Fremont County climate

Fremont County Frost Dates and Growing Season

NOAA 1991-2020 normals for Riverton, 12.8 km from Fremont County, elevation 5568 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 16 and the first fall freeze around September 28, a growing season of about 133 days.

Median at 36°F
last May 30, first September 19
Median at 32°F
last May 16, first September 28
Median at 28°F
last May 3, first October 7

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

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°F1291231191141101071039891
32°F152146141137133129125120113
28°F173167162158154150146141133
24°F197191184179175171167161155
20°F218210205201197192188183176
16°F241233227221216211206200192

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
7,927
Cooling degree days, base 65°F
499
Growing degree days, base 40°F
4,073
Growing degree days, base 45°F
3,087
Growing degree days, base 50°F
2,248
Growing degree days, base 55°F
1,542
Growing degree days, base 60°F
959

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,41800
February1,15600
March91205
April647029
May3758165
June11567407
July10224678
August26169608
September20531302
October628154
November1,02801
December1,40700

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 12.8 km from Fremont County. 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 USW00024061 (Riverton). Public domain.