USDA Hardiness Zone 5b
Frost Dates for 57706 — Ellsworth Afb, South Dakota
NOAA 1991–2020 normals from Rapid City Regional Airport, SD (3,160 ft), 7 miles south.
Updated
In Ellsworth Afb, the last spring frost (32°F) is around May 12 in half of years and has passed by May 26 in nine years out of ten. The first fall frost comes around October 1, as early as September 16 one year in ten, leaving a typical freeze-free season of 139 days (NOAA, Rapid City Regional Airport, SD).
- Last spring frost
- May 12
- First fall frost
- October 1
- Growing season
- 139 days
- Hardiness zone
- 5b
50% probability
50% probability
freeze-free, 50%
-15 to -10°F (-26.1 to -23.3°C) coldest night
- First snow
- November 2
- Last snow
- April 25
- Winters with snow
- 100%
- Snow per year
- 48.5"
median, 1991–2020
median, 1991–2020
23 of 23 observed
NOAA normal
Frost risk by date in Ellsworth Afb
Half of springs at Rapid City Regional Airport, SD see their last 32°F night by May 12; only one in ten is past it by May 1, and one in ten still has one after May 26. Planting tender crops after May 18 leaves a 30% risk of a frost on them, after May 21 20%, and after May 26 10%. The 14 days between the even-odds date and the one-in-ten date is wider than at 59% of the 49 South Dakota stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 1 in half of years, as early as September 16 one year in ten, and holds off past October 14 one year in ten. A hard freeze of 28°F follows 8 days later, around October 9; in spring the one-in-ten date for 28°F is May 14, 12 days before the 32°F one. The freeze-free season lasts 139 days in a typical year, shorter than at 86% of the 49 South Dakota stations; it reaches 157 days one year in ten and falls short of 120 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 22, and return around September 21. Severe cold of 16°F or below comes every winter, usually between November 3 and March 31.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 10 | May 14 | May 17 | May 20 | May 22 | May 25 | May 28 | Jun 1 | Jun 6 |
| 32°F | May 1 | May 4 | May 7 | May 9 | May 12 | May 14 | May 18 | May 21 | May 26 |
| 28°F | Apr 18 | Apr 24 | Apr 28 | Apr 30 | May 2 | May 4 | May 6 | May 10 | May 14 |
| 24°F | Apr 5 | Apr 10 | Apr 14 | Apr 17 | Apr 20 | Apr 24 | Apr 27 | Apr 30 | May 3 |
| 20°F | Mar 23 | Mar 30 | Apr 3 | Apr 6 | Apr 9 | Apr 13 | Apr 17 | Apr 20 | Apr 25 |
| 16°F | Mar 11 | Mar 17 | Mar 22 | Mar 27 | Mar 31 | Apr 3 | Apr 6 | Apr 9 | Apr 16 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 7 | Sep 13 | Sep 16 | Sep 18 | Sep 21 | Sep 23 | Sep 26 | Sep 30 | Oct 3 |
| 32°F | Sep 16 | Sep 21 | Sep 25 | Sep 28 | Oct 1 | Oct 3 | Oct 5 | Oct 9 | Oct 14 |
| 28°F | Sep 26 | Sep 30 | Oct 3 | Oct 6 | Oct 9 | Oct 13 | Oct 16 | Oct 19 | Oct 23 |
| 24°F | Oct 3 | Oct 9 | Oct 14 | Oct 17 | Oct 19 | Oct 22 | Oct 25 | Oct 28 | Nov 1 |
| 20°F | Oct 12 | Oct 17 | Oct 20 | Oct 24 | Oct 26 | Oct 29 | Nov 1 | Nov 4 | Nov 9 |
| 16°F | Oct 18 | Oct 24 | Oct 28 | Oct 31 | Nov 3 | Nov 6 | Nov 10 | Nov 13 | Nov 18 |
Freeze probabilities 1991–2020 at Rapid City 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 57706 →Compare Ellsworth Afb with another place →
Weather by month in Ellsworth Afb
July is the warmest month at Rapid City Regional Airport, SD, averaging 86°F by day and 59°F at night; January is the coldest at 36°F and 13°F. A freezing night is all but certain in every month from October to May (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month.
Warmth for growing adds up to 2,482 growing degree days a year (base 50°F), fewer than at 73% of the 49 South Dakota stations. 28% of them (686) have built up by the end of June, and July adds the most, 696. Precipitation totals 17.6 inches a year, most in May (3.5") and least in January (0.3"); May to September bring 65% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 36 | 13 | 0.3 | 100% | 30 | 0 |
| Feb | 38 | 14 | 0.5 | 100% | 27 | 2 |
| Mar | 48 | 23 | 0.9 | 100% | 26 | 13 |
| Apr | 57 | 31 | 2.1 | 100% | 16 | 45 |
| May | 67 | 42 | 3.5 | 91% | 4 | 185 |
| Jun | 78 | 52 | 2.9 | 3% | 0 | 441 |
| Jul | 86 | 59 | 2.3 | 0% | 0 | 696 |
| Aug | 85 | 56 | 1.6 | 0% | 0 | 645 |
| Sep | 76 | 46 | 1.2 | 50% | 1 | 355 |
| Oct | 60 | 34 | 1.4 | 100% | 13 | 89 |
| Nov | 47 | 22 | 0.5 | 100% | 26 | 11 |
| Dec | 37 | 14 | 0.4 | 100% | 30 | 0 |
Monthly normals 1991–2020 at Rapid City Regional Airport, SD (3,160 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, Rapid City WFO, SD, 8 miles southwest of Ellsworth Afb and 219 feet higher, has a last frost 9 days earlier (May 3), a first frost 7 days later (October 8), a season 18 days longer.
When it snows in Ellsworth Afb, South Dakota
The first measurable snow (0.1 inch or more) in Ellsworth Afb usually arrives around November 2, and the last of the season around April 25. Those are the middle dates across the winters of 1991–2020 at Rapid City Regional Airport, SD, 7.1 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 17 days after the last snow.
Planting calendar for 57706
| When | What to do |
|---|---|
| March 3 – March 17 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 17 – March 31 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 14 – April 28 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 12 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 9 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 17 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 1 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 57706 is 7 miles from Rapid City Regional Airport, SD, which stands at 3,160 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 3 other ZIP codes share the station; its figures are presented in full for 57703 (Rapid City). The 2023 USDA Plant Hardiness Zone Map lists ZIP 57706 in zone 5b, the band where the coldest night of the year averaged -15 to -10°F (-26.1 to -23.3°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.