Oconomowoc, Wisconsin climate: Normal weather by month, frost dates and records
Oconomowoc's normal year runs from 11°F January nights to 82°F July afternoons, with 36.8 inches of precipitation and 40 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 8.4°C, January lows of −12°C, July highs of 28°C, 935 mm of precipitation a year.
- NOAA stationOconomowoc Wastewater Treatment Plant
- Station IDUSC00476200
- Location43.10°N 88.50°W
- Elevation858 ft (262 m)
- From the centerunder 1 mile
- Population20,002
On October 14, the normal high in Oconomowoc is 62°F and the normal low 40°F, and the chance of measurable rain or snow is 35%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Oconomowoc.
- Jan 28° 11°
- Feb 32° 14°
- Mar 44° 25°
- Apr 56° 36°
- May 69° 47°
- Jun 78° 57°
- Jul 82° 61°
- Aug 81° 60°
- Sep 74° 52°
- Oct 61° 40°
- Nov 46° 29°
- Dec 34° 18°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like in Oconomowoc each month?
July is the warmest month, with normal highs of 82°F; January the coldest, with normal lows of 11°F. The most precipitation falls in June (4.86 in), the least in February (1.61 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 28°F | 11°F | 19.6°F | 1.65 | 11.1 | 11 | <1 | 30 | 9 h 20 min |
| February | 32°F | 14°F | 23.0°F | 1.61 | 9.8 | 10 | <1 | 27 | 10 h 30 min |
| March | 44°F | 25°F | 34.2°F | 2.10 | 4.8 | 10 | <1 | 24 | 11 h 50 min |
| April | 56°F | 36°F | 46.1°F | 3.86 | 2.0 | 12 | <1 | 10 | 13 h 20 min |
| May | 69°F | 47°F | 57.9°F | 4.14 | 0.2 | 13 | <1 | 1 | 14 h 40 min |
| June | 78°F | 57°F | 67.7°F | 4.86 | 0.0 | 12 | 2 | <1 | 15 h 20 min |
| July | 82°F | 61°F | 71.8°F | 4.12 | 0.0 | 10 | 3 | <1 | 15 h 10 min |
| August | 81°F | 60°F | 70.2°F | 4.17 | 0.0 | 10 | 2 | <1 | 14 h |
| September | 74°F | 52°F | 62.7°F | 3.39 | 0.0 | 10 | 1 | <1 | 12 h 30 min |
| October | 61°F | 40°F | 50.3°F | 2.83 | 0.1 | 11 | <1 | 7 | 11 h 10 min |
| November | 46°F | 29°F | 37.3°F | 2.21 | 1.4 | 10 | <1 | 20 | 9 h 50 min |
| December | 34°F | 18°F | 25.9°F | 1.87 | 10.2 | 11 | <1 | 28 | 9 h |
| Year (annual) | 57°F | 37°F | 47.2°F | 36.81 | 39.6 | 129 | 7 | 146 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | −2°C | −12°C | −6.9°C | 42 mm | 28 cm |
| February | 0°C | −10°C | −5.0°C | 41 mm | 25 cm |
| March | 7°C | −4°C | 1.2°C | 53 mm | 12 cm |
| April | 14°C | 2°C | 7.8°C | 98 mm | 5 cm |
| May | 20°C | 8°C | 14.4°C | 105 mm | 1 cm |
| June | 26°C | 14°C | 19.8°C | 123 mm | 0 cm |
| July | 28°C | 16°C | 22.1°C | 105 mm | 0 cm |
| August | 27°C | 15°C | 21.2°C | 106 mm | 0 cm |
| September | 23°C | 11°C | 17.1°C | 86 mm | 0 cm |
| October | 16°C | 4°C | 10.2°C | 72 mm | 0 cm |
| November | 8°C | −2°C | 2.9°C | 56 mm | 4 cm |
| December | 1°C | −8°C | −3.4°C | 47 mm | 26 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00476200; annual normals. Wet days: 0.01 inch or more; 90°F days and freezing nights: NOAA's day counts. Daylight: sunrise to sunset on the 15th, computed from the latitude.
When is the best weather to visit Oconomowoc?
Normal highs sit between 65°F and 85°F in May, June, July, August and September. Of those, September has the fewest days with rain (10).
That is a measurement, not a recommendation: it counts the months whose normal afternoon high sits between 65°F and 85°F, where a light layer is enough by day.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00476200.
When is the last frost in Oconomowoc?
In Oconomowoc, the last spring frost (32°F) comes after April 30 in half of years and after May 17 in one year in ten; the first autumn frost comes before October 12 in half of years and before September 29 in one year in ten.
Frost-free in half of yearsFrost in 1 to 9 years out of 10Frost most years
- Last spring frost, half of years after
- April 301 year in 10 after May 17; 9 in 10 after April 16
- First autumn frost, half of years before
- October 121 year in 10 before September 29; 9 in 10 before October 27
NOAA puts the median frost-free season at 164 days, and the season without a hard freeze (28°F) at 186 days.
A hard freeze (28°F) comes after April 19 in half of springs and before October 24 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Oconomowoc in zone 5b in ZIP code 53066. By the map's own method, the average of each year's coldest night over 1991-2020, Oconomowoc's NOAA station is in zone 5b: the coldest night of a typical year reaches −15°F (26 complete years).
Frost dates for every NOAA station in Wisconsin · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00476200; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; the station zone: ACIS daily lows, 1991-2020. A 10% date means one year in ten has a frost after it in spring or before it in autumn.
How hot and how cold does it get in Oconomowoc?
In a normal year in Oconomowoc, 7 days a year reach 90°F, 146 nights fall to 32°F or colder and 129 days bring measurable precipitation.
- Days at 90°F or more
- 7a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 146a normal year
- Days that stay below freezing
- 58high of 32°F or less
- Days with 0.01 inch of precipitation
- 129a normal year
- Days with 1 inch of snow or more
- 13a normal year
The highest temperature in this station's record (since 1893) is 103°F, on July 6, 2012; the lowest is −33°F, on January 30, 1951.
The wettest calendar year on that record is 2018, with 47.24 in; the snowiest season is 2007–08, with 85.0 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00476200; records: ACIS (NOAA Regional Climate Centers), station USC00476200. Records use complete months only; a month missing more than three days is left out.
How sunny is Oconomowoc?
Over a year 72% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Oconomowoc, 3.8 kWh per square metre a day. July is the sunniest month (80%) and December the cloudiest (59%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 63% | 1.6 |
| February | 70% | 2.7 |
| March | 70% | 3.7 |
| April | 68% | 4.6 |
| May | 71% | 5.5 |
| June | 76% | 6.1 |
| July | 80% | 6.3 |
| August | 78% | 5.3 |
| September | 77% | 4.2 |
| October | 68% | 2.7 |
| November | 66% | 1.8 |
| December | 59% | 1.3 |
Source: NASA POWER solar climatology, 2001-2020 (CERES SYN1deg). Satellite-based, for the 1-degree cell (about 100 km across) around the station, so it describes the area rather than the airport.
How much heating and cooling does Oconomowoc need?
A normal year in Oconomowoc brings 7,089 heating degree days, 32% more than the median U.S. place (5,373), and 643 cooling degree days, 29% fewer than the median (908). Seven months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 2,708 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,407 | 0 |
| February | 1,176 | 0 |
| March | 957 | 1 |
| April | 570 | 3 |
| May | 257 | 37 |
| June | 52 | 133 |
| July | 9 | 218 |
| August | 17 | 177 |
| September | 136 | 67 |
| October | 463 | 7 |
| November | 831 | 0 |
| December | 1,214 | 0 |
| Year (annual) | 7,089 | 643 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00476200. A degree day is one degree of a day's mean temperature below 65°F (heating) or above it (cooling); utilities use them to estimate energy use.
Has Oconomowoc been warmer than normal lately?
2025 averaged 48.3°F, 1.0°F above the 1991-2020 normal of 47.2°F. 2 of the 2 complete years since 2024 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2024 | 51.0°F | +3.8°F | 38.63 | 40.3 |
| 2025 | 48.3°F | +1.0°F | 36.04 | 29.9 |
Over 69 complete years from 1894 to 2025, the station's annual mean temperature rose at a fitted 2.4°F per century (+0.13°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00476200; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Oconomowoc's climate compare?
Oconomowoc is warmer than 142 of the other 164 places with their own NOAA record in Wisconsin, and wetter than 123. Across the 7,247 U.S. stations with normals, its annual mean of 47.2°F is warmer than 29%.
In the Köppen classification computed from these normals, Oconomowoc is Dfa: continental, no dry season, hot summer. What the classes mean.
Places with the most similar year elsewhere
Measured month by month on the normal high, low and precipitation, among places of 20,000 or more people in other states:
Source: NOAA NCEI 1991-2020 normals for every station PlainClimate covers. Similarity: the root-mean-square difference of the 36 monthly figures, precipitation weighted so an inch counts like 6°F.
Which places near Oconomowoc share this climate record?
10 places have no NOAA station with 1991-2020 normals of their own, and this station is the nearest full record. A place's own climate can differ from these figures, by several degrees where it sits much higher or lower than the station, nearer the coast, or inside a large city's heat; for the larger places the next nearest records are named with their yearly mean, so the spread around them is visible, and places of 50,000 or more have their own page with NOAA's gridded normals.
- Delafield, WI7,275 people · 6 mi E
- Summit, WI5,346 people · 4 mi S
- Okauchee Lake, WI4,827 people · 4 mi NE
- Ixonia, WI2,470 people · 5 mi NW
- Nashotah, WI1,313 people · 5 mi E
- Ashippun, WI972 people · 8 mi N
- Oconomowoc Lake, WI569 people · 3 mi E
- Chenequa, WI534 people · 6 mi E
- Lac La Belle, WI281 people · 3 mi N
- North Lake, WI222 people · 8 mi NE
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
Questions about Oconomowoc's climate
What is the coldest month in Oconomowoc?
January, with a normal high of 28°F and a normal low of 11°F. The warmest is July (82°F by day, 61°F at night).
Does it snow in Oconomowoc?
Yes: 40 inches in a normal year, falling on 31 days with 0.1 inch or more, the most in January (11.1 inches).
What is the rainiest month in Oconomowoc?
June, with 4.86 in of precipitation in a normal year; the driest is February with 1.61 in.
What plant hardiness zone is Oconomowoc in?
The USDA's 2023 map puts Oconomowoc in zone 5b in ZIP code 53066. By the same method at Oconomowoc's NOAA station, the coldest night of a typical year reaches −15°F (26 years, 1991-2020): zone 5b.
How late can frost come in Oconomowoc?
In half of years the last 32°F night comes after April 30; in one year in ten it comes after May 17. Waiting until May 17 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Wisconsin climateThe statewide normals and every place in the state
- Sullivan, WI9 miles from this station, 46.6°F a year
- Watertown, WI13 miles from this station, 46.4°F a year
- Waukesha, WI14 miles from this station, 46.5°F a year
- Hartford, WI17 miles from this station, 44.7°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made