Superior climate

Superior Frost Dates and Growing Season

NOAA 1991-2020 normals for Superior, 2.5 km from Superior, elevation 607 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Superior. 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 May 6 and the first fall freeze around October 9, a growing season of about 154 days.

Median at 36°F
last May 21, first September 28
Median at 32°F
last May 6, first October 9
Median at 28°F
last April 24, first October 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°FJun 8Jun 3May 30May 25May 21May 17May 15May 11May 6
32°FMay 25May 19May 15May 10May 6May 4May 1Apr 29Apr 24
28°FMay 9May 2Apr 29Apr 26Apr 24Apr 21Apr 19Apr 16Apr 10
24°FApr 26Apr 21Apr 19Apr 16Apr 13Apr 11Apr 8Apr 5Apr 1
20°FApr 19Apr 15Apr 12Apr 9Apr 6Apr 4Apr 1Mar 29Mar 22
16°FApr 12Apr 7Apr 4Apr 1Mar 29Mar 26Mar 22Mar 17Mar 13

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 15Sep 20Sep 23Sep 25Sep 28Oct 1Oct 3Oct 6Oct 11
32°FSep 24Sep 29Oct 2Oct 6Oct 9Oct 12Oct 16Oct 20Oct 24
28°FOct 6Oct 12Oct 16Oct 21Oct 24Oct 27Oct 30Nov 2Nov 7
24°FOct 19Oct 25Oct 30Nov 1Nov 3Nov 6Nov 9Nov 12Nov 17
20°FOct 30Nov 2Nov 6Nov 9Nov 11Nov 14Nov 17Nov 20Nov 25
16°FNov 4Nov 8Nov 11Nov 15Nov 18Nov 20Nov 23Nov 27Dec 1

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°F150143138133130126120114108
32°F175169163159154151145141132
28°F201195190186181177172167159
24°F220213209205201197194188182
20°F237230225222217214210206200
16°F253245240235232228224219213

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
8,822
Cooling degree days, base 65°F
267
Growing degree days, base 40°F
3,376
Growing degree days, base 45°F
2,468
Growing degree days, base 50°F
1,706
Growing degree days, base 55°F
1,084
Growing degree days, base 60°F
600

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,57600
February1,31600
March1,13000
April783010
May494382
June22926260
July58121529
August5295508
September22121263
October596150
November98003
December1,38900

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 2.5 km from Superior. 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 USC00478349 (Superior). Public domain.