USDA Hardiness Zone 8b
Frost Dates for 97133 — North Plains, Oregon
NOAA 1991–2020 normals from Portland-Hillsboro Airport, OR (204 ft), 9 miles southeast.
Updated
In North Plains, the last spring frost (32°F) is around April 16 in half of years and has passed by May 3 in nine years out of ten. The first fall frost comes around October 23, as early as October 3 one year in ten, leaving a typical freeze-free season of 191 days (NOAA, Portland-Hillsboro Airport, OR).
- Last spring frost
- April 16
- First fall frost
- October 23
- Growing season
- 191 days
- Hardiness zone
- 8b
50% probability
50% probability
freeze-free, 50%
15 to 20°F (-9.4 to -6.7°C) coldest night
- First snow
- Rare
- Last snow
- Rare
- Winters with snow
- 34%
- Snow per year
- 2.7"
median, 1991–2020
median, 1991–2020
10 of 29 observed
NOAA normal
Frost risk by date in North Plains
Half of springs at Portland-Hillsboro Airport, OR see their last 32°F night by April 16; only one in ten is past it by March 25, and one in ten still has one after May 3. Planting tender crops after April 25 leaves a 30% risk of a frost on them, after April 29 20%, and after May 3 10%. The 17 days between the even-odds date and the one-in-ten date is narrower than at 83% of the 103 Oregon stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 23 in half of years, as early as October 3 one year in ten, and holds off past November 18 one year in ten. A hard freeze of 28°F follows 20 days later, around November 12; in spring the one-in-ten date for 28°F is April 9, 24 days before the 32°F one. The freeze-free season lasts 191 days in a typical year, shorter than at 56% of the 103 Oregon stations; it reaches 223 days one year in ten and falls short of 161 one year in ten. On average 64 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 19 days longer, to about May 5, and return around October 6. Nights of 24°F, cold enough to damage hardier plants, come in 98% of winters and 16°F in 29%.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 21 | Apr 26 | Apr 30 | May 2 | May 5 | May 9 | May 14 | May 20 | May 27 |
| 32°F | Mar 25 | Mar 31 | Apr 5 | Apr 11 | Apr 16 | Apr 20 | Apr 25 | Apr 29 | May 3 |
| 28°F | Feb 15 | Feb 25 | Mar 1 | Mar 7 | Mar 13 | Mar 18 | Mar 24 | Mar 31 | Apr 9 |
| 24°F98% of yrs | Dec 31 | Jan 16 | Jan 28 | Feb 6 | Feb 14 | Feb 19 | Feb 23 | Feb 27 | Mar 5 |
| 20°F68% of yrs | Dec 1 | Dec 11 | Dec 22 | Dec 31 | Jan 9 | Jan 24 | Feb 1 | Feb 12 | Feb 20 |
| 16°F29% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 20 | Sep 27 | Oct 1 | Oct 3 | Oct 6 | Oct 9 | Oct 14 | Oct 20 | Oct 31 |
| 32°F | Oct 3 | Oct 9 | Oct 14 | Oct 18 | Oct 23 | Oct 28 | Nov 2 | Nov 8 | Nov 18 |
| 28°F | Oct 20 | Oct 27 | Nov 1 | Nov 7 | Nov 12 | Nov 18 | Nov 25 | Dec 1 | Dec 10 |
| 24°F98% of yrs | Nov 4 | Nov 13 | Nov 20 | Nov 27 | Dec 1 | Dec 9 | Dec 18 | Dec 28 | Jan 11 |
| 20°F68% of yrs | Nov 14 | Nov 27 | Dec 1 | Dec 7 | Dec 14 | Dec 25 | Jan 1 | Jan 14 | Feb 9 |
| 16°F29% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Portland-Hillsboro Airport, OR, 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 97133 →Compare North Plains with another place →
Weather by month in North Plains
July is the warmest month at Portland-Hillsboro Airport, OR, averaging 82°F by day and 52°F at night; December is the coldest at 46°F and 33°F. A freezing night is all but certain in every month from November to March (a 90% chance or more). From June to September the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 73% of years and May still brings one in 16% of years.
Warmth for growing adds up to 2,195 growing degree days a year (base 50°F), fewer than at 54% of the 103 Oregon stations. 29% of them (640) have built up by the end of June, and July adds the most, 532. Precipitation totals 36.1 inches a year, most in December (6.1") and least in July (0.4"); May to September bring 16% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 47 | 34 | 5.3 | 100% | 13 | 3 |
| Feb | 51 | 34 | 4.0 | 100% | 13 | 2 |
| Mar | 56 | 37 | 3.7 | 99% | 9 | 20 |
| Apr | 61 | 39 | 2.6 | 73% | 3 | 65 |
| May | 69 | 45 | 2.0 | 16% | 1 | 217 |
| Jun | 74 | 49 | 1.3 | 0% | 0 | 332 |
| Jul | 82 | 52 | 0.4 | 0% | 0 | 532 |
| Aug | 82 | 52 | 0.5 | 0% | 0 | 530 |
| Sep | 76 | 48 | 1.4 | 5% | <1 | 359 |
| Oct | 64 | 41 | 3.4 | 63% | 3 | 113 |
| Nov | 53 | 37 | 5.4 | 95% | 9 | 17 |
| Dec | 46 | 33 | 6.1 | 100% | 14 | 3 |
Monthly normals 1991–2020 at Portland-Hillsboro Airport, OR (204 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, Forest Grove, OR, 10 miles south of North Plains, has the same 50% last-frost date, a first frost 3 days later (October 26), a season 1 day longer.
When it snows in North Plains, Oregon
Measurable snow is rare here: only 10 of 29 winters from 1991 to 2020 recorded 0.1 inch or more at Forest Grove, OR, 9.9 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 97133
| When | What to do |
|---|---|
| February 5 – February 19 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| February 19 – March 5 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 19 – April 2 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 16 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 31 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by October 9 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 23 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 97133 is 9 miles from Portland-Hillsboro Airport, OR, which stands at 204 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station; its figures are presented in full for 97124 (Hillsboro). The 2023 USDA Plant Hardiness Zone Map lists ZIP 97133 in zone 8b, the band where the coldest night of the year averaged 15 to 20°F (-9.4 to -6.7°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.