Boswell climate

Boswell Frost Dates and Growing Season

NOAA 1991-2020 normals for Laurel Summit, 9.6 km from Boswell, elevation 2730 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Laurel Summit. 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 6 and the first fall freeze around October 12, a growing season of about 159 days.

Median at 36°F
last May 16, first October 3
Median at 32°F
last May 6, first October 12
Median at 28°F
last April 27, first October 24

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 27May 24May 20May 16May 13May 9May 5Apr 30
32°FMay 23May 18May 13May 10May 6May 3Apr 30Apr 26Apr 22
28°FMay 15May 8May 3Apr 30Apr 27Apr 24Apr 21Apr 18Apr 14
24°FMay 4Apr 28Apr 22Apr 19Apr 17Apr 14Apr 11Apr 8Apr 3
20°FApr 20Apr 15Apr 12Apr 8Apr 6Apr 4Apr 1Mar 30Mar 23
16°FApr 10Apr 5Apr 1Mar 31Mar 28Mar 25Mar 22Mar 18Mar 11

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 21Sep 25Sep 28Oct 1Oct 3Oct 5Oct 7Oct 11Oct 15
32°FOct 1Oct 4Oct 7Oct 10Oct 12Oct 15Oct 18Oct 22Oct 26
28°FOct 10Oct 14Oct 18Oct 21Oct 24Oct 26Oct 30Nov 1Nov 5
24°FOct 21Oct 26Oct 30Nov 1Nov 3Nov 5Nov 9Nov 12Nov 17
20°FNov 1Nov 4Nov 7Nov 10Nov 13Nov 15Nov 18Nov 23Dec 1
16°FNov 8Nov 12Nov 16Nov 19Nov 24Nov 28Dec 1Dec 5Dec 12

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°F160153147142138134129125119
32°F180172168163159155150145137
28°F198192188182179175170164157
24°F220213208204200195190185176
20°F243236230226221217213208200
16°F264255250245241237233228221

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
7,281
Cooling degree days, base 65°F
229
Growing degree days, base 40°F
4,026
Growing degree days, base 45°F
2,960
Growing degree days, base 50°F
2,036
Growing degree days, base 55°F
1,258
Growing degree days, base 60°F
642

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,31301
February1,12602
March1,001012
April600368
May33112196
June11938372
July4284507
August5665474
September19324292
October516394
November827017
December1,15802

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 9.6 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 USC00364839 (Laurel Summit). Public domain.