Ackley climate

Ackley Frost Dates and Growing Season

NOAA 1991-2020 normals for Iowa Falls, 16.9 km from Ackley, elevation 1055 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Iowa Falls. 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 28 and the first fall freeze around October 10, a growing season of about 164 days.

Median at 36°F
last May 7, first September 30
Median at 32°F
last April 28, first October 10
Median at 28°F
last April 17, first October 20

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 20May 15May 12May 9May 7May 5May 3Apr 30Apr 25
32°FMay 11May 7May 3May 1Apr 28Apr 25Apr 22Apr 17Apr 13
28°FMay 1Apr 27Apr 24Apr 20Apr 17Apr 14Apr 11Apr 8Apr 3
24°FApr 22Apr 17Apr 13Apr 10Apr 7Apr 4Apr 1Mar 29Mar 22
20°FApr 14Apr 8Apr 4Apr 1Mar 29Mar 24Mar 20Mar 16Mar 11
16°FApr 5Mar 30Mar 25Mar 22Mar 19Mar 15Mar 12Mar 8Mar 4

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 17Sep 22Sep 25Sep 28Sep 30Oct 3Oct 6Oct 9Oct 13
32°FSep 26Oct 1Oct 4Oct 7Oct 10Oct 13Oct 15Oct 18Oct 22
28°FOct 5Oct 12Oct 15Oct 18Oct 20Oct 23Oct 25Oct 29Nov 2
24°FOct 17Oct 22Oct 25Oct 28Oct 30Nov 1Nov 4Nov 7Nov 11
20°FOct 28Nov 1Nov 3Nov 5Nov 8Nov 10Nov 14Nov 17Nov 23
16°FNov 4Nov 7Nov 11Nov 14Nov 17Nov 20Nov 24Nov 28Dec 2

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°F164158153150146143139135129
32°F183177173168164161156152147
28°F204197193188184180176172165
24°F225218213209205201197193186
20°F247238232228223219215210203
16°F263256251246241236232227220

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
7,307
Cooling degree days, base 65°F
693
Growing degree days, base 40°F
4,814
Growing degree days, base 45°F
3,754
Growing degree days, base 50°F
2,807
Growing degree days, base 55°F
1,979
Growing degree days, base 60°F
1,272

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,49100
February1,22200
March963013
April549375
May23139295
June32157575
July6240699
August16179628
September13768388
October4727122
November891013
December1,29600

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 16.9 km from Ackley. 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 USC00134142 (Iowa Falls). Public domain.