Frost dates / Minnesota / Duluth

Frost dates in Duluth, MN

The station on this page is DULUTH HARBOR STN, MN US (USC00212246), 2.1 miles from the city point. Population in the Census 2024 estimate is 87,986.

Zone 4bUSDA average annual extreme minimum -25°F to -20°F, from ZIP 55806 (0.5 miles from the city point used on this page).

Median last 32°F is May 14. Median first 32°F is October 12. The 50% growing-season length is 149 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%	April 24	Earlier date. A last 32°F on or after this day is common.
50%	May 14	Median.
10%	June 1	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%	September 25	Earlier date. A first 32°F on or before this day is uncommon.
50%	October 12	Median.
90%	October 26	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%	175
50%	149
90%	124

28°F threshold

	10%	50%	90%
Last, on or after	May 18	April 29	April 11
First, on or before	October 9	October 25	November 7
Season at least	199 days	179 days	154 days

36°F threshold

	10%	50%	90%
Last, on or after	June 16	May 31	May 12
First, on or before	September 12	September 30	October 14
Season at least	145 days	121 days	98 days

Station DULUTH HARBOR STN, MN US (USC00212246). Completeness flag R, 14 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 185.9 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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Duluth, MN

Zone 4bAverage annual extreme minimum -25°F to -20°F

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

Minnesota. Nearest qualified station: DULUTH HARBOR STN, MN US (USC00212246), 2.1 miles. Median last 32°F May 14. Median first 32°F October 12. The 50% growing-season length is 149 days.

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32°F probabilities at this station

	10%	50%	90%
Last 32°F on or after	June 1	May 14	April 24
First 32°F on or before	September 25	October 12	October 26

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 Minnesota 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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