USDA Hardiness Zone 5a
Frost Dates for 99611 — Kenai, Alaska
NOAA 1991–2020 normals from Kenai Municipal Airport, AK (91 ft), under a mile south.
Updated
In Kenai, the last spring frost (32°F) is around May 24 in half of years and has passed by June 4 in nine years out of ten. The first fall frost comes around September 12, as early as August 29 one year in ten, leaving a typical freeze-free season of 110 days (NOAA, Kenai Municipal Airport, AK).
- Last spring frost
- May 24
- First fall frost
- September 12
- Growing season
- 110 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
- October 22
- Last snow
- April 8
- Winters with snow
- 100%
- Snow per year
- —
median, 1991–2020
median, 1991–2020
15 of 15 observed
NOAA normal
Frost risk by date in Kenai
Half of springs at Kenai Municipal Airport, AK see their last 32°F night by May 24; only one in ten is past it by May 8, and one in ten still has one after June 4. Planting tender crops after May 29 leaves a 30% risk of a frost on them, after May 31 20%, and after June 4 10%. The 11 days between the even-odds date and the one-in-ten date is narrower than at 84% of the 37 Alaska stations behind this site's ZIP pages.
In fall the first 32°F night comes by September 12 in half of years, as early as August 29 one year in ten, and holds off past September 27 one year in ten. A hard freeze of 28°F follows 13 days later, around September 25; in spring the one-in-ten date for 28°F is May 18, 17 days before the 32°F one. The freeze-free season lasts 110 days in a typical year, shorter than at 81% of the 37 Alaska stations; it reaches 131 days one year in ten and falls short of 89 one year in ten. On average 197 nights a year drop to 32°F or below. Severe cold of 16°F or below comes every winter, usually between October 26 and April 4.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | too rare for a date | ||||||||
| 32°F | May 8 | May 13 | May 17 | May 21 | May 24 | May 26 | May 29 | May 31 | Jun 4 |
| 28°F | Apr 22 | Apr 27 | Apr 30 | May 2 | May 5 | May 8 | May 11 | May 14 | May 18 |
| 24°F | Apr 8 | Apr 13 | Apr 15 | Apr 18 | Apr 21 | Apr 24 | Apr 28 | Apr 30 | May 3 |
| 20°F | Apr 1 | Apr 3 | Apr 6 | Apr 8 | Apr 10 | Apr 13 | Apr 16 | Apr 20 | Apr 26 |
| 16°F | Mar 23 | Mar 29 | Apr 1 | Apr 3 | Apr 4 | Apr 6 | Apr 9 | Apr 13 | Apr 19 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | too rare for a date | ||||||||
| 32°F | Aug 29 | Sep 1 | Sep 4 | Sep 7 | Sep 12 | Sep 15 | Sep 19 | Sep 23 | Sep 27 |
| 28°F | Sep 7 | Sep 13 | Sep 18 | Sep 22 | Sep 25 | Sep 28 | Oct 1 | Oct 5 | Oct 10 |
| 24°F | Sep 20 | Sep 26 | Oct 1 | Oct 3 | Oct 6 | Oct 9 | Oct 14 | Oct 17 | Oct 22 |
| 20°F | Oct 1 | Oct 5 | Oct 9 | Oct 13 | Oct 17 | Oct 20 | Oct 23 | Oct 28 | Nov 1 |
| 16°F | Oct 8 | Oct 15 | Oct 19 | Oct 23 | Oct 26 | Oct 29 | Nov 1 | Nov 4 | Nov 10 |
Freeze probabilities 1991–2020 at Kenai Municipal Airport, AK, 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 99611 →Compare Kenai with another place →
Weather by month in Kenai
July is the warmest month at Kenai Municipal Airport, AK, averaging 63°F by day and 49°F at night; January is the coldest at 22°F and 7°F. A freezing night is all but certain in every month from September to May (a 90% chance or more). July is the only month with under a 10% chance of a 32°F night. In spring, June still brings one in 20% of years.
Warmth for growing adds up to 470 growing degree days a year (base 50°F), fewer than at 84% of the 37 Alaska stations. 20% of them (96) have built up by the end of June, and July adds the most, 188. Precipitation totals 18.3 inches a year, most in September (3.6") and least in March (0.6"); May to September bring 56% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 22 | 7 | 0.9 | 100% | 30 | 0 |
| Feb | 28 | 12 | 0.8 | 100% | 27 | 0 |
| Mar | 33 | 14 | 0.6 | 100% | 29 | 0 |
| Apr | 44 | 28 | 0.6 | 100% | 21 | 0 |
| May | 55 | 36 | 0.8 | 96% | 8 | 12 |
| Jun | 60 | 44 | 1.2 | 20% | <1 | 84 |
| Jul | 63 | 49 | 2.0 | 0% | 0 | 188 |
| Aug | 63 | 47 | 2.7 | 14% | <1 | 153 |
| Sep | 56 | 40 | 3.6 | 94% | 6 | 31 |
| Oct | 43 | 29 | 2.6 | 100% | 19 | 2 |
| Nov | 30 | 16 | 1.4 | 100% | 27 | 0 |
| Dec | 25 | 11 | 1.1 | 100% | 30 | 0 |
Monthly normals 1991–2020 at Kenai Municipal Airport, AK (91 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, Soldotna 5SSW, AK, 12 miles south of Kenai, has a last frost 18 days later (June 11), a first frost 11 days earlier (September 1), a season 35 days shorter.
When it snows in Kenai, Alaska
The first measurable snow (0.1 inch or more) in Kenai usually arrives around October 22, and the last of the season around April 8. Those are the middle dates across the winters of 1991–2020 at Kenai 9N, AK, 6.4 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 46 days after the last snow.
Planting calendar for 99611
| When | What to do |
|---|---|
| March 15 – March 29 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 29 – April 12 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 26 – May 10 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 24 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by June 20 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by August 29 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 12 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 99611 is under a mile from Kenai Municipal Airport, AK, which stands at 91 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 99611 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.