USDA Hardiness Zone 5a
Frost Dates for 51106 — Sioux City, Iowa
NOAA 1991–2020 normals from Sioux City Ang, IA (1,100 ft), 5 miles south.
Updated
In Sioux City, the last spring frost (32°F) is around April 29 in half of years and has passed by May 11 in nine years out of ten. The first fall frost comes around October 7, as early as September 24 one year in ten, leaving a typical freeze-free season of 161 days (NOAA, Sioux City Ang, IA).
- Last spring frost
- April 29
- First fall frost
- October 7
- Growing season
- 161 days
- Hardiness zone
- 5a
50% probability
50% probability
freeze-free, 50%
-20 to -15°F (-28.9 to -26.1°C) coldest night
- First snow
- November 7
- Last snow
- April 8
- Winters with snow
- 100%
- Snow per year
- 36"
median, 1991–2020
median, 1991–2020
30 of 30 observed
NOAA normal
Frost risk by date in Sioux City
Half of springs at Sioux City Ang, IA see their last 32°F night by April 29; only one in ten is past it by April 15, and one in ten still has one after May 11. Planting tender crops after May 4 leaves a 30% risk of a frost on them, after May 7 20%, and after May 11 10%. The 12 days between the even-odds date and the one-in-ten date is narrower than at 67% of the 132 Iowa stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 7 in half of years, as early as September 24 one year in ten, and holds off past October 21 one year in ten. A hard freeze of 28°F follows 11 days later, around October 18; in spring the one-in-ten date for 28°F is May 2, 9 days before the 32°F one. The freeze-free season lasts 161 days in a typical year, shorter than at 67% of the 132 Iowa stations; it reaches 178 days one year in ten and falls short of 143 one year in ten. On average 160 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 8 days longer, to about May 7, and return around September 29. Severe cold of 16°F or below comes every winter, usually between November 12 and March 21.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 25 | Apr 30 | May 2 | May 5 | May 7 | May 10 | May 13 | May 16 | May 21 |
| 32°F | Apr 15 | Apr 19 | Apr 23 | Apr 26 | Apr 29 | May 1 | May 4 | May 7 | May 11 |
| 28°F | Apr 5 | Apr 10 | Apr 13 | Apr 16 | Apr 19 | Apr 22 | Apr 25 | Apr 29 | May 2 |
| 24°F | Mar 25 | Apr 1 | Apr 3 | Apr 6 | Apr 9 | Apr 12 | Apr 15 | Apr 19 | Apr 23 |
| 20°F | Mar 14 | Mar 20 | Mar 25 | Mar 29 | Mar 31 | Apr 3 | Apr 6 | Apr 11 | Apr 16 |
| 16°F | Mar 6 | Mar 11 | Mar 15 | Mar 18 | Mar 21 | Mar 26 | Mar 30 | Apr 1 | Apr 7 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 18 | Sep 21 | Sep 24 | Sep 26 | Sep 29 | Oct 1 | Oct 4 | Oct 7 | Oct 11 |
| 32°F | Sep 24 | Sep 28 | Oct 1 | Oct 5 | Oct 7 | Oct 10 | Oct 13 | Oct 16 | Oct 21 |
| 28°F | Oct 2 | Oct 8 | Oct 12 | Oct 15 | Oct 18 | Oct 21 | Oct 23 | Oct 26 | Oct 30 |
| 24°F | Oct 14 | Oct 19 | Oct 22 | Oct 25 | Oct 27 | Oct 30 | Nov 1 | Nov 4 | Nov 9 |
| 20°F | Oct 22 | Oct 26 | Oct 30 | Nov 1 | Nov 4 | Nov 6 | Nov 10 | Nov 14 | Nov 19 |
| 16°F | Oct 30 | Nov 3 | Nov 6 | Nov 10 | Nov 12 | Nov 16 | Nov 19 | Nov 24 | Nov 29 |
Freeze probabilities 1991–2020 at Sioux City Ang, IA, 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 51106 →Compare Sioux City with another place →
Weather by month in Sioux City
July is the warmest month at Sioux City Ang, IA, averaging 86°F by day and 63°F at night; January is the coldest at 30°F and 9°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 43% of years.
Warmth for growing adds up to 3,042 growing degree days a year (base 50°F), more than at 52% of the 132 Iowa stations. 34% of them (1,028) have built up by the end of June, and July adds the most, 759.
| Month | High °F | Low °F | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|
| Jan | 30 | 9 | 100% | 31 | 0 |
| Feb | 35 | 13 | 100% | 28 | 1 |
| Mar | 47 | 24 | 100% | 24 | 19 |
| Apr | 61 | 35 | 100% | 12 | 93 |
| May | 72 | 47 | 43% | 1 | 316 |
| Jun | 82 | 58 | 0% | 0 | 600 |
| Jul | 86 | 63 | 0% | 0 | 759 |
| Aug | 83 | 61 | 0% | 0 | 680 |
| Sep | 77 | 51 | 27% | <1 | 428 |
| Oct | 64 | 37 | 100% | 11 | 135 |
| Nov | 47 | 24 | 100% | 24 | 12 |
| Dec | 34 | 14 | 100% | 30 | 0 |
Monthly normals 1991–2020 at Sioux City Ang, IA (1,100 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, Sioux City Gateway Airport, IA, 5 miles south of Sioux City, has the same 50% last-frost date, a first frost 2 days earlier (October 5), a season 2 days shorter.
When it snows in Sioux City, Iowa
The first measurable snow (0.1 inch or more) in Sioux City usually arrives around November 7, and the last of the season around April 8. Those are the middle dates across the winters of 1991–2020 at Sioux City Gateway Airport, IA, 5.3 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 21 days after the last snow.
Planting calendar for 51106
| When | What to do |
|---|---|
| February 18 – March 4 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 4 – March 18 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 1 – April 15 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 29 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 15 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 23 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 7 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 51106 is 5 miles from Sioux City Ang, IA, which stands at 1,100 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 9 other ZIP codes share the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 51106 in zone 5a, the band where the coldest night of the year averaged -20 to -15°F (-28.9 to -26.1°C) over 1991–2020; a zone describes winter lows, not frost dates.
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.