Superior climate

Superior Frost Dates and Growing Season

NOAA 1991-2020 normals for Superior, 1.1 km from Superior, elevation 1512 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 April 29 and the first fall freeze around October 10, a growing season of about 162 days.

Median at 36°F
last May 7, first October 1
Median at 32°F
last April 29, first October 10
Median at 28°F
last April 19, first October 19

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 14May 11May 9May 7May 4May 2Apr 29Apr 26
32°FMay 10May 6May 3May 1Apr 29Apr 26Apr 23Apr 20Apr 15
28°FMay 2Apr 28Apr 25Apr 22Apr 19Apr 16Apr 13Apr 10Apr 5
24°FApr 25Apr 20Apr 17Apr 13Apr 10Apr 7Apr 4Mar 31Mar 26
20°FApr 16Apr 11Apr 7Apr 3Mar 31Mar 29Mar 24Mar 20Mar 12
16°FApr 8Apr 2Mar 30Mar 25Mar 21Mar 17Mar 13Mar 8Mar 2

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 17Sep 22Sep 26Sep 29Oct 1Oct 3Oct 6Oct 9Oct 14
32°FSep 26Sep 30Oct 3Oct 7Oct 10Oct 13Oct 15Oct 18Oct 22
28°FOct 3Oct 8Oct 13Oct 16Oct 19Oct 21Oct 25Oct 28Nov 1
24°FOct 14Oct 19Oct 23Oct 26Oct 29Oct 31Nov 3Nov 6Nov 10
20°FOct 23Oct 28Oct 31Nov 3Nov 5Nov 8Nov 11Nov 14Nov 20
16°FOct 30Nov 3Nov 7Nov 10Nov 13Nov 16Nov 19Nov 23Nov 28

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°F163157153149145142138134128
32°F181175171167162159154149144
28°F201194189185181178174168162
24°F218212208203200197192187180
20°F239231227223218214210205198
16°F259251245240236232228222213

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
6,052
Cooling degree days, base 65°F
1,104
Growing degree days, base 40°F
5,675
Growing degree days, base 45°F
4,509
Growing degree days, base 50°F
3,470
Growing degree days, base 55°F
2,556
Growing degree days, base 60°F
1,766

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,23400
February1,00003
March777133
April4457125
May16966374
June16237672
July2363826
August6292750
September87125491
October39114175
November782022
December1,14500

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 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 USC00258320 (Superior). Public domain.