Dunkerton climate

Dunkerton Frost Dates and Growing Season

NOAA 1991-2020 normals for Waterloo Muni AP, 19.8 km from Dunkerton, elevation 868 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Waterloo Muni AP. 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 27 and the first fall freeze around October 10, a growing season of about 165 days.

Median at 36°F
last May 6, first September 30
Median at 32°F
last April 27, first October 10
Median at 28°F
last April 16, 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 17May 14May 10May 8May 6May 3Apr 30Apr 28Apr 23
32°FMay 10May 5May 2Apr 30Apr 27Apr 24Apr 20Apr 16Apr 11
28°FMay 2Apr 27Apr 22Apr 19Apr 16Apr 13Apr 10Apr 7Apr 3
24°FApr 22Apr 17Apr 13Apr 9Apr 7Apr 4Apr 1Mar 29Mar 22
20°FApr 14Apr 8Apr 3Apr 1Mar 29Mar 25Mar 21Mar 16Mar 11
16°FApr 3Mar 30Mar 26Mar 21Mar 18Mar 15Mar 12Mar 8Mar 2

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 16Sep 20Sep 24Sep 27Sep 30Oct 2Oct 4Oct 7Oct 11
32°FSep 26Oct 1Oct 4Oct 7Oct 10Oct 12Oct 15Oct 18Oct 21
28°FOct 6Oct 11Oct 15Oct 18Oct 20Oct 22Oct 24Oct 27Oct 31
24°FOct 17Oct 21Oct 24Oct 27Oct 29Oct 31Nov 2Nov 5Nov 10
20°FOct 27Oct 30Nov 1Nov 4Nov 7Nov 9Nov 14Nov 18Nov 23
16°FNov 2Nov 6Nov 10Nov 13Nov 17Nov 19Nov 23Nov 26Dec 1

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°F166159155151147143139134129
32°F184178173168165161157153146
28°F204199194190185182178172165
24°F224218213209205201197191183
20°F248239233229224220215210202
16°F265257252248244238234229220

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
6,714
Cooling degree days, base 65°F
918
Growing degree days, base 40°F
5,303
Growing degree days, base 45°F
4,192
Growing degree days, base 50°F
3,194
Growing degree days, base 55°F
2,316
Growing degree days, base 60°F
1,553

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,41200
February1,15101
March879124
April4757107
May17364366
June18213645
July3297759
August10225680
September10997442
October42813149
November828020
December1,22901

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 19.8 km from Dunkerton. 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 USW00094910 (Waterloo Muni AP). Public domain.