USDA Hardiness Zone 4b
Frost Dates for 57201 — Watertown, South Dakota
NOAA 1991–2020 normals from Watertown Regional Airport, SD (1,748 ft), 2 miles southwest.
Updated
In Watertown, the last spring frost (32°F) is around May 7 in half of years and has passed by May 20 in nine years out of ten. The first fall frost comes around September 30, as early as September 19 one year in ten, leaving a typical freeze-free season of 145 days (NOAA, Watertown Regional Airport, SD).
- Last spring frost
- May 7
- First fall frost
- September 30
- Growing season
- 145 days
- Hardiness zone
- 4b
50% probability
50% probability
freeze-free, 50%
-25 to -20°F (-31.7 to -28.9°C) coldest night
- First snow
- November 3
- Last snow
- April 13
- Winters with snow
- 100%
- Snow per year
- 41.1"
median, 1991–2020
median, 1991–2020
25 of 25 observed
NOAA normal
Frost risk by date in Watertown
Half of springs at Watertown Regional Airport, SD see their last 32°F night by May 7; only one in ten is past it by April 26, and one in ten still has one after May 20. Planting tender crops after May 12 leaves a 30% risk of a frost on them, after May 16 20%, and after May 20 10%. The 13 days between the even-odds date and the one-in-ten date is narrower than at 43% of the 49 South Dakota stations behind this site's ZIP pages.
In fall the first 32°F night comes by September 30 in half of years, as early as September 19 one year in ten, and holds off past October 13 one year in ten. A hard freeze of 28°F follows 9 days later, around October 9; in spring the one-in-ten date for 28°F is May 11, 9 days before the 32°F one. The freeze-free season lasts 145 days in a typical year, shorter than at 67% of the 49 South Dakota stations; it reaches 162 days one year in ten and falls short of 127 one year in ten. On average 174 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 10 days longer, to about May 17, and return around September 23. Severe cold of 16°F or below comes every winter, usually between November 7 and April 3.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 4 | May 8 | May 11 | May 14 | May 17 | May 20 | May 23 | May 26 | May 31 |
| 32°F | Apr 26 | Apr 30 | May 2 | May 4 | May 7 | May 10 | May 12 | May 16 | May 20 |
| 28°F | Apr 14 | Apr 20 | Apr 23 | Apr 27 | Apr 29 | May 1 | May 3 | May 6 | May 11 |
| 24°F | Apr 6 | Apr 10 | Apr 14 | Apr 17 | Apr 20 | Apr 23 | Apr 26 | Apr 29 | May 3 |
| 20°F | Mar 29 | Apr 3 | Apr 5 | Apr 8 | Apr 10 | Apr 13 | Apr 17 | Apr 21 | Apr 26 |
| 16°F | Mar 15 | Mar 23 | Mar 29 | Apr 1 | Apr 3 | Apr 5 | Apr 8 | Apr 11 | Apr 18 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 9 | Sep 14 | Sep 18 | Sep 20 | Sep 23 | Sep 25 | Sep 28 | Sep 30 | Oct 4 |
| 32°F | Sep 19 | Sep 23 | Sep 26 | Sep 28 | Sep 30 | Oct 2 | Oct 5 | Oct 8 | Oct 13 |
| 28°F | Sep 26 | Sep 30 | Oct 3 | Oct 5 | Oct 9 | Oct 11 | Oct 14 | Oct 18 | Oct 22 |
| 24°F | Oct 4 | Oct 9 | Oct 13 | Oct 17 | Oct 20 | Oct 23 | Oct 26 | Oct 29 | Nov 2 |
| 20°F | Oct 15 | Oct 20 | Oct 24 | Oct 27 | Oct 30 | Nov 1 | Nov 4 | Nov 7 | Nov 13 |
| 16°F | Oct 25 | Oct 30 | Nov 1 | Nov 4 | Nov 7 | Nov 10 | Nov 13 | Nov 16 | Nov 22 |
Freeze probabilities 1991–2020 at Watertown Regional Airport, SD, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 57201 →Compare Watertown with another place →
Weather by month in Watertown
July is the warmest month at Watertown Regional Airport, SD, averaging 82°F by day and 60°F at night; January is the coldest at 21°F and 3°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 77% of years.
Warmth for growing adds up to 2,370 growing degree days a year (base 50°F), fewer than at 88% of the 49 South Dakota stations. 32% of them (754) have built up by the end of June, and July adds the most, 651. Precipitation totals 23.1 inches a year, most in June (3.9") and least in January (0.6"); May to September bring 66% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 21 | 3 | 0.6 | 100% | 31 | 0 |
| Feb | 26 | 7 | 0.7 | 100% | 28 | 0 |
| Mar | 39 | 20 | 1.0 | 100% | 27 | 5 |
| Apr | 54 | 32 | 2.1 | 100% | 16 | 42 |
| May | 67 | 45 | 2.9 | 77% | 2 | 223 |
| Jun | 77 | 55 | 3.9 | 1% | 0 | 484 |
| Jul | 82 | 60 | 3.1 | 0% | 0 | 651 |
| Aug | 80 | 58 | 2.9 | 0% | 0 | 574 |
| Sep | 72 | 49 | 2.5 | 51% | 1 | 319 |
| Oct | 56 | 35 | 2.0 | 100% | 12 | 68 |
| Nov | 40 | 21 | 0.7 | 100% | 26 | 4 |
| Dec | 26 | 9 | 0.7 | 100% | 31 | 0 |
Monthly normals 1991–2020 at Watertown Regional Airport, SD (1,748 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
Compared with the next station
The nearest other station, Milbank, SD, 32 miles northeast of Watertown and 606 feet lower, has a last frost 2 days earlier (May 5), a first frost 2 days later (October 2), a season 5 days longer.
When it snows in Watertown, South Dakota
The first measurable snow (0.1 inch or more) in Watertown usually arrives around November 3, and the last of the season around April 13. Those are the middle dates across the winters of 1991–2020 at Watertown Regional Airport, SD, 1.9 miles away: half of years saw snow earlier, half later. Every one of those winters saw snow. The last 32°F night of spring typically comes 24 days after the last snow.
Planting calendar for 57201
| When | What to do |
|---|---|
| February 26 – March 12 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 12 – March 26 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 9 – April 23 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 7 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 8 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 16 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 30 onward | Plant garlic, mulch beds, lift tender bulbsGarlic wants a cold spell; bare soil loses structure over winter. |
The weeks before and after the 50% dates are general rules of thumb, not NOAA figures; a seed packet gives the timing for each variety.
Where these figures come from
ZIP 57201 is 2 miles from Watertown Regional Airport, SD, which stands at 1,748 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 57201 in zone 4b, the band where the coldest night of the year averaged -25 to -20°F (-31.7 to -28.9°C) over 1991–2020; a zone describes winter lows, not frost dates.
Frost dates across South Dakota →
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.