USDA Hardiness Zone 5a
Frost Dates for 50025 — Audubon, Iowa
NOAA 1991–2020 normals from Audubon, IA (1,280 ft), 2 miles south.
Updated
In Audubon, the last spring frost (32°F) is around May 2 in half of years and has passed by May 15 in nine years out of ten. The first fall frost comes around October 3, as early as September 19 one year in ten, leaving a typical freeze-free season of 154 days (NOAA, Audubon, IA).
- Last spring frost
- May 2
- First fall frost
- October 3
- Growing season
- 154 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 18
- Last snow
- March 24
- Winters with snow
- 93%
- Snow per year
- —
median, 1991–2020
median, 1991–2020
26 of 28 observed
NOAA normal
Frost risk by date in Audubon
Half of springs at Audubon, IA see their last 32°F night by May 2; only one in ten is past it by April 19, and one in ten still has one after May 15. Planting tender crops after May 6 leaves a 30% risk of a frost on them, after May 9 20%, and after May 15 10%. The 13 days between the even-odds date and the one-in-ten date is narrower than at 42% of the 132 Iowa stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 3 in half of years, as early as September 19 one year in ten, and holds off past October 17 one year in ten. A hard freeze of 28°F follows 11 days later, around October 14; in spring the one-in-ten date for 28°F is May 5, 10 days before the 32°F one. The freeze-free season lasts 154 days in a typical year, shorter than at 84% of the 132 Iowa stations; it reaches 173 days one year in ten and falls short of 135 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 10, and return around September 25. Severe cold of 16°F or below comes every winter, usually between November 10 and March 24.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 28 | May 2 | May 5 | May 7 | May 10 | May 12 | May 15 | May 19 | May 23 |
| 32°F | Apr 19 | Apr 23 | Apr 27 | Apr 30 | May 2 | May 4 | May 6 | May 9 | May 15 |
| 28°F | Apr 8 | Apr 13 | Apr 16 | Apr 19 | Apr 22 | Apr 25 | Apr 28 | May 1 | May 5 |
| 24°F | Mar 30 | Apr 3 | Apr 6 | Apr 8 | Apr 11 | Apr 14 | Apr 17 | Apr 21 | Apr 26 |
| 20°F | Mar 17 | Mar 23 | Mar 28 | Mar 31 | Apr 2 | Apr 5 | Apr 8 | Apr 12 | Apr 17 |
| 16°F | Mar 7 | Mar 12 | Mar 16 | Mar 20 | Mar 24 | Mar 27 | Mar 31 | Apr 2 | Apr 7 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 12 | Sep 16 | Sep 19 | Sep 22 | Sep 25 | Sep 28 | Oct 1 | Oct 4 | Oct 8 |
| 32°F | Sep 19 | Sep 24 | Sep 28 | Oct 1 | Oct 3 | Oct 5 | Oct 9 | Oct 13 | Oct 17 |
| 28°F | Sep 28 | Oct 2 | Oct 6 | Oct 11 | Oct 14 | Oct 16 | Oct 19 | Oct 22 | Oct 26 |
| 24°F | Oct 8 | Oct 15 | Oct 18 | Oct 21 | Oct 23 | Oct 26 | Oct 29 | Nov 1 | Nov 5 |
| 20°F | Oct 18 | Oct 24 | Oct 27 | Oct 30 | Nov 1 | Nov 3 | Nov 6 | Nov 10 | Nov 15 |
| 16°F | Oct 28 | Nov 1 | Nov 4 | Nov 7 | Nov 10 | Nov 13 | Nov 17 | Nov 21 | Nov 27 |
Freeze probabilities 1991–2020 at Audubon, 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 50025 →Compare Audubon with another place →
Weather by month in Audubon
July is the warmest month at Audubon, IA, averaging 83°F by day and 62°F at night; January is the coldest at 28°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 55% of years.
Warmth for growing adds up to 2,779 growing degree days a year (base 50°F), fewer than at 76% of the 132 Iowa stations. 35% of them (969) have built up by the end of June, and July adds the most, 685. Precipitation totals 35.0 inches a year, most in May (5.2") and least in January (0.9"); May to September bring 63% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 28 | 9 | 0.9 | 100% | 31 | 0 |
| Feb | 33 | 13 | 1.1 | 100% | 27 | 1 |
| Mar | 46 | 24 | 1.7 | 100% | 24 | 19 |
| Apr | 60 | 35 | 3.7 | 100% | 12 | 85 |
| May | 70 | 48 | 5.2 | 55% | 1 | 298 |
| Jun | 80 | 58 | 5.1 | 0% | 0 | 566 |
| Jul | 83 | 62 | 3.8 | 0% | 0 | 685 |
| Aug | 81 | 59 | 4.5 | 0% | 0 | 615 |
| Sep | 75 | 50 | 3.5 | 40% | 1 | 377 |
| Oct | 62 | 37 | 2.8 | 100% | 11 | 120 |
| Nov | 46 | 25 | 1.5 | 100% | 23 | 13 |
| Dec | 33 | 14 | 1.2 | 100% | 30 | 0 |
Monthly normals 1991–2020 at Audubon, IA (1,280 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, Harlan, IA, 22 miles west of Audubon, has a last frost 5 days earlier (April 27), a first frost 6 days later (October 9), a season 11 days longer.
When it snows in Audubon, Iowa
The first measurable snow (0.1 inch or more) in Audubon usually arrives around November 18, and the last of the season around March 24. Those are the middle dates across the winters of 1991–2020 at Audubon, IA, 2.4 miles away: half of years saw snow earlier, half later. Snow fell in 93% of those winters. The last 32°F night of spring typically comes 39 days after the last snow.
Planting calendar for 50025
| When | What to do |
|---|---|
| February 21 – March 7 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 7 – March 21 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 4 – April 18 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 2 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 11 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 19 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 3 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 50025 is 2 miles from Audubon, IA, which stands at 1,280 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 50025 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.