Afton climate

Afton Frost Dates and Growing Season

NOAA 1991-2020 normals for Creston 2 Sw, 16.4 km from Afton, elevation 1296 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Creston 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 28 and the first fall freeze around October 11, a growing season of about 164 days.

Median at 36°F
last May 6, first October 1
Median at 32°F
last April 28, first October 11
Median at 28°F
last April 17, first October 23

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 19May 14May 10May 9May 6May 4May 2Apr 29Apr 23
32°FMay 9May 6May 3May 1Apr 28Apr 25Apr 22Apr 18Apr 14
28°FMay 2Apr 28Apr 23Apr 21Apr 17Apr 15Apr 12Apr 8Apr 5
24°FApr 23Apr 17Apr 14Apr 10Apr 8Apr 5Apr 2Mar 31Mar 25
20°FApr 15Apr 9Apr 6Apr 3Mar 31Mar 28Mar 24Mar 19Mar 11
16°FApr 7Apr 1Mar 29Mar 24Mar 20Mar 15Mar 12Mar 8Mar 4

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 16Sep 21Sep 25Sep 29Oct 1Oct 4Oct 7Oct 10Oct 15
32°FSep 24Sep 30Oct 4Oct 8Oct 11Oct 14Oct 17Oct 21Oct 26
28°FOct 5Oct 12Oct 16Oct 19Oct 23Oct 25Oct 27Oct 31Nov 4
24°FOct 17Oct 22Oct 25Oct 29Oct 31Nov 2Nov 4Nov 8Nov 13
20°FOct 25Oct 30Nov 1Nov 4Nov 7Nov 9Nov 12Nov 16Nov 22
16°FNov 1Nov 5Nov 8Nov 11Nov 14Nov 18Nov 21Nov 26Dec 1

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°F163156153149145141138133127
32°F183178173168164160156152144
28°F205199194189185181176171163
24°F225217212207203199195190183
20°F246236231226221217213208200
16°F263255249244239234228224216

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
6,696
Cooling degree days, base 65°F
831
Growing degree days, base 40°F
5,186
Growing degree days, base 45°F
4,070
Growing degree days, base 50°F
3,075
Growing degree days, base 55°F
2,200
Growing degree days, base 60°F
1,449

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,37800
February1,13501
March866126
April494498
May20047328
June24179605
July4282742
August11224677
September11787426
October4229153
November831020
December1,21401

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 16.4 km from Afton. 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 USC00131962 (Creston 2 Sw). Public domain.