Frost dates / Washington / Sammamish

Frost dates in Sammamish, WA

The station on this page is SNOQUALMIE FALLS, WA US (USC00457773), 10.1 miles from the city point. Population in the Census 2024 estimate is 66,474.

Zone 8bUSDA average annual extreme minimum 15°F to 20°F, from ZIP 98075 (0.6 miles from the city point used on this page).

Median last 32°F is March 30. Median first 32°F is November 7. The 50% growing-season length is 223 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 4	Earlier date. A last 32°F on or after this day is common.
50%	March 30	Median.
10%	April 21	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 22	Earlier date. A first 32°F on or before this day is uncommon.
50%	November 7	Median.
90%	December 1	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%	252
50%	223
90%	195

28°F threshold

	10%	50%	90%
Last, on or after	March 25	February 27	January 16
First, on or before	November 6	November 29	December 31
Season at least	319 days	277 days	236 days

36°F threshold

	10%	50%	90%
Last, on or after	May 13	April 26	April 8
First, on or before	October 4	October 22	November 7
Season at least	206 days	180 days	156 days

Station SNOQUALMIE FALLS, WA US (USC00457773). Completeness flag R, 18 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 134.1 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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Sammamish, WA

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

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

Washington. Nearest qualified station: SNOQUALMIE FALLS, WA US (USC00457773), 10.1 miles. Median last 32°F March 30. Median first 32°F November 7. The 50% growing-season length is 223 days.

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32°F probabilities at this station

	10%	50%	90%
Last 32°F on or after	April 21	March 30	March 4
First 32°F on or before	October 22	November 7	December 1

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 Washington 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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