Miles City climate

Miles City Frost Dates and Growing Season

NOAA 1991-2020 normals for Miles City F Wiley Fld, 3.8 km from Miles City, elevation 2624 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Miles City F Wiley Fld. 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 8 and the first fall freeze around September 30, a growing season of about 144 days.

Median at 36°F
last May 18, first September 23
Median at 32°F
last May 8, first September 30
Median at 28°F
last April 29, first October 8

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

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 10Sep 14Sep 18Sep 21Sep 23Sep 26Sep 28Oct 1Oct 4
32°FSep 17Sep 22Sep 26Sep 28Sep 30Oct 2Oct 5Oct 9Oct 14
28°FSep 25Sep 29Oct 1Oct 5Oct 8Oct 12Oct 15Oct 18Oct 23
24°FOct 1Oct 7Oct 11Oct 15Oct 18Oct 21Oct 24Oct 27Oct 31
20°FOct 11Oct 17Oct 22Oct 25Oct 28Oct 31Nov 3Nov 6Nov 12
16°FOct 23Oct 28Nov 1Nov 3Nov 6Nov 9Nov 13Nov 17Nov 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°F143137132128124121117113106
32°F162156151148144140137132126
28°F183176171167163159155150143
24°F204196191187183179174168161
20°F226218211207202197193187179
16°F247238233227222217212207197

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
7,566
Cooling degree days, base 65°F
731
Growing degree days, base 40°F
4,566
Growing degree days, base 45°F
3,530
Growing degree days, base 50°F
2,630
Growing degree days, base 55°F
1,865
Growing degree days, base 60°F
1,233

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,41000
February1,15901
March941010
April586155
May31015213
June8197468
July10294748
August24256698
September17664354
October581478
November96806
December1,32000

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 3.8 km from Miles City. 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 USW00024037 (Miles City F Wiley Fld). Public domain.