Saint Clair climate

Saint Clair Frost Dates and Growing Season

NOAA 1991-2020 normals for Mankato, 15.3 km from Saint Clair, elevation 850 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Mankato. 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 30 and the first fall freeze around October 9, a growing season of about 161 days.

Median at 36°F
last May 8, first September 30
Median at 32°F
last April 30, first October 9
Median at 28°F
last April 19, first October 20

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 23May 17May 14May 11May 8May 6May 3May 1Apr 26
32°FMay 12May 7May 4May 2Apr 30Apr 27Apr 24Apr 20Apr 16
28°FMay 2Apr 28Apr 25Apr 22Apr 19Apr 17Apr 14Apr 10Apr 6
24°FApr 23Apr 19Apr 15Apr 12Apr 10Apr 7Apr 4Apr 2Mar 28
20°FApr 17Apr 10Apr 7Apr 4Apr 2Mar 31Mar 28Mar 22Mar 16
16°FApr 9Apr 4Mar 31Mar 28Mar 24Mar 21Mar 17Mar 14Mar 10

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 21Sep 25Sep 27Sep 30Oct 1Oct 4Oct 7Oct 12
32°FSep 25Sep 29Oct 2Oct 5Oct 9Oct 12Oct 14Oct 18Oct 22
28°FOct 4Oct 10Oct 14Oct 18Oct 20Oct 22Oct 25Oct 27Nov 1
24°FOct 17Oct 22Oct 24Oct 27Oct 29Nov 1Nov 3Nov 6Nov 11
20°FOct 26Oct 31Nov 1Nov 4Nov 6Nov 9Nov 12Nov 17Nov 23
16°FNov 2Nov 5Nov 9Nov 11Nov 15Nov 18Nov 21Nov 25Dec 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°F160154150146143139135131124
32°F179172168165161158153149141
28°F201196190186182178175170163
24°F220214209205201197193189182
20°F239231226221217214210206199
16°F258250244239235230226220214

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
7,789
Cooling degree days, base 65°F
632
Growing degree days, base 40°F
4,594
Growing degree days, base 45°F
3,569
Growing degree days, base 50°F
2,657
Growing degree days, base 55°F
1,859
Growing degree days, base 60°F
1,176

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,55900
February1,28800
March1,04207
April596262
May25137279
June45143548
July9220676
August23161603
September15662366
October5168106
November929012
December1,37500

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 15.3 km from Saint Clair. 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 USC00215073 (Mankato). Public domain.