Williamson climate

Williamson Frost Dates and Growing Season

NOAA 1991-2020 normals for Prescott Love Fld, 11.8 km from Williamson, elevation 5042 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Prescott Love Fld. 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 20 and the first fall freeze around October 27, a growing season of about 188 days.

Median at 36°F
last May 4, first October 16
Median at 32°F
last April 20, first October 27
Median at 28°F
last April 1, first November 8

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 21May 15May 11May 7May 4May 1Apr 28Apr 25Apr 20
32°FMay 7May 1Apr 28Apr 25Apr 20Apr 16Apr 13Apr 8Apr 4
28°FApr 19Apr 12Apr 8Apr 5Apr 1Mar 28Mar 23Mar 18Mar 11
24°FApr 2Mar 26Mar 19Mar 13Mar 9Mar 4Feb 28Feb 23Feb 15
20°FMar 9Mar 2Feb 25Feb 20Feb 15Feb 10Feb 4Jan 30Jan 19
16°FFeb 21Feb 11Feb 5Jan 31Jan 24Jan 18Jan 10Jan 2Dec 23

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

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°F181176171166162158154149143
32°F209202197193188184179174165
28°F244234228223217212207200193
24°F280271264258253247242235225
20°F317306298292286280274267257
16°F357346338331324317309300289

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
95% 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
4,056
Cooling degree days, base 65°F
1,068
Growing degree days, base 40°F
6,393
Growing degree days, base 45°F
4,934
Growing degree days, base 50°F
3,694
Growing degree days, base 55°F
2,650
Growing degree days, base 60°F
1,781

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January78301
February63708
March533050
April3451145
May13845378
June14216653
July0357821
August1303767
September25138563
October2349258
November537050
December81101

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 11.8 km from Williamson. 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 USW00023184 (Prescott Love Fld). Public domain.