Aurora Frost Dates and Growing Season

NOAA 1991-2020 normals for Embarrass, 12.6 km from Aurora, elevation 1425 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Embarrass. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

NOAA does not state freeze dates for this station.

Median at 28°F: last May 28, first September 18

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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	–	–	–	–	–	–	–	–	–
32°F	–	–	–	–	–	–	–	–	–
28°F	Jun 15	Jun 7	Jun 2	May 31	May 28	May 25	May 22	May 18	May 12
24°F	May 31	May 27	May 23	May 19	May 15	May 11	May 8	May 4	Apr 30
20°F	May 19	May 14	May 10	May 6	May 4	May 1	Apr 29	Apr 26	Apr 20
16°F	May 9	May 4	May 1	Apr 29	Apr 26	Apr 22	Apr 19	Apr 16	Apr 11

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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	–	–	–	–	–	–	–	–	–
32°F	–	–	–	–	–	–	–	–	–
28°F	Sep 1	Sep 5	Sep 10	Sep 13	Sep 18	Sep 22	Sep 26	Oct 1	Oct 4
24°F	Sep 11	Sep 17	Sep 22	Sep 26	Sep 30	Oct 2	Oct 6	Oct 9	Oct 13
20°F	Sep 23	Sep 29	Oct 3	Oct 6	Oct 10	Oct 14	Oct 18	Oct 22	Oct 29
16°F	Oct 5	Oct 13	Oct 18	Oct 22	Oct 25	Oct 29	Nov 1	Nov 4	Nov 9

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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	81	71	64	58	52	46	41	35	28
32°F	109	99	94	87	83	77	69	61	50
28°F	136	129	122	116	111	105	99	94	87
24°F	158	150	145	140	136	132	127	120	112
20°F	179	172	167	163	158	154	149	143	136
16°F	202	195	189	185	181	177	171	165	157

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: 10,529
Cooling degree days, base 65°F: 136
Growing degree days, base 40°F: 2,874
Growing degree days, base 45°F: 2,046
Growing degree days, base 50°F: 1,347
Growing degree days, base 55°F: 783
Growing degree days, base 60°F: 377

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	1,868	0	0
February	1,572	0	0
March	1,325	0	2
April	863	0	10
May	498	5	92
June	206	26	281
July	105	57	417
August	151	38	355
September	357	10	164
October	770	0	24
November	1,176	0	1
December	1,638	0	0

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 12.6 km from Aurora. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00212576 (Embarrass). Public domain.