USDA Hardiness Zone 5a
Frost Dates for 52175 — West Union, Iowa
NOAA 1991–2020 normals from Fayette, IA (1,145 ft), 7 miles south.
Updated
In West Union, the last spring frost (32°F) is around May 4 in half of years and has passed by May 17 in nine years out of ten. The first fall frost comes around October 4, as early as September 20 one year in ten, leaving a typical freeze-free season of 151 days (NOAA, Fayette, IA).
- Last spring frost
- May 4
- First fall frost
- October 4
- Growing season
- 151 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 13
- Last snow
- April 2
- Winters with snow
- 100%
- Snow per year
- 41.1"
median, 1991–2020
median, 1991–2020
30 of 30 observed
NOAA normal
Frost risk by date in West Union
Half of springs at Fayette, IA see their last 32°F night by May 4; only one in ten is past it by April 20, and one in ten still has one after May 17. Planting tender crops after May 9 leaves a 30% risk of a frost on them, after May 12 20%, and after May 17 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 4 in half of years, as early as September 20 one year in ten, and holds off past October 18 one year in ten. A hard freeze of 28°F follows 11 days later, around October 15; in spring the one-in-ten date for 28°F is May 8, 9 days before the 32°F one. The freeze-free season lasts 151 days in a typical year, shorter than at 94% of the 132 Iowa stations; it reaches 170 days one year in ten and falls short of 133 one year in ten. On average 164 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 9 days longer, to about May 13, and return around September 25. Severe cold of 16°F or below comes every winter, usually between November 12 and March 25.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 30 | May 5 | May 8 | May 11 | May 13 | May 16 | May 19 | May 23 | May 28 |
| 32°F | Apr 20 | Apr 25 | Apr 29 | May 2 | May 4 | May 7 | May 9 | May 12 | May 17 |
| 28°F | Apr 10 | Apr 15 | Apr 18 | Apr 22 | Apr 25 | Apr 28 | May 1 | May 4 | May 8 |
| 24°F | Mar 30 | Apr 4 | Apr 7 | Apr 10 | Apr 14 | Apr 16 | Apr 21 | Apr 24 | Apr 30 |
| 20°F | Mar 18 | Mar 24 | Mar 30 | Apr 1 | Apr 4 | Apr 6 | Apr 9 | Apr 14 | Apr 20 |
| 16°F | Mar 10 | Mar 15 | Mar 18 | Mar 22 | Mar 25 | Mar 29 | Apr 1 | Apr 4 | Apr 10 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 13 | Sep 17 | Sep 20 | Sep 23 | Sep 25 | Sep 28 | Oct 1 | Oct 3 | Oct 6 |
| 32°F | Sep 20 | Sep 25 | Sep 29 | Oct 1 | Oct 4 | Oct 6 | Oct 9 | Oct 13 | Oct 18 |
| 28°F | Oct 1 | Oct 5 | Oct 9 | Oct 12 | Oct 15 | Oct 18 | Oct 20 | Oct 23 | Oct 27 |
| 24°F | Oct 12 | Oct 18 | Oct 20 | Oct 23 | Oct 25 | Oct 28 | Oct 30 | Nov 1 | Nov 7 |
| 20°F | Oct 22 | Oct 27 | Oct 30 | Nov 1 | Nov 2 | Nov 5 | Nov 8 | Nov 12 | Nov 17 |
| 16°F | Nov 1 | Nov 4 | Nov 7 | Nov 10 | Nov 12 | Nov 15 | Nov 18 | Nov 22 | Nov 27 |
Freeze probabilities 1991–2020 at Fayette, 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 52175 →Compare West Union with another place →
Weather by month in West Union
July is the warmest month at Fayette, IA, averaging 82°F by day and 60°F at night; January is the coldest at 25°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 63% of years.
Warmth for growing adds up to 2,491 growing degree days a year (base 50°F), fewer than at 99% of the 132 Iowa stations. 34% of them (842) have built up by the end of June, and July adds the most, 637. Precipitation totals 39.6 inches a year, most in June (5.9") and least in January (1.2"); May to September bring 61% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 25 | 6 | 1.2 | 100% | 31 | 0 |
| Feb | 29 | 9 | 1.2 | 100% | 27 | 0 |
| Mar | 42 | 22 | 2.1 | 100% | 26 | 11 |
| Apr | 57 | 33 | 4.1 | 100% | 13 | 61 |
| May | 69 | 45 | 5.1 | 63% | 2 | 255 |
| Jun | 79 | 56 | 5.9 | 0% | 0 | 515 |
| Jul | 82 | 60 | 5.3 | 0% | 0 | 637 |
| Aug | 80 | 57 | 4.1 | 0% | 0 | 567 |
| Sep | 74 | 48 | 3.9 | 35% | 1 | 337 |
| Oct | 60 | 36 | 2.9 | 99% | 11 | 98 |
| Nov | 44 | 24 | 2.1 | 100% | 23 | 10 |
| Dec | 31 | 13 | 1.7 | 100% | 30 | 0 |
Monthly normals 1991–2020 at Fayette, IA (1,145 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, Postville, IA, 15 miles northeast of West Union, has a last frost 3 days earlier (May 1), a first frost 1 day earlier (October 3), a season 2 days longer.
When it snows in West Union, Iowa
The first measurable snow (0.1 inch or more) in West Union usually arrives around November 13, and the last of the season around April 2. Those are the middle dates across the winters of 1991–2020 at Fayette, IA, 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 32 days after the last snow.
Planting calendar for 52175
| When | What to do |
|---|---|
| February 23 – March 9 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 9 – March 23 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 6 – April 20 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 4 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 12 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 20 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 4 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 52175 is 7 miles from Fayette, IA, which stands at 1,145 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 52175 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.