Gillette climate

Gillette Frost Dates and Growing Season

NOAA 1991-2020 normals for Gillette 4SE, 5 km from Gillette, elevation 4640 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Gillette 4SE. 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 15 and the first fall freeze around October 1, a growing season of about 136 days.

Median at 36°F
last May 28, first September 21
Median at 32°F
last May 15, first October 1
Median at 28°F
last May 2, first October 10

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

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°F13312712211811411010610194
32°F155149144140136133129125118
28°F178171167163159155151146139
24°F199192187183179174170166158
20°F221213208203198194189184178
16°F243236228222217211206200190

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
7,158
Cooling degree days, base 65°F
571
Growing degree days, base 40°F
4,348
Growing degree days, base 45°F
3,296
Growing degree days, base 50°F
2,398
Growing degree days, base 55°F
1,651
Growing degree days, base 60°F
1,039

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,20900
February1,05801
March876014
April629044
May36911173
June11472413
July19227672
August29201638
September18358347
October566284
November896013
December1,21000

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 5 km from Gillette. 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 USC00483855 (Gillette 4SE). Public domain.