Boyd County climate

Boyd County Frost Dates and Growing Season

NOAA 1991-2020 normals for Butte, 7.1 km from Boyd County, elevation 1806 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Butte. 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 4 and the first fall freeze around October 6, a growing season of about 152 days.

Median at 36°F
last May 14, first September 28
Median at 32°F
last May 4, first October 6
Median at 28°F
last April 25, first October 15

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

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°F152146142138135132128124118
32°F171166160156152149145141135
28°F193186180176172168164159152
24°F211204199195192188183178170
20°F232224219214209205201196189
16°F251244238232228223218212205

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
7,109
Cooling degree days, base 65°F
778
Growing degree days, base 40°F
4,870
Growing degree days, base 45°F
3,795
Growing degree days, base 50°F
2,848
Growing degree days, base 55°F
2,030
Growing degree days, base 60°F
1,337

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,36100
February1,12801
March921018
April578268
May27232260
June50140540
July7286744
August17228676
September13584407
October4927119
November888014
December1,26000

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 7.1 km from Boyd 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 USC00251365 (Butte). Public domain.