Boswell climate

Boswell Frost Dates and Growing Season

NOAA 1991-2020 normals for Boswell 4WNW, 6.5 km from Boswell, elevation 772 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Boswell 4WNW. 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 25 and the first fall freeze around October 13, a growing season of about 169 days.

Median at 36°F
last May 5, first October 3
Median at 32°F
last April 25, first October 13
Median at 28°F
last April 15, first October 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°FMay 22May 16May 12May 9May 5May 3Apr 30Apr 26Apr 22
32°FMay 12May 5May 2Apr 28Apr 25Apr 22Apr 20Apr 17Apr 13
28°FApr 29Apr 23Apr 21Apr 18Apr 15Apr 12Apr 9Apr 6Apr 3
24°FApr 18Apr 14Apr 10Apr 7Apr 5Apr 3Apr 1Mar 28Mar 22
20°FApr 10Apr 5Apr 2Mar 31Mar 27Mar 23Mar 19Mar 14Mar 10
16°FApr 3Mar 29Mar 24Mar 19Mar 16Mar 13Mar 9Mar 4Feb 27

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 20Sep 25Sep 28Oct 1Oct 3Oct 5Oct 8Oct 11Oct 14
32°FSep 27Oct 3Oct 7Oct 10Oct 13Oct 15Oct 18Oct 21Oct 25
28°FOct 7Oct 13Oct 16Oct 19Oct 22Oct 25Oct 28Oct 31Nov 4
24°FOct 22Oct 26Oct 29Nov 1Nov 3Nov 6Nov 9Nov 13Nov 20
20°FNov 1Nov 5Nov 9Nov 12Nov 16Nov 19Nov 23Nov 27Dec 2
16°FNov 8Nov 14Nov 19Nov 23Nov 26Nov 30Dec 2Dec 6Dec 13

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°F167161157152149145141136129
32°F188182177173169165160155147
28°F211203198194190186182176169
24°F234227222217213208203199190
20°F259252245240236231226220212
16°F282273266260256251246240230

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
6,285
Cooling degree days, base 65°F
768
Growing degree days, base 40°F
5,224
Growing degree days, base 45°F
4,081
Growing degree days, base 50°F
3,061
Growing degree days, base 55°F
2,160
Growing degree days, base 60°F
1,391

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,28601
February1,06002
March848025
April4748116
May18063360
June31185604
July6235694
August13182634
September10482433
October40013161
November761028
December1,12404

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 6.5 km from Boswell. 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 USC00120858 (Boswell 4WNW). Public domain.