Ankeny climate

Ankeny Frost Dates and Growing Season

NOAA 1991-2020 normals for Ankeny, 3.7 km from Ankeny, elevation 975 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Ankeny. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

The last spring freeze typically comes around April 23 and the first fall freeze around October 15, a growing season of about 173 days.

Median at 36°F
last May 3, first October 4
Median at 32°F
last April 23, first October 15
Median at 28°F
last April 13, first October 25

Last freeze in spring

The chance of a later freeze than the date shown. At 10 percent, one spring in ten still freezes after the date; planting after the 10 percent date for 32°F is the cautious choice.

Threshold10%20%30%40%50%60%70%80%90%
36°FMay 16May 11May 7May 5May 3Apr 30Apr 27Apr 24Apr 19
32°FMay 6May 2Apr 29Apr 25Apr 23Apr 19Apr 16Apr 13Apr 8
28°FApr 27Apr 23Apr 19Apr 15Apr 13Apr 10Apr 7Apr 3Mar 31
24°FApr 19Apr 13Apr 9Apr 6Apr 3Mar 31Mar 28Mar 23Mar 17
20°FApr 9Apr 2Mar 30Mar 27Mar 23Mar 20Mar 16Mar 11Mar 6
16°FMar 30Mar 23Mar 19Mar 15Mar 12Mar 9Mar 6Mar 3Feb 28

First freeze in fall

The chance of an earlier freeze than the date shown. At 10 percent, one fall in ten freezes before the date.

Threshold10%20%30%40%50%60%70%80%90%
36°FSep 21Sep 26Sep 29Oct 2Oct 4Oct 7Oct 10Oct 13Oct 18
32°FSep 30Oct 5Oct 9Oct 12Oct 15Oct 18Oct 20Oct 23Oct 28
28°FOct 11Oct 17Oct 20Oct 23Oct 25Oct 27Oct 29Nov 1Nov 5
24°FOct 20Oct 24Oct 28Oct 31Nov 1Nov 4Nov 8Nov 11Nov 17
20°FOct 30Nov 2Nov 5Nov 8Nov 11Nov 15Nov 19Nov 23Nov 29
16°FNov 5Nov 10Nov 15Nov 18Nov 22Nov 25Nov 29Dec 3Dec 8

Growing season length

Days between the last spring and first fall freeze at each threshold, with the chance of a season at least that long.

Threshold10%20%30%40%50%60%70%80%90%
36°F173167162158155151147143136
32°F193186181178173169165160154
28°F214206200197193189185180173
24°F234227221216213208204198190
20°F256247243238233229224217211
16°F276267262257252248244239230

How often it gets that cold

The share of years with at least one night at or below each temperature.

36°F or colder
100% of years
32°F or colder
100% of years
28°F or colder
100% of years
24°F or colder
100% of years
20°F or colder
100% of years
16°F or colder
100% of years

Degree days

A degree day is one degree of the daily mean temperature beyond a base, for one day. Heating degree days count cold (the fuel a house burns), cooling degree days heat, growing degree days the warmth a crop needs; each crop has its own base.

Heating degree days, base 65°F
6,547
Cooling degree days, base 65°F
958
Growing degree days, base 40°F
5,397
Growing degree days, base 45°F
4,270
Growing degree days, base 50°F
3,262
Growing degree days, base 55°F
2,371
Growing degree days, base 60°F
1,600

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,37600
February1,11702
March857129
April4717114
May18059357
June20209639
July3319781
August8247704
September103103454
October41413159
November800023
December1,19801

What this means

NOAA computes these from the daily lows at the station over 1991-2020, fitting the dates of each year's last and first freeze to a distribution, so a date can be stated at any level of risk. 36°F is a frost risk for tender plants on a clear, calm night, since the ground cools below the air above it; 32°F is a freeze; 28°F is a hard freeze that kills most annuals.

The station is 3.7 km from Ankeny. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

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Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00130241 (Ankeny). Public domain.