Purcell climate

Purcell Frost Dates and Growing Season

NOAA 1991-2020 normals for Purcell 2 Sw, 3.8 km from Purcell, elevation 1120 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Purcell 2 Sw. 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 4 and the first fall freeze around November 2, a growing season of about 210 days.

Median at 36°F
last April 17, first October 24
Median at 32°F
last April 4, first November 2
Median at 28°F
last March 23, 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°FMay 4Apr 28Apr 24Apr 20Apr 17Apr 13Apr 9Apr 5Mar 31
32°FApr 24Apr 18Apr 11Apr 7Apr 4Apr 2Mar 29Mar 25Mar 18
28°FApr 10Apr 4Mar 31Mar 27Mar 23Mar 20Mar 15Mar 11Mar 3
24°FMar 30Mar 23Mar 17Mar 14Mar 10Mar 6Mar 2Feb 27Feb 21
20°FMar 17Mar 12Mar 7Mar 3Feb 28Feb 24Feb 19Feb 11Feb 3
16°FMar 10Mar 3Feb 27Feb 21Feb 14Feb 9Feb 4Jan 29Jan 20

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 8Oct 14Oct 19Oct 21Oct 24Oct 27Oct 30Nov 2Nov 6
32°FOct 18Oct 24Oct 28Oct 31Nov 2Nov 5Nov 7Nov 11Nov 18
28°FOct 25Oct 31Nov 4Nov 7Nov 11Nov 14Nov 17Nov 21Nov 27
24°FNov 1Nov 7Nov 13Nov 17Nov 21Nov 25Nov 30Dec 3Dec 8
20°FNov 10Nov 19Nov 25Nov 29Dec 2Dec 5Dec 10Dec 15Dec 24
16°FNov 23Dec 1Dec 5Dec 11Dec 16Dec 22Dec 27Jan 2Jan 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°F211203198194189185181176168
32°F234226220215210206201195187
28°F255248242236231226221215207
24°F280270264259254248243235224
20°F306297288283277271266259250
16°F335325317310303297290282271

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
99% 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
3,295
Cooling degree days, base 65°F
2,003
Growing degree days, base 40°F
8,146
Growing degree days, base 45°F
6,620
Growing degree days, base 50°F
5,246
Growing degree days, base 55°F
4,021
Growing degree days, base 60°F
2,938

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January798015
February584143
March39213177
April17445334
May37161589
June1380829
July05381,002
August0504968
September15275709
October13477418
November4368130
December722031

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 Purcell. 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 USC00347327 (Purcell 2 Sw). Public domain.