Afton climate

Afton Frost Dates and Growing Season

NOAA 1991-2020 normals for Afton, 1.2 km from Afton, elevation 6248 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Afton. 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 June 20 and the first fall freeze around September 1, a growing season of about 71 days.

Median at 32°F
last June 20, first September 1
Median at 28°F
last June 1, first September 13

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°F–––––––––
32°FJul 7Jul 1Jun 27Jun 24Jun 20Jun 17Jun 14Jun 10Jun 2
28°FJun 20Jun 14Jun 9Jun 5Jun 1May 28May 22May 16May 10
24°FMay 30May 22May 16May 12May 9May 5May 2Apr 29Apr 24
20°FMay 10May 4Apr 30Apr 27Apr 24Apr 20Apr 17Apr 13Apr 8
16°FApr 26Apr 19Apr 15Apr 12Apr 8Apr 6Apr 3Mar 31Mar 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°F–––––––––
32°FAug 12Aug 20Aug 27Aug 30Sep 1Sep 4Sep 8Sep 11Sep 15
28°FAug 29Sep 3Sep 7Sep 10Sep 13Sep 16Sep 19Sep 22Sep 27
24°FSep 12Sep 17Sep 20Sep 23Sep 27Sep 29Oct 2Oct 6Oct 12
20°FSep 24Sep 29Oct 2Oct 6Oct 10Oct 14Oct 17Oct 21Oct 25
16°FOct 7Oct 13Oct 17Oct 20Oct 23Oct 26Oct 29Nov 1Nov 6

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°F655650464238343024
32°F938680757166615549
28°F12812011310810499938777
24°F160153147142137132127120112
20°F187180176172168163159153145
16°F216208203199194190185180172

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
9,688
Cooling degree days, base 65°F
41
Growing degree days, base 40°F
2,537
Growing degree days, base 45°F
1,724
Growing degree days, base 50°F
1,061
Growing degree days, base 55°F
551
Growing degree days, base 60°F
206

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,54200
February1,28700
March1,13500
April82503
May566043
June3161169
July11524376
August14116343
September3950117
October755011
November1,11600
December1,49600

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 1.2 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 USC00480027 (Afton). Public domain.