Grimes climate

Grimes Frost Dates and Growing Season

NOAA 1991-2020 normals for Des Moines Wsfo-Johnston, 7.8 km from Grimes, elevation 959 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Des Moines Wsfo-Johnston. 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 19 and the first fall freeze around October 18, a growing season of about 179 days.

Median at 36°F
last April 30, first October 7
Median at 32°F
last April 19, first October 18
Median at 28°F
last April 9, first October 27

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 13May 7May 5May 2Apr 30Apr 27Apr 23Apr 20Apr 15
32°FMay 3Apr 29Apr 25Apr 22Apr 19Apr 16Apr 13Apr 9Apr 5
28°FApr 23Apr 19Apr 15Apr 12Apr 9Apr 6Apr 3Apr 1Mar 25
24°FApr 16Apr 10Apr 7Apr 3Apr 1Mar 29Mar 25Mar 19Mar 13
20°FApr 7Apr 2Mar 29Mar 25Mar 21Mar 18Mar 14Mar 10Mar 5
16°FMar 30Mar 24Mar 19Mar 16Mar 13Mar 10Mar 6Mar 2Feb 25

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 23Sep 28Sep 30Oct 3Oct 7Oct 9Oct 13Oct 16Oct 21
32°FOct 1Oct 7Oct 12Oct 15Oct 18Oct 20Oct 23Oct 26Oct 30
28°FOct 14Oct 19Oct 22Oct 25Oct 27Oct 30Nov 1Nov 3Nov 9
24°FOct 21Oct 27Oct 30Nov 1Nov 4Nov 6Nov 9Nov 13Nov 19
20°FOct 30Nov 3Nov 6Nov 9Nov 12Nov 15Nov 19Nov 24Dec 1
16°FNov 6Nov 10Nov 14Nov 17Nov 21Nov 25Nov 30Dec 3Dec 11

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°F178171166163159156151147140
32°F198192187183179174170166159
28°F218211206202199195191186179
24°F237230225221217213209203195
20°F257249244239234231225220213
16°F276268262257253248243237228

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
6,317
Cooling degree days, base 65°F
988
Growing degree days, base 40°F
5,549
Growing degree days, base 45°F
4,396
Growing degree days, base 50°F
3,361
Growing degree days, base 55°F
2,445
Growing degree days, base 60°F
1,650

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,34700
February1,08603
March817235
April4359134
May16263374
June17210643
July3317780
August6261721
September91111472
October39416172
November786027
December1,17501

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 7.8 km from Grimes. 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 USC00132209 (Des Moines Wsfo-Johnston). Public domain.