Sloan climate

Sloan Frost Dates and Growing Season

NOAA 1991-2020 normals for Onawa 3NW, 20 km from Sloan, elevation 1060 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Onawa 3NW. 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 1 and the first fall freeze around October 3, a growing season of about 154 days.

Median at 36°F
last May 9, first September 25
Median at 32°F
last May 1, first October 3
Median at 28°F
last April 22, first October 13

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 22May 17May 14May 12May 9May 7May 4May 1Apr 28
32°FMay 13May 9May 6May 3May 1Apr 30Apr 27Apr 23Apr 19
28°FMay 6May 2Apr 29Apr 26Apr 22Apr 20Apr 17Apr 13Apr 9
24°FApr 27Apr 23Apr 19Apr 16Apr 13Apr 10Apr 7Apr 4Mar 31
20°FApr 19Apr 15Apr 10Apr 7Apr 5Apr 2Mar 31Mar 26Mar 19
16°FApr 12Apr 5Apr 1Mar 30Mar 26Mar 23Mar 19Mar 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 13Sep 17Sep 20Sep 22Sep 25Sep 28Oct 1Oct 3Oct 8
32°FSep 21Sep 25Sep 28Sep 30Oct 3Oct 6Oct 9Oct 13Oct 18
28°FSep 27Oct 1Oct 6Oct 9Oct 13Oct 17Oct 19Oct 22Oct 26
24°FOct 6Oct 12Oct 17Oct 20Oct 23Oct 25Oct 28Oct 31Nov 3
20°FOct 18Oct 23Oct 27Oct 30Nov 1Nov 3Nov 5Nov 9Nov 15
16°FOct 26Oct 31Nov 3Nov 6Nov 8Nov 11Nov 14Nov 19Nov 26

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°F156150146142138135131127121
32°F172166161157154151147142135
28°F192186180176172169165161153
24°F211204199195191188184178172
20°F230224218214210205201196190
16°F250242236232227223217212205

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
6,845
Cooling degree days, base 65°F
876
Growing degree days, base 40°F
5,208
Growing degree days, base 45°F
4,108
Growing degree days, base 50°F
3,119
Growing degree days, base 55°F
2,246
Growing degree days, base 60°F
1,497

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,41500
February1,14601
March873021
April4956101
May19057346
June21203631
July4292753
August13216668
September11590431
October43512151
November866016
December1,27200

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 20 km from Sloan. 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 USC00136243 (Onawa 3NW). Public domain.