Saint Charles climate

Saint Charles Frost Dates and Growing Season

NOAA 1991-2020 normals for St Charles Elm Pt, 4.4 km from Saint Charles, elevation 472 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for St Charles Elm Pt. 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 8 and the first fall freeze around October 29, a growing season of about 203 days.

Median at 36°F
last April 21, first October 19
Median at 32°F
last April 8, first October 29
Median at 28°F
last March 30, first November 10

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 5Apr 30Apr 26Apr 23Apr 21Apr 18Apr 14Apr 10Apr 5
32°FApr 24Apr 20Apr 16Apr 11Apr 8Apr 5Apr 3Mar 31Mar 23
28°FApr 15Apr 8Apr 4Apr 1Mar 30Mar 26Mar 20Mar 15Mar 9
24°FApr 3Mar 30Mar 25Mar 20Mar 16Mar 12Mar 9Mar 5Feb 28
20°FMar 22Mar 16Mar 12Mar 9Mar 6Mar 3Feb 28Feb 23Feb 16
16°FMar 16Mar 10Mar 5Mar 2Feb 28Feb 23Feb 18Feb 11Feb 4

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°FOct 7Oct 11Oct 14Oct 17Oct 19Oct 22Oct 24Oct 27Oct 31
32°FOct 16Oct 21Oct 24Oct 27Oct 29Nov 1Nov 3Nov 6Nov 12
28°FOct 29Nov 1Nov 4Nov 6Nov 10Nov 12Nov 16Nov 22Nov 28
24°FNov 6Nov 10Nov 13Nov 17Nov 21Nov 25Nov 29Dec 3Dec 8
20°FNov 12Nov 18Nov 23Nov 27Dec 1Dec 4Dec 8Dec 13Dec 20
16°FNov 24Nov 30Dec 4Dec 8Dec 12Dec 18Dec 22Dec 27Jan 2

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°F200193188184180176172168161
32°F225216211206203199195189183
28°F249241235230225220216210204
24°F273264257253248243239234227
20°F293285278273269264258253245
16°F315305298294289283278272262

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
4,805
Cooling degree days, base 65°F
1,387
Growing degree days, base 40°F
6,597
Growing degree days, base 45°F
5,281
Growing degree days, base 50°F
4,108
Growing degree days, base 55°F
3,069
Growing degree days, base 60°F
2,159

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,06305
February842013
March641468
April31325218
May96113484
June9285726
July0408873
August2352815
September49163565
October27535261
November594369
December922012

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 4.4 km from Saint Charles. 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 USC00237397 (St Charles Elm Pt). Public domain.