Gilman climate

Gilman Frost Dates and Growing Season

NOAA 1991-2020 normals for Grinnell 3 Sw, 18 km from Gilman, elevation 905 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Grinnell 3 Sw. 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 6, a growing season of about 155 days.

Median at 36°F
last May 13, first September 27
Median at 32°F
last May 3, first October 6
Median at 28°F
last April 23, 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 27May 23May 19May 16May 13May 11May 7May 4Apr 30
32°FMay 17May 13May 8May 6May 3May 1Apr 27Apr 24Apr 19
28°FMay 9May 4Apr 30Apr 27Apr 23Apr 20Apr 17Apr 14Apr 9
24°FApr 30Apr 24Apr 20Apr 15Apr 11Apr 9Apr 7Apr 3Mar 30
20°FApr 19Apr 12Apr 8Apr 5Apr 2Mar 31Mar 27Mar 22Mar 14
16°FApr 8Apr 1Mar 29Mar 25Mar 22Mar 18Mar 15Mar 9Mar 3

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 18Sep 22Sep 25Sep 27Sep 30Oct 2Oct 5Oct 10
32°FSep 22Sep 27Sep 30Oct 3Oct 6Oct 9Oct 12Oct 15Oct 20
28°FOct 1Oct 7Oct 11Oct 14Oct 17Oct 19Oct 22Oct 25Oct 29
24°FOct 11Oct 17Oct 20Oct 23Oct 26Oct 28Oct 30Nov 2Nov 6
20°FOct 21Oct 27Oct 30Nov 1Nov 3Nov 6Nov 9Nov 13Nov 18
16°FNov 1Nov 4Nov 7Nov 10Nov 14Nov 17Nov 21Nov 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°F155149144140136133129124118
32°F175167163159155151147142136
28°F195189183179175170165161152
24°F215208202199194191186180172
20°F239231225220216211206201192
16°F262253247241236232226220213

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
7,038
Cooling degree days, base 65°F
692
Growing degree days, base 40°F
4,846
Growing degree days, base 45°F
3,763
Growing degree days, base 50°F
2,803
Growing degree days, base 55°F
1,968
Growing degree days, base 60°F
1,260

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,41800
February1,16801
March918120
April536381
May23837286
June40149560
July7242699
August20181626
September14071388
October4669126
November852016
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 18 km from Gilman. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00133473 (Grinnell 3 Sw). Public domain.