Riley County climate

Riley County Frost Dates and Growing Season

NOAA 1991-2020 normals for Tuttle Creek Lake, 12.9 km from Riley County, elevation 1058 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Tuttle Creek Lake. 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 22 and the first fall freeze around October 20, a growing season of about 179 days.

Median at 36°F
last April 30, first October 8
Median at 32°F
last April 22, first October 20
Median at 28°F
last April 10, first October 28

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 14May 9May 5May 2Apr 30Apr 28Apr 26Apr 22Apr 17
32°FMay 5Apr 30Apr 27Apr 24Apr 22Apr 19Apr 16Apr 13Apr 8
28°FApr 26Apr 21Apr 17Apr 14Apr 10Apr 7Apr 5Apr 2Mar 28
24°FApr 17Apr 10Apr 6Apr 3Apr 1Mar 29Mar 25Mar 20Mar 14
20°FApr 6Apr 2Mar 29Mar 25Mar 20Mar 16Mar 12Mar 8Mar 3
16°FMar 30Mar 22Mar 18Mar 14Mar 10Mar 6Mar 2Feb 28Feb 22

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 25Sep 30Oct 2Oct 5Oct 8Oct 11Oct 14Oct 18Oct 22
32°FOct 4Oct 10Oct 14Oct 17Oct 20Oct 22Oct 24Oct 27Nov 1
28°FOct 15Oct 19Oct 22Oct 25Oct 28Oct 31Nov 2Nov 5Nov 10
24°FOct 23Oct 28Nov 1Nov 3Nov 5Nov 8Nov 12Nov 14Nov 20
20°FOct 31Nov 4Nov 7Nov 11Nov 14Nov 17Nov 21Nov 26Dec 1
16°FNov 6Nov 12Nov 16Nov 20Nov 24Nov 28Dec 1Dec 5Dec 10

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°F179174169165161157153148141
32°F198191187183179175171167160
28°F219211207203198194190185177
24°F241233226222218213209204196
20°F264256249243238233228223214
16°F284275268263259253247242233

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
5,426
Cooling degree days, base 65°F
1,317
Growing degree days, base 40°F
6,204
Growing degree days, base 45°F
4,966
Growing degree days, base 50°F
3,862
Growing degree days, base 55°F
2,885
Growing degree days, base 60°F
2,036

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,15601
February93006
March691358
April37116175
May13487424
June13268705
July1413877
August3353815
September68154537
October32623220
November690141
December1,04302

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 12.9 km from Riley 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 USC00148259 (Tuttle Creek Lake). Public domain.