Madison Freeze-Thaw, Salt and Lake Chloride Data for Pavement
Last reviewed 2026-07-25. Journalists, researchers, and community groups are welcome to cite any figure on this page with attribution and a link.
This page collects the figures behind the rest of the site, each with its source. Climate values are NOAA's 1991-2020 normals for the Dane County Regional Airport station (USW00014837) on the city's northeast side. NOAA publishes its day counts in tenths; a freeze-thaw day here is one that dips to 32 or below overnight yet climbs above freezing by afternoon, computed as freezing nights minus days that stay frozen from start to finish.
Salt and chloride figures come from Public Health Madison and Dane County's 2022 road salt report, the sealer rule from the Dane County Code of Ordinances, and population and housing counts from Census Bureau QuickFacts and the 2019-2023 American Community Survey. Where the rest of the site rounds a value, the tables below show it as published.
87 days
freeze-thaw days a year at Dane County Regional Airport
NOAA 1991-2020 normals
50.9 in
normal annual snowfall at the airport station
NOAA 1991-2020 normals
129 mg/L
chloride in Lake Wingra in 2022, highest of the five lakes
Public Health Madison & Dane County
0.1%
PAH limit by weight for any pavement sealer used in Dane County
Dane County Code ch. 80
Freeze-thaw days and temperatures by month
March is the hardest month on pavement at the airport station, with about 19 freeze-thaw days, followed by November at about 15. June, July and August record none. The monthly counts add up to the annual 87.2, which is the 148.5 nights at or below freezing minus the 61.3 days that stay frozen all day.
| Month | Nights at or below 32F | Days with high at or below 32F | Freeze-thaw days | Normal high / low (F) |
|---|---|---|---|---|
| January | 29.9 | 20.4 | 9.5 | 26.4 / 11.1 |
| February | 26.3 | 14.4 | 11.9 | 31.1 / 15.1 |
| March | 24.0 | 4.9 | 19.1 | 43.1 / 24.8 |
| April | 10.3 | 0.3 | 10.0 | 57.3 / 35.8 |
| May | 1.4 | 0.0 | 1.4 | 68.4 / 46.1 |
| June | 0.0 | 0.0 | 0.0 | 77.9 / 56.1 |
| July | 0.0 | 0.0 | 0.0 | 81.6 / 61.0 |
| August | 0.0 | 0.0 | 0.0 | 79.4 / 59.0 |
| September | 0.5 | 0.0 | 0.5 | 71.8 / 50.2 |
| October | 7.9 | trace | 7.9 | 58.9 / 38.8 |
| November | 19.6 | 4.4 | 15.2 | 44.1 / 28.2 |
| December | 28.6 | 16.9 | 11.7 | 30.2 / 15.9 |
| Year | 148.5 | 61.3 | 87.2 | annual mean 46.5 |
Source: monthly normals for station USW00014837 (NOAA, 1991-2020). October's count of days that stay at or below freezing is published as a nonzero value too small to show, so it is listed as a trace.
Frost dates, snow and rain
The sealing season sits well inside the freeze-free window. A coat needs about a day at 50 degrees or more with temperatures still rising, and normal lows clear 50 only from June through September, so the median frost dates mark the outer edges of the season rather than its working weeks.
| Measure | Value |
|---|---|
| Median last spring freeze (32F) | May 2 |
| Median first fall freeze (32F) | October 5 |
| Median freeze-free season (32F) | 152 days |
| Median last and first 28F nights | April 22 and October 17 |
| Normal annual snowfall | 50.9 in |
| Normal December to February snowfall | 37.0 in |
| Days a year with 1 inch or more of new snow | 14.7 |
| Normal annual precipitation | 34.48 in |
| Days a year with 1 inch or more of precipitation | 7.4 |
| Nights a year at or below 0F | 15.3 |
NOAA 1991-2020 annual and seasonal normals for Dane County Regional Airport. Freeze dates are the 50 percent probability dates.
Salt and chloride in the lakes and wells
Naturally occurring chloride is under 10 mg/L in most Wisconsin water, according to Wisconsin Salt Wise, and the state's chronic toxicity criterion cited in the county report is 395 mg/L. All five lakes measured in 2022 sat several times above that natural level. City road salt use has fallen since 2015, which the report credits partly to mild winters and partly to fewer routes during virtual schooling, even though per-mile application rates rose.
| Water body or measure | Value | Year |
|---|---|---|
| Lake Wingra chloride | 129.0 mg/L | 2022 |
| Lake Monona chloride | 75.9 mg/L | 2022 |
| Lake Waubesa chloride | 75.7 mg/L | 2022 |
| Lake Kegonsa chloride | 71.6 mg/L | 2022 |
| Lake Mendota chloride | 57.7 mg/L | 2022 |
| Yahara River chloride | 53.0 mg/L | 2022 |
| Deeply cased city wells, chloride | 4 mg/L, then 18 mg/L | 1982, then 2022 |
| City wells with short casings, chloride | 5 mg/L, then 46 mg/L | 1982, then 2022 |
| City of Madison road salt use | 16,351 tons, then 6,124 tons | 2013, then 2022 |
Public Health Madison and Dane County, Road Salt Report 2022 (updated April 2023). The report notes that all well values remain below EPA limits.
People and housing in Madison and four nearby cities
The newer the housing, the younger the typical driveway. Madison's median home dates to 1980 and Middleton's to 1986, while Verona, the fastest-growing of the five since 2020, also has the newest housing, with a median build year of 2002.
| City | 2020 census | 2025 estimate | Housing units | Median year built |
|---|---|---|---|---|
| Madison | 269,840 | 286,233 | 133,530 | 1980 |
| Middleton | 21,827 | 23,115 | 10,793 | 1986 |
| Fitchburg | 29,609 | 34,615 | 15,929 | 1996 |
| Sun Prairie | 35,967 | 39,227 | 16,195 | 1999 |
| Verona | 14,030 | 16,821 | 6,651 | 2002 |
Population: Census Bureau QuickFacts (April 1, 2020 census and July 1, 2025 estimates). Housing units and median year built: 2019-2023 American Community Survey 5-year estimates as published by Point2Homes.
Rules that touch a driveway
- Dane County Code ch. 80: no application, sale or display of coal tar or high-PAH (over 0.1 percent by weight) sealers anywhere in the county; each day an illegal coating remains is a separate offense.
- Madison: alternate side parking November 15 to March 15, 1 to 7 a.m. (in the Snow Emergency Zone only during declared emergencies); sidewalks cleared by noon the day after snow stops (MGO 10.28); street terrace permit for residential driveway aprons.
- Middleton: alternate side parking November 15 to March 15, 1 to 7 a.m.; sidewalks cleared within 24 hours (Ordinance 8.07); street opening permit for right-of-way work that disturbs pavement.
- Fitchburg: alternate side parking November 15 to March 15, 1 to 7 a.m.; sidewalks cleared by 6 p.m. the day after (Sec. 27-114); one right-of-way permit for driveway, occupancy and excavation work.
- Sun Prairie: snow route parking ban midnight to 7 a.m., December 1 to March 31; Engineering Department driveway permit for replaced, modified or new driveways.
- Verona: parking restricted 1 to 6 a.m., November 20 to April 1, alternating sides (Sec. 10-1-29); sidewalks cleared within 24 hours (Sec. 6-2-7).
Sources & Methodology
Every figure above was taken from the primary sources below (accessed 2026-07-25). Where a number is derived (arithmetic on published figures) or covers a broader period or area, the text says so.
- Dane County Regional Airport annual normals (NOAA NCEI, 1991-2020) — Station name; annual nights at or below 32F (148.5) and days at or below 32F (61.3); snowfall 50.9 in; freeze dates May 2 and October 5; 152-day season; precipitation and snow day counts.
- Monthly temperature normals for station USW00014837 (NOAA NCEI) — Monthly freezing-night and freezing-day counts and normal highs and lows used in the monthly table.
- Public Health Madison and Dane County, Road Salt Report 2022 — Lake and Yahara River chloride for 2022, well chloride 1982 and 2022, city road salt use 2013 and 2022.
- Dane County Code of Ordinances, Chapter 80 — Coal tar and high PAH (over 0.1 percent) sealant definitions, prohibitions, countywide applicability, enforcement and daily-offense clause.
- Wisconsin Salt Wise, salt impacts overview — Natural chloride under 10 mg/L in most Wisconsin water; 395 mg/L toxicity level.
- U.S. Census Bureau QuickFacts, Madison city, Wisconsin — 2020 census population, 2025 estimate and owner-occupancy for Madison; the other cities use their own QuickFacts pages.
- Point2Homes, Madison WI demographics (2019-2023 ACS) — Housing units, year-built distribution and median year built for Madison; matching pages give the four suburbs.
- City of Madison, Winter Parking Rules — Alternate side parking November 15 to March 15, 1 to 7 a.m., and the Snow Emergency Zone exception.
- Verona, Snow and Ice Ordinances — Winter parking November 20 to April 1, 1 to 6 a.m. (Sec. 10-1-29), and the 24-hour sidewalk rule (Sec. 6-2-7).
Seen enough numbers? Ask independent Madison-area crews for a written quote built on them.
Quick Answers
What counts as a freeze-thaw day in these tables?
Start with every day whose low hits 32 degrees or colder, then take away the days that stay at or below freezing all afternoon. What is left are the days that swing across freezing, melting by afternoon and refreezing at night or the reverse. With NOAA's 1991-2020 airport normals that is 148.5 minus 61.3, about 87 days a year.
Why use the airport station instead of a downtown thermometer?
Dane County Regional Airport is the NOAA station with a full set of 1991-2020 normals for the area, including the day counts and freeze-date probabilities used here. A single year's readings swing widely, and 30-year normals describe what a typical year looks like, which is what a maintenance schedule needs. Local conditions, such as a lakeside lot or a shaded drive, can run a little warmer or colder.
Are the lake chloride numbers rising or falling?
Rising, even as city salt use has fallen. The 2022 report notes an increase of 17 percent in Lake Wingra and about 7 percent in the other Yahara lakes over the period it compares, while total city road salt use has dropped since 2015. Chloride does not break down once it reaches water, so salt from past winters stays in the lakes, and private applicators on lots and driveways keep adding to it.
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