Four Corners climate

Four Corners Frost Dates and Growing Season

NOAA 1991-2020 normals for Bozeman 6 W Exp Farm, 2.8 km from Four Corners, elevation 4775 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Bozeman 6 W Exp Farm. 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 23 and the first fall freeze around September 23, a growing season of about 123 days.

Median at 36°F
last June 13, first September 9
Median at 32°F
last May 23, first September 23
Median at 28°F
last May 2, first October 3

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

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°F11110297928782787163
32°F14413813312812311811210596
28°F171165160156153149144139131
24°F199190185180175172167160154
20°F221213208203199194188181173
16°F242233227222218213208201193

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
7,708
Cooling degree days, base 65°F
230
Growing degree days, base 40°F
3,583
Growing degree days, base 45°F
2,581
Growing degree days, base 50°F
1,751
Growing degree days, base 55°F
1,084
Growing degree days, base 60°F
576

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,24500
February1,06500
March91204
April654026
May4092129
June20418274
July48103521
August6089496
September24917244
October616154
November97705
December1,27100

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 2.8 km from Four Corners. 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 USC00241047 (Bozeman 6 W Exp Farm). Public domain.