USDA Hardiness Zone 8b
Frost Dates for 97116 — Forest Grove, Oregon
NOAA 1991–2020 normals from Forest Grove, OR (180 ft), 2 miles southeast.
Updated
In Forest Grove, the last spring frost (32°F) is around April 16 in half of years and has passed by May 5 in nine years out of ten. The first fall frost comes around October 26, as early as October 6 one year in ten, leaving a typical freeze-free season of 192 days (NOAA, Forest Grove, OR).
- Last spring frost
- April 16
- First fall frost
- October 26
- Growing season
- 192 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 Forest Grove
Half of springs at Forest Grove, OR see their last 32°F night by April 16; only one in ten is past it by March 26, and one in ten still has one after May 5. Planting tender crops after April 26 leaves a 30% risk of a frost on them, after April 30 20%, and after May 5 10%. The 19 days between the even-odds date and the one-in-ten date is narrower than at 70% of the 103 Oregon stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 26 in half of years, as early as October 6 one year in ten, and holds off past November 14 one year in ten. A hard freeze of 28°F follows 16 days later, around November 11; in spring the one-in-ten date for 28°F is April 12, 23 days before the 32°F one. The freeze-free season lasts 192 days in a typical year, shorter than at 55% of the 103 Oregon stations; it reaches 222 days one year in ten and falls short of 165 one year in ten. On average 61 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 4, and return around October 8. Nights of 24°F, cold enough to damage hardier plants, come in 99% of winters and 16°F in 48%.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 19 | Apr 26 | Apr 29 | May 1 | May 4 | May 7 | May 12 | May 17 | May 25 |
| 32°F | Mar 26 | Apr 1 | Apr 6 | Apr 11 | Apr 16 | Apr 20 | Apr 26 | Apr 30 | May 5 |
| 28°F | Feb 21 | Feb 28 | Mar 6 | Mar 13 | Mar 19 | Mar 24 | Mar 30 | Apr 3 | Apr 12 |
| 24°F99% of yrs | Jan 5 | Jan 21 | Feb 1 | Feb 11 | Feb 17 | Feb 23 | Feb 28 | Mar 3 | Mar 16 |
| 20°F85% of yrs | Dec 8 | Dec 19 | Jan 1 | Jan 7 | Jan 18 | Jan 30 | Feb 6 | Feb 16 | Feb 23 |
| 16°F48% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 24 | Sep 30 | Oct 2 | Oct 5 | Oct 8 | Oct 13 | Oct 16 | Oct 21 | Oct 30 |
| 32°F | Oct 6 | Oct 13 | Oct 18 | Oct 22 | Oct 26 | Oct 30 | Nov 3 | Nov 7 | Nov 14 |
| 28°F | Oct 23 | Oct 29 | Nov 2 | Nov 7 | Nov 11 | Nov 16 | Nov 21 | Nov 27 | Dec 5 |
| 24°F99% of yrs | Nov 6 | Nov 13 | Nov 19 | Nov 25 | Nov 30 | Dec 5 | Dec 11 | Dec 19 | Jan 1 |
| 20°F85% of yrs | Nov 16 | Nov 27 | Dec 2 | Dec 8 | Dec 15 | Dec 22 | Dec 29 | Jan 6 | Jan 25 |
| 16°F48% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Forest Grove, 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 97116 →Compare Forest Grove with another place →
Weather by month in Forest Grove
August is the warmest month at Forest Grove, OR, averaging 82°F by day and 54°F at night; December is the coldest at 44°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 78% of years and May still brings one in 17% of years.
Warmth for growing adds up to 2,256 growing degree days a year (base 50°F), more than at 50% of the 103 Oregon stations. 29% of them (651) have built up by the end of June, and August adds the most, 553. Precipitation totals 46.6 inches a year, most in December (8.7") and least in July (0.3"); May to September bring 12% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 45 | 33 | 7.2 | 100% | 13 | 1 |
| Feb | 49 | 33 | 5.8 | 100% | 12 | 2 |
| Mar | 55 | 36 | 5.0 | 99% | 8 | 17 |
| Apr | 60 | 39 | 3.3 | 78% | 3 | 66 |
| May | 68 | 45 | 2.2 | 17% | <1 | 222 |
| Jun | 73 | 50 | 1.4 | 0% | 0 | 343 |
| Jul | 81 | 54 | 0.3 | 0% | 0 | 546 |
| Aug | 82 | 54 | 0.5 | 0% | 0 | 553 |
| Sep | 76 | 49 | 1.3 | 2% | 0 | 373 |
| Oct | 63 | 42 | 3.7 | 62% | 2 | 119 |
| Nov | 51 | 36 | 7.2 | 98% | 9 | 12 |
| Dec | 44 | 33 | 8.7 | 100% | 13 | 2 |
Monthly normals 1991–2020 at Forest Grove, OR (180 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, Portland-Hillsboro Airport, OR, 9 miles east of Forest Grove, has the same 50% last-frost date, a first frost 3 days earlier (October 23), a season 1 day shorter.
When it snows in Forest Grove, 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, 1.8 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 97116
| 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 August 3 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by October 12 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 26 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 97116 is 2 miles from Forest Grove, OR, which stands at 180 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 3 other ZIP codes share the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 97116 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.