St. Clair County climate

St. Clair County Frost Dates and Growing Season

NOAA 1991-2020 normals for Osceola, 6.5 km from St. Clair County, elevation 744 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Osceola. 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 16 and the first fall freeze around October 24, a growing season of about 189 days.

Median at 36°F
last April 27, first October 13
Median at 32°F
last April 16, first October 24
Median at 28°F
last April 4, first November 1

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 11May 6May 2Apr 30Apr 27Apr 23Apr 20Apr 16Apr 11
32°FMay 3Apr 27Apr 23Apr 19Apr 16Apr 13Apr 9Apr 5Mar 31
28°FApr 21Apr 16Apr 11Apr 8Apr 4Apr 1Mar 30Mar 25Mar 18
24°FApr 11Apr 5Apr 1Mar 29Mar 25Mar 21Mar 17Mar 12Mar 6
20°FApr 2Mar 27Mar 22Mar 17Mar 13Mar 9Mar 5Mar 1Feb 25
16°FMar 20Mar 14Mar 9Mar 6Mar 3Feb 28Feb 25Feb 20Feb 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 29Oct 4Oct 8Oct 10Oct 13Oct 16Oct 19Oct 22Oct 25
32°FOct 10Oct 14Oct 18Oct 21Oct 24Oct 25Oct 28Oct 31Nov 3
28°FOct 19Oct 25Oct 28Oct 30Nov 1Nov 3Nov 5Nov 8Nov 15
24°FOct 27Nov 1Nov 3Nov 6Nov 8Nov 12Nov 15Nov 19Nov 26
20°FNov 3Nov 7Nov 12Nov 14Nov 18Nov 22Nov 27Dec 1Dec 6
16°FNov 10Nov 17Nov 22Nov 26Nov 30Dec 3Dec 7Dec 13Dec 19

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°F189182177173169165162156149
32°F210203197193189185181175169
28°F233224218214209205201196187
24°F255246239234229225220215207
20°F276267261256251245240234226
16°F298289282277272267261255246

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
4,640
Cooling degree days, base 65°F
1,490
Growing degree days, base 40°F
6,809
Growing degree days, base 45°F
5,476
Growing degree days, base 50°F
4,274
Growing degree days, base 55°F
3,208
Growing degree days, base 60°F
2,277

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,03206
February814017
March583691
April29624227
May92115491
June5297742
July0440905
August1396860
September47173577
October25934276
November593371
December919012

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 6.5 km from St. Clair 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 USC00236402 (Osceola). Public domain.