Frost dates / Oregon / Hillsboro

Frost dates in Hillsboro, OR

The station on this page is PORTLAND-HILLSBORO AP, OR US (USW00094261), 1.1 miles from the city point. Population in the Census 2024 estimate is 110,337.

Zone 8bUSDA average annual extreme minimum 15°F to 20°F, from ZIP 97124 (3 miles from the city point used on this page).

Median last 32°F is April 16. Median first 32°F is October 23. The 50% growing-season length is 191 days. The green band runs from the median last frost to the median first frost. Thin ticks mark the 10%, 50%, and 90% dates.

Outside the median season Growing seasonTicks: 10%, 50%, and 90%

Last 32°F in spring

NCEI’s probability is the chance the last spring minimum of 32°F or lower occurs on or after the date.

Probability	Date	How to read it
90%	March 25	Earlier date. A last 32°F on or after this day is common.
50%	April 16	Median.
10%	May 3	Later date. A last 32°F on or after this day is uncommon.

First 32°F in fall

NCEI’s probability is the chance the first autumn minimum of 32°F or lower occurs on or before the date.

Probability	Date	How to read it
10%	October 3	Earlier date. A first 32°F on or before this day is uncommon.
50%	October 23	Median.
90%	November 18	Later date. A first 32°F on or before this day is common.

32°F growing-season length

Days between the last spring 32°F and the first autumn 32°F. The figure is a length the season meets or exceeds at that probability, from NCEI, not a subtraction done on this site.

Probability the season is at least this long	Days
10%	223
50%	191
90%	161

28°F threshold

	10%	50%	90%
Last, on or after	April 9	March 13	February 15
First, on or before	October 20	November 12	December 10
Season at least	286 days	243 days	208 days

36°F threshold

	10%	50%	90%
Last, on or after	May 27	May 5	April 21
First, on or before	September 20	October 6	October 31
Season at least	181 days	153 days	127 days

Station PORTLAND-HILLSBORO AP, OR US (USW00094261). Completeness flag R, 20 years used for the 32°F dates. NCEI’s annual probability of at least one day at or below 32°F is 100%. Freeze dates are conditional on that threshold occurring. Elevation 62.2 m. The same probability language applies to the 28°F and 36°F rows when those dates passed the same quality checks.

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Hillsboro, OR

Zone 8bAverage annual extreme minimum 15°F to 20°F

Outside the median season Growing seasonTicks: 10%, 50%, and 90%

Oregon. Nearest qualified station: PORTLAND-HILLSBORO AP, OR US (USW00094261), 1.1 miles. Median last 32°F April 16. Median first 32°F October 23. The 50% growing-season length is 191 days.

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32°F probabilities at this station

	10%	50%	90%
Last 32°F on or after	May 3	April 16	March 25
First 32°F on or before	October 3	October 23	November 18

Column order matches the NCEI file: for the last freeze, 10% is the later date and 90% is the earlier date. How to read the probabilities.

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Planting calendar

Frost dates for Oregon are above. Planting windows appear for states with a cited extension guide. The fall and seed tools use the numbers you enter and the station dates.

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