Hamilton County climate

Hamilton County Frost Dates and Growing Season

NOAA 1991-2020 normals for Webster City, 12 km from Hamilton County, elevation 1072 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Webster City. 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 2, a growing season of about 150 days.

Median at 36°F
last May 11, first September 23
Median at 32°F
last May 3, first October 2
Median at 28°F
last April 24, first October 12

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 24May 20May 17May 14May 11May 9May 6May 4Apr 30
32°FMay 16May 11May 8May 6May 3May 1Apr 29Apr 25Apr 20
28°FMay 7May 2Apr 30Apr 27Apr 24Apr 21Apr 18Apr 15Apr 10
24°FApr 28Apr 23Apr 20Apr 17Apr 14Apr 11Apr 8Apr 5Apr 1
20°FApr 20Apr 14Apr 11Apr 6Apr 4Apr 1Mar 30Mar 24Mar 17
16°FApr 11Apr 5Apr 1Mar 30Mar 27Mar 22Mar 18Mar 14Mar 8

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 10Sep 15Sep 18Sep 21Sep 23Sep 26Sep 29Oct 1Oct 5
32°FSep 18Sep 23Sep 27Sep 30Oct 2Oct 4Oct 7Oct 11Oct 16
28°FSep 27Oct 2Oct 5Oct 8Oct 12Oct 14Oct 18Oct 21Oct 25
24°FOct 8Oct 13Oct 17Oct 20Oct 22Oct 25Oct 27Oct 30Nov 3
20°FOct 19Oct 23Oct 26Oct 29Nov 1Nov 2Nov 5Nov 8Nov 14
16°FOct 28Nov 1Nov 3Nov 6Nov 9Nov 12Nov 15Nov 19Nov 25

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°F151146141136133129125121116
32°F169162157153150146143138131
28°F188181176173169165161156149
24°F207201197192188185181176169
20°F230221216211207203199194187
16°F250243238233229223218213206

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
7,457
Cooling degree days, base 65°F
618
Growing degree days, base 40°F
4,661
Growing degree days, base 45°F
3,613
Growing degree days, base 50°F
2,678
Growing degree days, base 55°F
1,862
Growing degree days, base 60°F
1,171

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,50200
February1,23600
March971013
April561371
May24135283
June39140550
July9220676
August24156597
September15359366
October4966112
November908011
December1,31700

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 12 km from Hamilton County. 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 USC00138806 (Webster City). Public domain.