Will Pipes Freeze in Rock County, WI? 71 nights a Year
Freeze nights in Rock County
In a normal year Rock County, WI gets 71 nights at or below 20°F, the point where bare pipes in a garage, attic or outside wall start to freeze. That is more than 77% of US counties.
Risk level: Severe. The risk season runs November to April, worst in January.
It depends where the pipe is
| Pipe | Freezes near | Nights a year |
|---|---|---|
| Outdoor spigot, open crawlspace | 32°F | 147 nights |
| Bare pipe in garage, attic or outside wall | 20°F | 71 nights |
| Insulated pipe in unheated space | 10°F | 36 nights |
| Inside the heated house | 0°F | 16 nights |
Foam-sleeving a bare pipe in unheated space takes it from 71 nights of risk to 36 nights. A 12 ft heat-tape kit runs $17 to $37; an average burst-pipe repair is about $500.
Month by month
Nights at or below 20°F in a normal year.
First 32°F night is usually around 10/15, last around 04/26. For 20°F: 11/15 to 03/24.
How cold Rock County nights get
Average winter (Dec-Feb) low: 15°F; the coldest month, January, averages 11°F overnight. 8 months normally bring at least one night below 32°F (Jan, Feb, Mar, Apr, May, Oct, Nov, Dec). Nights below 10°F, cold enough to freeze insulated pipe in an unheated space, come in January, February, March, November, December: 36 nights a year, and 16 nights below zero.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 11°F | 15°F | 25°F | 36°F | 48°F | 58°F | 62°F | 59°F | 51°F | 39°F | 28°F | 18°F |
Rock County next to its neighbours
Green County, WI, 43 km west, gets 74 nights below 20°F to Rock County's 71 nights. Winnebago County, IL, 38 km south, gets 65 nights.
| County | Distance | Below 32°F | Below 20°F | Jan low |
|---|---|---|---|---|
| Rock County, WI | - | 147 nights | 71 nights | 11°F |
| Winnebago County, IL | 38 km south | 140 nights | 65 nights | 13°F |
| Green County, WI | 43 km west | 150 nights | 74 nights | 11°F |
| Walworth County, WI | 44 km east | 141 nights | 61 nights | 14°F |
| Boone County, IL | 44 km southeast | 146 nights | 70 nights | 12°F |
| Jefferson County, WI | 45 km northeast | 144 nights | 73 nights | 11°F |
| Dane County, WI | 52 km northwest | 155 nights | 79 nights | 11°F |
Rock County within WI
Rock County ranks 66 of 72 WI counties for nights below 20°F. The most is Vilas County, WI at 116 nights, with a 4°F average winter low. The fewest is Racine County, WI: 55 nights, winter lows near 19°F. At 871 ft, Rock County sits 124 ft below the state's median county elevation of 995 ft.
What to do here
- Treat it as a building fix, not a night-of routine: insulate, heat tape, seal crawlspace vents.
- An automatic leak shutoff pays for itself if one burst is avoided.
- Know where the main shutoff is before the first hard freeze.
At this many nights, foam alone is not the answer: insulate or heat tape?.
Where this comes from
NOAA 1991-2020 climate normals, blended from 3 nearby stations and adjusted for elevation; closest is Afton - Janesville Wastewater Plant, WI, 4 km away (close match). A normal year, not tonight's forecast: check the forecast low for the night itself. How a county figure is built from stations: how the numbers are made.