Boswell climate

Boswell Frost Dates and Growing Season

NOAA 1991-2020 normals for Antlers 5NW, 27 km from Boswell, elevation 578 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Antlers 5NW. 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 April 2 and the first fall freeze around November 1, a growing season of about 212 days.

Median at 36°F
last April 13, first October 22
Median at 32°F
last April 2, first November 1
Median at 28°F
last March 18, first November 11

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°FApr 29Apr 24Apr 20Apr 16Apr 13Apr 9Apr 6Apr 3Mar 29
32°FApr 20Apr 12Apr 8Apr 4Apr 2Mar 30Mar 26Mar 20Mar 14
28°FApr 4Mar 31Mar 26Mar 22Mar 18Mar 14Mar 11Mar 6Feb 28
24°FMar 24Mar 17Mar 13Mar 9Mar 6Mar 3Feb 28Feb 22Feb 11
20°FMar 12Mar 7Mar 3Feb 27Feb 22Feb 14Feb 6Jan 31Jan 23
16°FMar 5Feb 28Feb 18Feb 9Feb 3Jan 28Jan 22Jan 13Jan 1

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°FOct 9Oct 14Oct 17Oct 20Oct 22Oct 25Oct 28Oct 31Nov 5
32°FOct 17Oct 21Oct 25Oct 29Nov 1Nov 3Nov 6Nov 11Nov 17
28°FOct 26Nov 1Nov 4Nov 7Nov 11Nov 15Nov 19Nov 24Dec 1
24°FNov 5Nov 11Nov 16Nov 20Nov 24Nov 29Dec 2Dec 6Dec 14
20°FNov 17Nov 25Dec 1Dec 4Dec 8Dec 14Dec 22Dec 29Jan 4
16°FDec 1Dec 8Dec 13Dec 20Dec 29Jan 2Jan 7Jan 14Jan 25

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°F211205199195191187182177169
32°F236227222217212208203197189
28°F263254247242237232226220210
24°F295283275269262257252244235
20°F330318309301294287280272261
16°F363349340333325316308301289

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
90% 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
3,127
Cooling degree days, base 65°F
1,913
Growing degree days, base 40°F
8,144
Growing degree days, base 45°F
6,581
Growing degree days, base 50°F
5,175
Growing degree days, base 55°F
3,933
Growing degree days, base 60°F
2,846

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January738124
February552362
March37811174
April16438334
May38159586
June0360810
July0493958
August0496960
September11275714
October16170384
November4098136
December677135

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 27 km from Boswell. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00340257 (Antlers 5NW). Public domain.