Aurora climate

Aurora Frost Dates and Growing Season

NOAA 1991-2020 normals for Aurora, 2.3 km from Aurora, elevation 660 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Aurora. 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 19 and the first fall freeze around October 23, a growing season of about 185 days.

Median at 36°F
last May 1, first October 13
Median at 32°F
last April 19, first October 23
Median at 28°F
last April 8, first November 2

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 12May 7May 4May 1Apr 29Apr 25Apr 21Apr 17
32°FMay 4Apr 29Apr 25Apr 22Apr 19Apr 16Apr 13Apr 10Apr 5
28°FApr 23Apr 18Apr 15Apr 12Apr 8Apr 5Apr 3Mar 31Mar 25
24°FApr 13Apr 7Apr 3Apr 1Mar 30Mar 26Mar 22Mar 17Mar 11
20°FApr 1Mar 29Mar 24Mar 20Mar 17Mar 13Mar 10Mar 7Mar 1
16°FMar 24Mar 19Mar 14Mar 10Mar 7Mar 5Mar 2Feb 27Feb 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°FSep 29Oct 4Oct 8Oct 10Oct 13Oct 15Oct 18Oct 21Oct 25
32°FOct 9Oct 15Oct 18Oct 21Oct 23Oct 25Oct 28Oct 30Nov 3
28°FOct 21Oct 25Oct 29Oct 31Nov 2Nov 5Nov 8Nov 11Nov 16
24°FNov 1Nov 3Nov 7Nov 10Nov 12Nov 14Nov 17Nov 21Nov 26
20°FNov 8Nov 12Nov 15Nov 18Nov 21Nov 24Nov 27Dec 1Dec 6
16°FNov 15Nov 20Nov 24Nov 27Nov 30Dec 2Dec 6Dec 11Dec 18

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°F183177171167164160155150143
32°F205198194189185181177172164
28°F228221216211207203199193186
24°F250243238233229224220215209
20°F273264258253249245241235227
16°F292284278272267263258252246

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
6,256
Cooling degree days, base 65°F
911
Growing degree days, base 40°F
5,367
Growing degree days, base 45°F
4,220
Growing degree days, base 50°F
3,204
Growing degree days, base 55°F
2,309
Growing degree days, base 60°F
1,542

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,29400
February1,05802
March840227
April4707108
May19558340
June30189609
July3294756
August6242701
September90106469
October38613166
November758024
December1,12502

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 2.3 km from Aurora. 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 USC00110338 (Aurora). Public domain.