Will Pipes Freeze in Sully County, SD? 99 nights a Year
Freeze nights in Sully County
In a normal year Sully County, SD gets 99 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 91% of US counties.
Risk level: Severe. The risk season runs October to April, worst in January.
It depends where the pipe is
| Pipe | Freezes near | Nights a year |
|---|---|---|
| Outdoor spigot, open crawlspace | 32°F | 172 nights |
| Bare pipe in garage, attic or outside wall | 20°F | 99 nights |
| Insulated pipe in unheated space | 10°F | 54 nights |
| Inside the heated house | 0°F | 28 nights |
Foam-sleeving a bare pipe in unheated space takes it from 99 nights of risk to 54 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 10/02, last around 05/08. For 20°F: 10/31 to 04/07.
How cold Sully County nights get
Average winter (Dec-Feb) low: 10°F; the coldest month, January, averages 7°F overnight. 9 months normally bring at least one night below 32°F (Jan, Feb, Mar, Apr, May, Sep, Oct, Nov, Dec). Nights below 10°F, cold enough to freeze insulated pipe in an unheated space, come in January, February, March, April, November, December: 54 nights a year, and 28 nights below zero.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 7°F | 11°F | 22°F | 33°F | 45°F | 56°F | 61°F | 59°F | 49°F | 36°F | 23°F | 12°F |
Sully County next to its neighbours
Potter County, SD, 39 km north, gets 105 nights below 20°F to Sully County's 99 nights. Hyde County, SD, 56 km east, gets 97 nights.
| County | Distance | Below 32°F | Below 20°F | Jan low |
|---|---|---|---|---|
| Sully County, SD | - | 172 nights | 99 nights | 7°F |
| Potter County, SD | 39 km north | 176 nights | 105 nights | 5°F |
| Hughes County, SD | 40 km south | 180 nights | 106 nights | 5°F |
| Hyde County, SD | 56 km east | 170 nights | 97 nights | 7°F |
| Stanley County, SD | 60 km southwest | 167 nights | 94 nights | 8°F |
| Dewey County, SD | 73 km northwest | 170 nights | 94 nights | 8°F |
| Walworth County, SD | 79 km north | 178 nights | 105 nights | 4°F |
Sully County within SD
Sully County ranks 25 of 66 SD counties for nights below 20°F. The most is Codington County, SD at 113 nights, with a 6°F average winter low. The fewest is Tripp County, SD: 75 nights, winter lows near 15°F. At 1,865 ft, Sully County sits 80 ft above the state's median county elevation of 1,785 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 Onida (4 mi NW), SD, 2 km away (close match). A normal year, not tonight's forecast: check the forecast low for the night itself. Why elevation is part of the blend: how county numbers are made.