Aurora climate

Aurora Frost Dates and Growing Season

NOAA 1991-2020 normals for Aurora State AP, 2.2 km from Aurora, elevation 196 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Aurora State AP. 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 March 16 and the first fall freeze around November 14, a growing season of about 242 days.

Median at 36°F
last April 15, first October 26
Median at 32°F
last March 16, first November 14
Median at 28°F
last February 15, first December 1

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 29Apr 24Apr 19Apr 15Apr 11Apr 6Apr 2Mar 27
32°FApr 7Mar 31Mar 25Mar 20Mar 16Mar 11Mar 6Feb 28Feb 21
28°FMar 8Feb 28Feb 24Feb 19Feb 15Feb 8Jan 31Jan 19Jan 4
24°FFeb 18Feb 9Feb 1Jan 22Jan 12Jan 3Dec 27Dec 15Dec 6
20°FFeb 7Jan 23Jan 6Dec 30Dec 25Dec 17Dec 13Dec 7Dec 2
16°F–––––––––

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 9Oct 15Oct 19Oct 23Oct 26Oct 30Nov 2Nov 7Nov 14
32°FOct 27Nov 1Nov 5Nov 10Nov 14Nov 18Nov 23Nov 29Dec 6
28°FNov 9Nov 16Nov 22Nov 27Dec 1Dec 6Dec 12Dec 20Dec 30
24°FNov 21Nov 29Dec 5Dec 10Dec 17Dec 24Dec 30Jan 7Jan 26
20°FNov 27Dec 2Dec 7Dec 11Dec 17Dec 24Dec 28Jan 6Jan 29
16°F–––––––––

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°F219211204199193189183177167
32°F276262255248242236230223215
28°F332317308300292284276266255
24°F365365358349340333324315304
20°F365365365365365365364346333
16°F365365365365365365365365365

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
99% of years
24°F or colder
76% of years
20°F or colder
31% of years
16°F or colder
7% 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
4,162
Cooling degree days, base 65°F
455
Growing degree days, base 40°F
5,543
Growing degree days, base 45°F
3,983
Growing degree days, base 50°F
2,707
Growing degree days, base 55°F
1,726
Growing degree days, base 60°F
978

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January70107
February56709
March519038
April3832102
May21420274
June9648402
July13156608
August12161614
September7165444
October3174171
November549030
December72108

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 2.2 km from Aurora. 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 USW00094281 (Aurora State AP). Public domain.