Evanston climate

Evanston Frost Dates and Growing Season

NOAA 1991-2020 normals for Evanston 1 E, 1.1 km from Evanston, elevation 6825 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Evanston 1 E. 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 12 and the first fall freeze around September 12, a growing season of about 90 days.

Median at 32°F
last June 12, first September 12
Median at 28°F
last May 24, first September 24

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 2Jun 24Jun 20Jun 16Jun 12Jun 9Jun 6Jun 1May 26
28°FJun 14Jun 7Jun 2May 29May 24May 19May 16May 11May 5
24°FMay 26May 18May 13May 9May 5May 2Apr 30Apr 26Apr 21
20°FMay 7May 1Apr 27Apr 23Apr 20Apr 17Apr 13Apr 10Apr 5
16°FApr 23Apr 17Apr 13Apr 9Apr 5Apr 2Mar 30Mar 23Mar 16

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 26Sep 2Sep 6Sep 9Sep 12Sep 15Sep 18Sep 21Sep 25
28°FSep 7Sep 14Sep 19Sep 22Sep 24Sep 27Oct 1Oct 3Oct 9
24°FSep 21Sep 27Oct 1Oct 3Oct 6Oct 10Oct 14Oct 18Oct 23
20°FOct 1Oct 6Oct 12Oct 16Oct 20Oct 23Oct 26Oct 30Nov 4
16°FOct 16Oct 21Oct 25Oct 27Oct 31Nov 2Nov 5Nov 8Nov 14

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°F857873696359534637
32°F11310599949085807362
28°F14413613012612111511010493
24°F175168162156151146142135127
20°F203195190185181176170164155
16°F229222216212207202198191183

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
8,457
Cooling degree days, base 65°F
84
Growing degree days, base 40°F
3,030
Growing degree days, base 45°F
2,112
Growing degree days, base 50°F
1,359
Growing degree days, base 55°F
760
Growing degree days, base 60°F
327

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,33800
February1,14900
March1,00400
April74608
May501071
June2435228
July6849446
August8528409
September3122172
October660025
November1,01401
December1,33600

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 1.1 km from Evanston. 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 USC00483100 (Evanston 1 E). Public domain.