Musselshell County climate

Musselshell County Frost Dates and Growing Season

NOAA 1991-2020 normals for Roundup, 12.2 km from Musselshell County, elevation 3200 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Roundup. 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 20 and the first fall freeze around September 21, a growing season of about 124 days.

Median at 36°F
last June 2, first September 10
Median at 32°F
last May 20, first September 21
Median at 28°F
last May 7, first October 1

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

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 24Aug 31Sep 4Sep 7Sep 10Sep 12Sep 15Sep 19Sep 23
32°FSep 5Sep 10Sep 14Sep 18Sep 21Sep 24Sep 26Sep 30Oct 4
28°FSep 18Sep 23Sep 26Sep 29Oct 1Oct 4Oct 6Oct 10Oct 15
24°FSep 26Oct 2Oct 5Oct 9Oct 13Oct 16Oct 19Oct 22Oct 25
20°FOct 7Oct 13Oct 16Oct 20Oct 23Oct 26Oct 29Nov 1Nov 6
16°FOct 15Oct 21Oct 25Oct 29Nov 1Nov 3Nov 7Nov 10Nov 17

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°F1171111061029894908476
32°F142136131128124120115110101
28°F165158154151146143139134127
24°F190183178173169165161156150
20°F213205200195190186182176167
16°F238229222217212207202195188

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
7,193
Cooling degree days, base 65°F
482
Growing degree days, base 40°F
4,225
Growing degree days, base 45°F
3,156
Growing degree days, base 50°F
2,260
Growing degree days, base 55°F
1,520
Growing degree days, base 60°F
926

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,23500
February1,04201
March88808
April602039
May3428177
June11152394
July20212657
August34174605
September19636306
October581166
November92405
December1,21800

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 12.2 km from Musselshell 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 USC00247214 (Roundup). Public domain.