Mitchell County climate

Mitchell County Frost Dates and Growing Season

NOAA 1991-2020 normals for Beloit, 11 km from Mitchell County, elevation 1391 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Beloit. 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 19, a growing season of about 181 days.

Median at 36°F
last April 29, first October 11
Median at 32°F
last April 19, first October 19
Median at 28°F
last April 8, first October 27

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 12May 7May 4May 1Apr 29Apr 25Apr 23Apr 20Apr 15
32°FMay 2Apr 28Apr 24Apr 21Apr 19Apr 15Apr 12Apr 9Apr 5
28°FApr 23Apr 19Apr 15Apr 12Apr 8Apr 5Apr 2Mar 30Mar 24
24°FApr 15Apr 9Apr 5Apr 2Mar 30Mar 27Mar 22Mar 18Mar 12
20°FApr 6Apr 1Mar 29Mar 25Mar 21Mar 17Mar 13Mar 9Mar 3
16°FMar 30Mar 22Mar 17Mar 13Mar 10Mar 6Mar 2Feb 27Feb 21

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 28Oct 1Oct 5Oct 9Oct 11Oct 14Oct 16Oct 19Oct 22
32°FOct 4Oct 11Oct 14Oct 16Oct 19Oct 21Oct 23Oct 26Oct 31
28°FOct 15Oct 19Oct 22Oct 25Oct 27Oct 30Nov 2Nov 6Nov 11
24°FOct 22Oct 28Oct 31Nov 3Nov 6Nov 9Nov 12Nov 17Nov 22
20°FOct 31Nov 5Nov 9Nov 12Nov 16Nov 20Nov 24Nov 27Dec 2
16°FNov 8Nov 14Nov 19Nov 24Nov 27Nov 30Dec 3Dec 7Dec 13

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°F181175170166162159155151145
32°F201195189185181177173168161
28°F223216211206202198194189183
24°F244235229224221217212207201
20°F264255249244239234229224216
16°F283275269265260255249242231

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
5,361
Cooling degree days, base 65°F
1,496
Growing degree days, base 40°F
6,425
Growing degree days, base 45°F
5,182
Growing degree days, base 50°F
4,070
Growing degree days, base 55°F
3,086
Growing degree days, base 60°F
2,227

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,14100
February91308
March690154
April36814173
May13096437
June9313754
July0468933
August2392856
September55184581
October31626234
November688140
December1,05101

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 11 km from Mitchell County. 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 USC00140693 (Beloit). Public domain.