USDA Hardiness Zone 5b
Frost Dates for 99664 — Seward, Alaska
NOAA 1991–2020 normals from Seward Airport, AK (22 ft), 2 miles south.
Updated
In Seward, the last spring frost (32°F) is around May 2 in half of years and has passed by May 17 in nine years out of ten. The first fall frost comes around October 7, as early as September 28 one year in ten, leaving a typical freeze-free season of 158 days (NOAA, Seward Airport, AK).
- Last spring frost
- May 2
- First fall frost
- October 7
- Growing season
- 158 days
- Hardiness zone
- 5b
50% probability
50% probability
freeze-free, 50%
-15 to -10°F (-26.1 to -23.3°C) coldest night
- First snow
- November 12
- 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 Seward
Half of springs at Seward Airport, AK see their last 32°F night by May 2; 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 8 leaves a 30% risk of a frost on them, after May 12 20%, and after May 17 10%. The 15 days between the even-odds date and the one-in-ten date is wider than at 70% of the 37 Alaska stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 7 in half of years, as early as September 28 one year in ten, and holds off past October 23 one year in ten. A hard freeze of 28°F follows 14 days later, around October 21; in spring the one-in-ten date for 28°F is April 29, 18 days before the 32°F one. The freeze-free season lasts 158 days in a typical year, longer than at 81% of the 37 Alaska stations; it reaches 175 days one year in ten and falls short of 140 one year in ten. On average 146 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 18 days longer, to about May 20, and return around September 27. Severe cold of 16°F or below comes every winter, usually between November 23 and March 18.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 5 | May 11 | May 15 | May 17 | May 20 | May 23 | May 26 | May 29 | Jun 2 |
| 32°F | Apr 20 | Apr 25 | Apr 28 | Apr 30 | May 2 | May 5 | May 8 | May 12 | May 17 |
| 28°F | Apr 3 | Apr 6 | Apr 9 | Apr 12 | Apr 15 | Apr 17 | Apr 20 | Apr 25 | Apr 29 |
| 24°F | Mar 20 | Mar 27 | Mar 31 | Apr 2 | Apr 4 | Apr 6 | Apr 8 | Apr 13 | Apr 18 |
| 20°F | Mar 8 | Mar 15 | Mar 20 | Mar 24 | Mar 28 | Mar 31 | Apr 2 | Apr 5 | Apr 9 |
| 16°F | Feb 22 | Mar 2 | Mar 9 | Mar 13 | Mar 18 | Mar 22 | Mar 27 | Mar 31 | Apr 3 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 15 | Sep 19 | Sep 22 | Sep 24 | Sep 27 | Sep 29 | Oct 1 | Oct 3 | Oct 8 |
| 32°F | Sep 28 | Oct 1 | Oct 2 | Oct 5 | Oct 7 | Oct 10 | Oct 14 | Oct 17 | Oct 23 |
| 28°F | Oct 5 | Oct 10 | Oct 14 | Oct 18 | Oct 21 | Oct 24 | Oct 27 | Oct 31 | Nov 6 |
| 24°F | Oct 18 | Oct 23 | Oct 27 | Oct 30 | Nov 1 | Nov 5 | Nov 9 | Nov 13 | Nov 19 |
| 20°F | Oct 27 | Nov 1 | Nov 4 | Nov 8 | Nov 12 | Nov 16 | Nov 20 | Nov 23 | Dec 1 |
| 16°F | Nov 6 | Nov 11 | Nov 17 | Nov 20 | Nov 23 | Nov 27 | Dec 1 | Dec 7 | Dec 17 |
Freeze probabilities 1991–2020 at Seward 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 99664 →Compare Seward with another place →
Weather by month in Seward
July is the warmest month at Seward Airport, AK, averaging 62°F by day and 50°F at night; January is the coldest at 31°F and 21°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 56% of years.
Warmth for growing adds up to 539 growing degree days a year (base 50°F), fewer than at 70% of the 37 Alaska stations. 22% of them (118) have built up by the end of June, and July adds the most, 193. Precipitation totals 69.8 inches a year, most in September (9.9") and least in June (2.3"); May to September bring 35% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 31 | 21 | 6.5 | 100% | 25 | 0 |
| Feb | 34 | 24 | 6.4 | 100% | 22 | 0 |
| Mar | 37 | 25 | 3.9 | 100% | 25 | 0 |
| Apr | 45 | 32 | 4.3 | 100% | 13 | 1 |
| May | 53 | 39 | 3.5 | 56% | 2 | 24 |
| Jun | 59 | 46 | 2.3 | 0% | 0 | 93 |
| Jul | 62 | 50 | 3.1 | 0% | 0 | 193 |
| Aug | 62 | 50 | 5.4 | 0% | 0 | 181 |
| Sep | 56 | 43 | 9.9 | 18% | 1 | 45 |
| Oct | 46 | 35 | 8.7 | 98% | 10 | 1 |
| Nov | 36 | 27 | 7.6 | 100% | 22 | 0 |
| Dec | 33 | 23 | 8.2 | 100% | 26 | 0 |
Monthly normals 1991–2020 at Seward Airport, AK (22 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
When it snows in Seward, Alaska
The first measurable snow (0.1 inch or more) in Seward usually arrives around November 12, and the last of the season around April 8. Those are the middle dates across the winters of 1991–2020 at Seward Airport, AK, 1.6 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 24 days after the last snow.
Planting calendar for 99664
| 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 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 99664 is 2 miles from Seward Airport, AK, which stands at 22 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 99664 in zone 5b, the band where the coldest night of the year averaged -15 to -10°F (-26.1 to -23.3°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.