Decorah climate

Decorah Frost Dates and Growing Season

NOAA 1991-2020 normals for Decorah, 0.8 km from Decorah, elevation 860 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Decorah. 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 May 3 and the first fall freeze around October 7, a growing season of about 157 days.

Median at 36°F
last May 13, first September 28
Median at 32°F
last May 3, first October 7
Median at 28°F
last April 22, first October 17

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 26May 22May 18May 15May 13May 10May 7May 3Apr 29
32°FMay 16May 12May 9May 5May 3Apr 30Apr 28Apr 24Apr 19
28°FMay 8May 2Apr 29Apr 26Apr 22Apr 19Apr 15Apr 12Apr 7
24°FApr 27Apr 21Apr 16Apr 12Apr 9Apr 6Apr 3Apr 1Mar 27
20°FApr 15Apr 7Apr 4Apr 2Mar 31Mar 29Mar 24Mar 20Mar 14
16°FApr 4Mar 31Mar 28Mar 24Mar 21Mar 17Mar 14Mar 10Mar 6

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 15Sep 19Sep 23Sep 25Sep 28Sep 30Oct 3Oct 6Oct 10
32°FSep 25Sep 29Oct 1Oct 4Oct 7Oct 9Oct 12Oct 15Oct 21
28°FOct 3Oct 9Oct 12Oct 15Oct 17Oct 20Oct 22Oct 26Oct 31
24°FOct 16Oct 20Oct 23Oct 26Oct 28Oct 31Nov 2Nov 5Nov 11
20°FOct 26Oct 31Nov 2Nov 4Nov 6Nov 10Nov 13Nov 17Nov 23
16°FNov 4Nov 7Nov 10Nov 13Nov 17Nov 20Nov 24Nov 27Dec 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°F156150146142138135131127120
32°F177170165161157154150145139
28°F200192187182178174170165157
24°F220214209205200196191186179
20°F244236230226222218214208200
16°F263255250246241237233228221

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
6,795
Cooling degree days, base 65°F
828
Growing degree days, base 40°F
5,165
Growing degree days, base 45°F
4,062
Growing degree days, base 50°F
3,070
Growing degree days, base 55°F
2,197
Growing degree days, base 60°F
1,446

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,42400
February1,16500
March899121
April4787106
May19352336
June28178600
July4268728
August11218673
September11192435
October42112151
November825020
December1,23501

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 0.8 km from Decorah. 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 USC00132110 (Decorah). Public domain.