USDA Hardiness Zone 7a
Frost Dates for 99357 — Royal City, Washington
NOAA 1991–2020 normals from Smyrna, WA (560 ft), 6 miles south.
Updated
In Royal City, the last spring frost (32°F) is around April 23 in half of years and has passed by May 7 in nine years out of ten. The first fall frost comes around October 12, as early as October 1 one year in ten, leaving a typical freeze-free season of 172 days (NOAA, Smyrna, WA).
- Last spring frost
- April 23
- First fall frost
- October 12
- Growing season
- 172 days
- Hardiness zone
- 7a
50% probability
50% probability
freeze-free, 50%
0 to 5°F (-17.8 to -15.0°C) coldest night
- First snow
- December 27
- Last snow
- January 25
- Winters with snow
- 82%
- Snow per year
- —
median, 1991–2020
median, 1991–2020
14 of 17 observed
NOAA normal
Frost risk by date in Royal City
Half of springs at Smyrna, WA see their last 32°F night by April 23; only one in ten is past it by April 3, and one in ten still has one after May 7. Planting tender crops after April 29 leaves a 30% risk of a frost on them, after May 2 20%, and after May 7 10%. The 14 days between the even-odds date and the one-in-ten date is narrower than at 88% of the 113 Washington stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 12 in half of years, as early as October 1 one year in ten, and holds off past October 25 one year in ten. A hard freeze of 28°F follows 12 days later, around October 24; in spring the one-in-ten date for 28°F is April 24, 13 days before the 32°F one. The freeze-free season lasts 172 days in a typical year, shorter than at 67% of the 113 Washington stations; it reaches 192 days one year in ten and falls short of 152 one year in ten. On average 122 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 13 days longer, to about May 6, and return around October 2. Severe cold of 16°F or below comes in 98% of winters, usually between November 29 and February 8.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 23 | Apr 28 | Apr 30 | May 3 | May 6 | May 8 | May 11 | May 14 | May 18 |
| 32°F | Apr 3 | Apr 11 | Apr 16 | Apr 20 | Apr 23 | Apr 26 | Apr 29 | May 2 | May 7 |
| 28°F | Mar 13 | Mar 21 | Mar 27 | Mar 31 | Apr 3 | Apr 7 | Apr 11 | Apr 17 | Apr 24 |
| 24°F | Feb 24 | Mar 3 | Mar 7 | Mar 11 | Mar 15 | Mar 20 | Mar 26 | Mar 31 | Apr 5 |
| 20°F | Jan 31 | Feb 11 | Feb 18 | Feb 23 | Feb 27 | Mar 1 | Mar 5 | Mar 10 | Mar 18 |
| 16°F98% of yrs | Dec 31 | Jan 16 | Jan 26 | Feb 2 | Feb 8 | Feb 16 | Feb 22 | Feb 28 | Mar 5 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 21 | Sep 25 | Sep 28 | Oct 1 | Oct 2 | Oct 4 | Oct 6 | Oct 10 | Oct 14 |
| 32°F | Oct 1 | Oct 3 | Oct 5 | Oct 8 | Oct 12 | Oct 15 | Oct 18 | Oct 21 | Oct 25 |
| 28°F | Oct 6 | Oct 14 | Oct 17 | Oct 20 | Oct 24 | Oct 26 | Oct 29 | Nov 1 | Nov 6 |
| 24°F | Oct 20 | Oct 25 | Oct 28 | Oct 31 | Nov 2 | Nov 5 | Nov 11 | Nov 17 | Nov 25 |
| 20°F | Oct 29 | Nov 3 | Nov 7 | Nov 12 | Nov 17 | Nov 22 | Nov 27 | Dec 3 | Dec 11 |
| 16°F98% of yrs | Nov 4 | Nov 12 | Nov 18 | Nov 25 | Nov 29 | Dec 4 | Dec 9 | Dec 18 | Dec 30 |
Freeze probabilities 1991–2020 at Smyrna, WA, 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 99357 →Compare Royal City with another place →
Weather by month in Royal City
July is the warmest month at Smyrna, WA, averaging 93°F by day and 59°F at night; December is the coldest at 40°F and 26°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to September the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 25% of years.
Warmth for growing adds up to 3,262 growing degree days a year (base 50°F), more than at 97% of the 113 Washington stations. 33% of them (1,084) have built up by the end of June, and July adds the most, 807.
| Month | High °F | Low °F | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|
| Jan | 40 | 26 | 100% | 26 | 1 |
| Feb | 48 | 28 | 100% | 20 | 2 |
| Mar | 58 | 33 | 100% | 17 | 27 |
| Apr | 67 | 39 | 91% | 6 | 116 |
| May | 77 | 46 | 25% | 1 | 363 |
| Jun | 84 | 55 | 0% | 0 | 575 |
| Jul | 93 | 59 | 0% | 0 | 807 |
| Aug | 92 | 58 | 0% | 0 | 763 |
| Sep | 82 | 49 | 9% | 1 | 459 |
| Oct | 67 | 39 | 95% | 9 | 136 |
| Nov | 50 | 31 | 100% | 18 | 10 |
| Dec | 40 | 26 | 100% | 26 | 2 |
Monthly normals 1991–2020 at Smyrna, WA (560 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, Priest Rapids Dam, WA, 22 miles southwest of Royal City, has a last frost 30 days earlier (March 24), a first frost 23 days later (November 4), a season 50 days longer.
When it snows in Royal City, Washington
The first measurable snow (0.1 inch or more) in Royal City usually arrives around December 27, and the last of the season around January 25. Those are the middle dates across the winters of 1991–2020 at Smyrna, WA, 5.9 miles away: half of years saw snow earlier, half later. Snow fell in 82% of those winters. The last 32°F night of spring typically comes 88 days after the last snow.
Planting calendar for 99357
| When | What to do |
|---|---|
| February 12 – February 26 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| February 26 – March 12 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 26 – April 9 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 23 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 20 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 28 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 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 99357 is 6 miles from Smyrna, WA, which stands at 560 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 99357 in zone 7a, the band where the coldest night of the year averaged 0 to 5°F (-17.8 to -15.0°C) over 1991–2020; a zone describes winter lows, not frost dates.
Frost dates across Washington →
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.