Fremont County climate

Fremont County Frost Dates and Growing Season

NOAA 1991-2020 normals for Ashton 1N, 17.7 km from Fremont County, elevation 5212 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Ashton 1N. 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 21 and the first fall freeze around September 21, a growing season of about 121 days.

Median at 36°F
last June 10, first September 7
Median at 32°F
last May 21, first September 21
Median at 28°F
last May 3, 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°FJul 2Jun 24Jun 19Jun 14Jun 10Jun 7Jun 4May 30May 22
32°FJun 13Jun 7Jun 1May 27May 21May 18May 13May 9May 4
28°FMay 26May 15May 10May 6May 3Apr 30Apr 25Apr 21Apr 16
24°FMay 7Apr 30Apr 26Apr 22Apr 19Apr 15Apr 12Apr 8Apr 3
20°FApr 22Apr 17Apr 13Apr 9Apr 6Apr 3Mar 31Mar 27Mar 21
16°FApr 13Apr 7Apr 3Mar 31Mar 28Mar 23Mar 19Mar 13Mar 7

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°FAug 22Aug 29Sep 1Sep 4Sep 7Sep 10Sep 14Sep 18Sep 24
32°FSep 4Sep 9Sep 13Sep 18Sep 21Sep 25Sep 29Oct 3Oct 7
28°FSep 13Sep 22Sep 27Oct 1Oct 4Oct 7Oct 11Oct 15Oct 20
24°FSep 28Oct 4Oct 8Oct 13Oct 17Oct 21Oct 24Oct 28Nov 3
20°FOct 10Oct 18Oct 22Oct 25Oct 28Oct 31Nov 3Nov 8Nov 15
16°FOct 20Oct 26Oct 31Nov 3Nov 6Nov 10Nov 13Nov 18Nov 23

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°F11210497938883767062
32°F14513813112612111610910293
28°F176168163157152146140133123
24°F201193187182178172166160150
20°F225217210205200196191186177
16°F250240233227221216211205196

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
8,043
Cooling degree days, base 65°F
210
Growing degree days, base 40°F
3,493
Growing degree days, base 45°F
2,539
Growing degree days, base 50°F
1,730
Growing degree days, base 55°F
1,068
Growing degree days, base 60°F
553

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,35900
February1,12800
March98001
April672021
May3903138
June18921291
July4599519
August5776484
September24611238
October631037
November1,00801
December1,33600

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 17.7 km from Fremont 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 USC00100470 (Ashton 1N). Public domain.