Riverton climate

Riverton Frost Dates and Growing Season

NOAA 1991-2020 normals for Riverton, 0.8 km from Riverton, elevation 4955 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Riverton. 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 12 and the first fall freeze around September 24, a growing season of about 132 days.

Median at 36°F
last May 28, first September 14
Median at 32°F
last May 12, first September 24
Median at 28°F
last May 1, first October 4

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°FJun 10Jun 5Jun 3May 31May 28May 24May 20May 17May 12
32°FMay 26May 21May 18May 15May 12May 10May 7May 5May 1
28°FMay 16May 10May 7May 4May 1Apr 30Apr 27Apr 24Apr 20
24°FMay 5Apr 30Apr 27Apr 24Apr 21Apr 18Apr 16Apr 12Apr 7
20°FApr 25Apr 19Apr 16Apr 13Apr 9Apr 6Apr 3Mar 31Mar 23
16°FApr 14Apr 8Apr 3Mar 31Mar 27Mar 22Mar 18Mar 13Mar 9

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

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°F1251201161121091051019690
32°F151145140136132128124120114
28°F172166161158154150146139133
24°F194187182178174170166161155
20°F216209203198194190185180173
16°F238231224220215211205199192

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
8,101
Cooling degree days, base 65°F
467
Growing degree days, base 40°F
4,059
Growing degree days, base 45°F
3,068
Growing degree days, base 50°F
2,218
Growing degree days, base 55°F
1,503
Growing degree days, base 60°F
918

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,50500
February1,18900
March90905
April623037
May3559180
June10869416
July16212662
August30153588
September22024279
October627150
November1,05301
December1,46800

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 0.8 km from Riverton. 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 USC00487760 (Riverton). Public domain.