USDA Hardiness Zone 5a
Frost Dates for 50472 — Saint Ansgar, Iowa
NOAA 1991–2020 normals from Osage, IA (1,170 ft), 11 miles southeast.
Updated
In Saint Ansgar, the last spring frost (32°F) is around April 30 in half of years and has passed by May 12 in nine years out of ten. The first fall frost comes around October 9, as early as September 25 one year in ten, leaving a typical freeze-free season of 163 days (NOAA, Osage, IA).
- Last spring frost
- April 30
- First fall frost
- October 9
- Growing season
- 163 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 27
- Last snow
- March 26
- Winters with snow
- 100%
- Snow per year
- 39.6"
median, 1991–2020
median, 1991–2020
30 of 30 observed
NOAA normal
Frost risk by date in Saint Ansgar
Half of springs at Osage, IA see their last 32°F night by April 30; only one in ten is past it by April 14, and one in ten still has one after May 12. Planting tender crops after May 4 leaves a 30% risk of a frost on them, after May 7 20%, and after May 12 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 9 in half of years, as early as September 25 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 20; in spring the one-in-ten date for 28°F is April 30, 12 days before the 32°F one. The freeze-free season lasts 163 days in a typical year, shorter than at 58% of the 132 Iowa stations; it reaches 182 days one year in ten and falls short of 144 one year in ten. On average 156 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 8, and return around September 30. Severe cold of 16°F or below comes every winter, usually between November 14 and March 23.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 25 | May 1 | May 3 | May 6 | May 8 | May 10 | May 13 | May 16 | May 21 |
| 32°F | Apr 14 | Apr 19 | Apr 22 | Apr 26 | Apr 30 | May 2 | May 4 | May 7 | May 12 |
| 28°F | Apr 3 | Apr 7 | Apr 10 | Apr 14 | Apr 17 | Apr 20 | Apr 23 | Apr 27 | Apr 30 |
| 24°F | Mar 24 | Mar 31 | Apr 2 | Apr 4 | Apr 7 | Apr 9 | Apr 13 | Apr 17 | Apr 22 |
| 20°F | Mar 14 | Mar 20 | Mar 24 | Mar 28 | Mar 31 | Apr 2 | Apr 5 | Apr 8 | Apr 14 |
| 16°F | Mar 8 | Mar 13 | Mar 16 | Mar 20 | Mar 23 | Mar 27 | Mar 31 | Apr 2 | Apr 7 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 17 | Sep 21 | Sep 25 | Sep 27 | Sep 30 | Oct 2 | Oct 4 | Oct 8 | Oct 12 |
| 32°F | Sep 25 | Sep 29 | Oct 3 | Oct 6 | Oct 9 | Oct 11 | Oct 14 | Oct 17 | Oct 21 |
| 28°F | Oct 5 | Oct 10 | Oct 14 | Oct 17 | Oct 20 | Oct 22 | Oct 24 | Oct 27 | Nov 1 |
| 24°F | Oct 17 | Oct 22 | Oct 24 | Oct 27 | Oct 30 | Nov 1 | Nov 3 | Nov 7 | Nov 12 |
| 20°F | Oct 27 | Oct 31 | Nov 2 | Nov 5 | Nov 7 | Nov 10 | Nov 13 | Nov 16 | Nov 22 |
| 16°F | Nov 2 | Nov 6 | Nov 9 | Nov 11 | Nov 14 | Nov 18 | Nov 21 | Nov 25 | Nov 30 |
Freeze probabilities 1991–2020 at Osage, 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 50472 →Compare Saint Ansgar with another place →
Weather by month in Saint Ansgar
July is the warmest month at Osage, IA, averaging 81°F by day and 62°F at night; January is the coldest at 23°F and 6°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 46% of years.
Warmth for growing adds up to 2,618 growing degree days a year (base 50°F), fewer than at 92% of the 132 Iowa stations. 34% of them (887) have built up by the end of June, and July adds the most, 668. Precipitation totals 37.7 inches a year, most in June (5.6") and least in January (1.2"); May to September bring 62% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 23 | 6 | 1.2 | 100% | 31 | 0 |
| Feb | 28 | 10 | 1.3 | 100% | 27 | 0 |
| Mar | 41 | 23 | 1.9 | 100% | 25 | 11 |
| Apr | 56 | 35 | 4.0 | 99% | 11 | 64 |
| May | 68 | 47 | 5.2 | 46% | 1 | 271 |
| Jun | 78 | 58 | 5.6 | 0% | 0 | 542 |
| Jul | 81 | 62 | 5.0 | 0% | 0 | 668 |
| Aug | 79 | 59 | 4.0 | 0% | 0 | 591 |
| Sep | 73 | 50 | 3.5 | 22% | <1 | 359 |
| Oct | 60 | 38 | 2.7 | 99% | 9 | 104 |
| Nov | 43 | 25 | 1.8 | 100% | 23 | 9 |
| Dec | 29 | 14 | 1.5 | 100% | 30 | 0 |
Monthly normals 1991–2020 at Osage, IA (1,170 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, Northwood, IA, 15 miles west of Saint Ansgar, has a last frost 4 days later (May 4), a first frost 5 days earlier (October 4), a season 11 days shorter.
When it snows in Saint Ansgar, Iowa
The first measurable snow (0.1 inch or more) in Saint Ansgar usually arrives around November 27, and the last of the season around March 26. Those are the middle dates across the winters of 1991–2020 at Osage, IA, 10.7 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 35 days after the last snow.
Planting calendar for 50472
| When | What to do |
|---|---|
| February 19 – March 5 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 5 – March 19 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 2 – April 16 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 30 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 17 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 25 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 9 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 50472 is 11 miles from Osage, IA, which stands at 1,170 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station; its figures are presented in full for 50461 (Osage). The 2023 USDA Plant Hardiness Zone Map lists ZIP 50472 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.