across its most recent 30 recorded winters. Across the 17 Wisconsin water bodies here the typical date runs from November 15 on Maple Lake to January 9 on Lake Superior at Madeline Island. Every one of those is a median drawn from past winters and none of them describes this one.

How do I know whether the ice is safe?

Who publishes this winter's Wisconsin ice in dates?

What exactly counts as ice in on a Wisconsin lake?

The Wisconsin State Climatology Office treats the freezing date as the first date on which the majority of the lake surface is estimated to be frozen, and says on the same page that no reliable information about ice thickness is available for these lakes. Two of the Wisconsin series here use a working definition instead of an observed one: at Bayfield the freeze is dated by the last boat to leave the harbour, and at Madeline Island by the ferry route closing. That matters most when you compare two lakes against each other and least when you compare one lake against its own past, which is what every figure on this page is built for.

How far back do Wisconsin freeze records go?

The oldest freeze observation in Wisconsin in this dataset is from 1851 and the most recent is from 2020. Across the state this page covers 17 water bodies with at least 40 recorded winters each, 7 of which span a century or more, and 1,430 individual freeze dates in total. Almost none of it was collected for science. It was kept by field stations, fisheries staff, harbour masters, newspapers and individuals for practical reasons, and became a climate record afterwards.

Is ice in getting later in Wisconsin?

Do Wisconsin lakes ever fail to freeze?

How does ice in compare with ice out on the same Wisconsin lakes?

Rounded plates of new pancake ice packed across a lake surface with steam fog rising off the open water beyond and frost covered bare branches overhanging from above — Pancake ice on Big Green Lake in Wisconsin, photographed on December 27. Big Green typically closes over about a fortnight later, and it is the second widest closing season in this whole dataset. Plates of new ice grinding against each other and rounding their own edges is what the days before a freeze date look like. “Ice on Green Lake” by Wideshpan6, CC BY-SA 4.0

The other end of the season

Ice in, ice out, and the rest of the Wisconsin winter

Wisconsin ice inWhen 17 Wisconsin water bodies have typically closed over, from 1,430 recorded winters. You are on it.

Wisconsin ice outThe spring half of the same records, lake by lake, from the same source. Together they are the length of the Wisconsin ice season.

Every state with a freeze recordThe national picture, the ice season closing from both ends, and every state with a freeze record.Wisconsin winter outlookWhat NOAA expects from the season that puts the ice on in the first place.Wisconsin first snowThe other autumn threshold, on the same calendar and from a different federal record.

More Midwest states with a lake freeze record

Ice in dates are historical observations compiled by the National Snow and Ice Data Center. They describe past winters only: a median freeze date is a record of winters that have already happened, and says nothing about the ice on any lake today. For current ice and for anything involving going out on it, contact Wisconsin DNR. National picture: every state with a lake freeze record → The thaw half: Wisconsin lake ice out dates.
Hero image: “Ice on Green Lake” by Wideshpan6, CC BY-SA 4.0