Sheridan County climate

Sheridan County Frost Dates and Growing Season

NOAA 1991-2020 normals for Plentywood, 7.5 km from Sheridan County, elevation 2048 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Plentywood. 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 25 and the first fall freeze around September 14, a growing season of about 111 days.

Median at 36°F
last June 6, first September 4
Median at 32°F
last May 25, first September 14
Median at 28°F
last May 15, first September 22

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

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

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°F10810196928883787161
32°F12812311811511110710410093
28°F146140136132129125122117111
24°F166158154150146142139134128
20°F186179173168163158155149142
16°F207200195190185180175169161

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
9,573
Cooling degree days, base 65°F
296
Growing degree days, base 40°F
3,468
Growing degree days, base 45°F
2,573
Growing degree days, base 50°F
1,803
Growing degree days, base 55°F
1,152
Growing degree days, base 60°F
646

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,72400
February1,42100
March1,18402
April738022
May4096146
June14938344
July48116533
August70115511
September30021214
October745132
November1,18101
December1,60600

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 7.5 km from Sheridan 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 USC00246586 (Plentywood). Public domain.