Frost dates / Iowa / Sioux City

Frost dates in Sioux City, IA

The station on this page is SIOUX CITY ANG, IA US (USC00137702), 6.9 miles from the city point. Population in the Census 2024 estimate is 86,875.

Zone 5aUSDA average annual extreme minimum -20°F to -15°F, from ZIP 51101 (0.3 miles from the city point used on this page).

Median last 32°F is April 29. Median first 32°F is October 7. The 50% growing-season length is 161 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 15	Earlier date. A last 32°F on or after this day is common.
50%	April 29	Median.
10%	May 11	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 24	Earlier date. A first 32°F on or before this day is uncommon.
50%	October 7	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%	178
50%	161
90%	143

28°F threshold

	10%	50%	90%
Last, on or after	May 2	April 19	April 5
First, on or before	October 2	October 18	October 30
Season at least	198 days	180 days	160 days

36°F threshold

	10%	50%	90%
Last, on or after	May 21	May 7	April 25
First, on or before	September 18	September 29	October 11
Season at least	160 days	144 days	125 days

Station SIOUX CITY ANG, IA US (USC00137702). Completeness flag R, 10 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 335.3 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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Sioux City, IA

Zone 5aAverage annual extreme minimum -20°F to -15°F

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

Iowa. Nearest qualified station: SIOUX CITY ANG, IA US (USC00137702), 6.9 miles. Median last 32°F April 29. Median first 32°F October 7. The 50% growing-season length is 161 days.

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32°F probabilities at this station

	10%	50%	90%
Last 32°F on or after	May 11	April 29	April 15
First 32°F on or before	September 24	October 7	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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