Treasure County climate

Treasure County Frost Dates and Growing Season

NOAA 1991-2020 normals for Hysham, 9.2 km from Treasure County, elevation 2669 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Hysham. 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 10 and the first fall freeze around September 29, a growing season of about 141 days.

Median at 36°F
last May 21, first September 20
Median at 32°F
last May 10, first September 29
Median at 28°F
last April 30, first October 7

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

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 7Sep 11Sep 15Sep 18Sep 20Sep 22Sep 24Sep 27Oct 2
32°FSep 15Sep 21Sep 24Sep 27Sep 29Oct 1Oct 4Oct 6Oct 11
28°FSep 24Sep 29Oct 2Oct 4Oct 7Oct 11Oct 14Oct 17Oct 21
24°FOct 1Oct 6Oct 11Oct 15Oct 18Oct 21Oct 25Oct 28Nov 1
20°FOct 12Oct 18Oct 22Oct 26Oct 30Nov 1Nov 3Nov 7Nov 13
16°FOct 22Oct 28Nov 1Nov 3Nov 6Nov 9Nov 13Nov 18Nov 23

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°F138132128124121117113109102
32°F158153148145141138134129124
28°F182174168164161157153148140
24°F205198191186182178173167159
20°F228218212208204199193187179
16°F249240235229224218213208200

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
7,011
Cooling degree days, base 65°F
573
Growing degree days, base 40°F
4,533
Growing degree days, base 45°F
3,430
Growing degree days, base 50°F
2,490
Growing degree days, base 55°F
1,705
Growing degree days, base 60°F
1,067

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,28500
February1,06402
March863013
April548157
May28814222
June7480457
July11245699
August24196637
September17537324
October550273
November90306
December1,22600

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 9.2 km from Treasure 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 USC00244358 (Hysham). Public domain.