USDA Hardiness Zone 5a
Frost Dates for 50436 — Forest City, Iowa
NOAA 1991–2020 normals from Forest City 2 NNE, IA (1,280 ft), 2 miles northeast.
Updated
In Forest City, the last spring frost (32°F) is around April 30 in half of years and has passed by May 10 in nine years out of ten. The first fall frost comes around October 7, as early as September 22 one year in ten, leaving a typical freeze-free season of 159 days (NOAA, Forest City 2 NNE, IA).
- Last spring frost
- April 30
- First fall frost
- October 7
- Growing season
- 159 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 21
- Last snow
- March 27
- Winters with snow
- 100%
- Snow per year
- —
median, 1991–2020
median, 1991–2020
25 of 25 observed
NOAA normal
Frost risk by date in Forest City
Half of springs at Forest City 2 NNE, 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 10. Planting tender crops after May 4 leaves a 30% risk of a frost on them, after May 7 20%, and after May 10 10%. The 10 days between the even-odds date and the one-in-ten date is the narrowest of the 132 Iowa stations behind this site's ZIP pages, so the end of frost is fairly predictable.
In fall the first 32°F night comes by October 7 in half of years, as early as September 22 one year in ten, and holds off past October 20 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 1, 9 days before the 32°F one. The freeze-free season lasts 159 days in a typical year, shorter than at 73% of the 132 Iowa stations; it reaches 178 days one year in ten and falls short of 141 one year in ten. On average 159 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 28. Severe cold of 16°F or below comes every winter, usually between November 12 and March 23.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 27 | May 1 | May 4 | May 6 | May 8 | May 11 | May 13 | May 16 | May 20 |
| 32°F | Apr 14 | Apr 19 | Apr 23 | Apr 27 | Apr 30 | May 1 | May 4 | May 7 | May 10 |
| 28°F | Apr 5 | Apr 9 | Apr 13 | Apr 16 | Apr 18 | Apr 21 | Apr 24 | Apr 27 | May 1 |
| 24°F | Mar 27 | Apr 1 | Apr 4 | Apr 6 | Apr 9 | Apr 11 | Apr 15 | Apr 18 | Apr 23 |
| 20°F | Mar 15 | Mar 21 | Mar 26 | Mar 31 | Apr 2 | Apr 5 | Apr 7 | Apr 10 | Apr 16 |
| 16°F | Mar 7 | Mar 13 | Mar 16 | Mar 20 | Mar 23 | Mar 28 | Apr 1 | Apr 4 | Apr 8 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 15 | Sep 20 | Sep 23 | Sep 26 | Sep 28 | Oct 1 | Oct 3 | Oct 5 | Oct 10 |
| 32°F | Sep 22 | Sep 28 | Oct 1 | Oct 4 | Oct 7 | Oct 9 | Oct 12 | Oct 15 | Oct 20 |
| 28°F | Oct 3 | Oct 8 | Oct 12 | Oct 16 | Oct 18 | Oct 21 | Oct 23 | Oct 26 | Oct 30 |
| 24°F | Oct 15 | Oct 19 | Oct 23 | Oct 25 | Oct 28 | Oct 30 | Nov 1 | Nov 5 | Nov 10 |
| 20°F | Oct 23 | Oct 29 | Nov 1 | Nov 2 | Nov 5 | Nov 7 | Nov 10 | Nov 13 | Nov 19 |
| 16°F | Nov 1 | Nov 4 | Nov 6 | Nov 9 | Nov 12 | Nov 15 | Nov 19 | Nov 23 | Nov 28 |
Freeze probabilities 1991–2020 at Forest City 2 NNE, 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 50436 →Compare Forest City with another place →
Weather by month in Forest City
July is the warmest month at Forest City 2 NNE, 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 2,601 growing degree days a year (base 50°F), fewer than at 92% of the 132 Iowa stations. 34% of them (886) have built up by the end of June, and July adds the most, 663.
| Month | High °F | Low °F | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|
| Jan | 23 | 6 | 100% | 31 | 0 |
| Feb | 27 | 10 | 100% | 27 | 0 |
| Mar | 40 | 23 | 100% | 25 | 10 |
| Apr | 56 | 34 | 100% | 11 | 63 |
| May | 69 | 47 | 46% | 1 | 271 |
| Jun | 78 | 58 | 0% | 0 | 541 |
| Jul | 81 | 62 | 0% | 0 | 663 |
| Aug | 79 | 59 | 0% | 0 | 584 |
| Sep | 73 | 50 | 28% | <1 | 356 |
| Oct | 60 | 37 | 99% | 10 | 102 |
| Nov | 43 | 24 | 100% | 23 | 9 |
| Dec | 29 | 13 | 100% | 30 | 0 |
Monthly normals 1991–2020 at Forest City 2 NNE, 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, Britt 3E, IA, 12 miles southwest of Forest City, has a last frost 1 day earlier (April 29), the same first-frost date, a season 2 days longer.
When it snows in Forest City, Iowa
The first measurable snow (0.1 inch or more) in Forest City usually arrives around November 21, and the last of the season around March 27. Those are the middle dates across the winters of 1991–2020 at Forest City 2 NNE, IA, 2.2 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 34 days after the last snow.
Planting calendar for 50436
| 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 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 50436 is 2 miles from Forest City 2 NNE, IA, which stands at 1,280 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 50436 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.