Frost dates / Iowa / Ames

Frost dates in Ames, IA

The station on this page is AMES MUNI AP, IA US (USW00094989), 2.4 miles from the city point. Population in the Census 2024 estimate is 69,026.

Zone 5bUSDA average annual extreme minimum -15°F to -10°F, from ZIP 50012 (1.5 miles from the city point used on this page).

Median last 32°F is April 26. Median first 32°F is October 8. The 50% growing-season length is 164 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 11	Earlier date. A last 32°F on or after this day is common.
50%	April 26	Median.
10%	May 9	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 23	Earlier date. A first 32°F on or before this day is uncommon.
50%	October 8	Median.
90%	October 21	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%	184
50%	164
90%	144

28°F threshold

	10%	50%	90%
Last, on or after	May 1	April 14	April 1
First, on or before	October 4	October 19	October 31
Season at least	205 days	184 days	164 days

36°F threshold

	10%	50%	90%
Last, on or after	May 17	May 5	April 21
First, on or before	September 15	September 28	October 11
Season at least	163 days	146 days	127 days

Station AMES MUNI AP, IA US (USW00094989). Completeness flag S, 24 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 283.5 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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Ames, IA

Zone 5bAverage annual extreme minimum -15°F to -10°F

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

Iowa. Nearest qualified station: AMES MUNI AP, IA US (USW00094989), 2.4 miles. Median last 32°F April 26. Median first 32°F October 8. The 50% growing-season length is 164 days.

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32°F probabilities at this station

	10%	50%	90%
Last 32°F on or after	May 9	April 26	April 11
First 32°F on or before	September 23	October 8	October 21

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 Iowa 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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