St. Charles climate

St. Charles Frost Dates and Growing Season

NOAA 1991-2020 normals for Mechanicsville 5 Ne, 21.5 km from St. Charles, elevation 100 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Mechanicsville 5 Ne. 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 17 and the first fall freeze around October 27, a growing season of about 195 days.

Median at 36°F
last April 30, first October 16
Median at 32°F
last April 17, first October 27
Median at 28°F
last April 2, first November 6

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

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 3Oct 7Oct 10Oct 13Oct 16Oct 19Oct 23Oct 26Oct 31
32°FOct 12Oct 17Oct 20Oct 24Oct 27Oct 31Nov 1Nov 4Nov 9
28°FOct 24Oct 28Nov 1Nov 3Nov 6Nov 9Nov 13Nov 17Nov 23
24°FNov 3Nov 8Nov 12Nov 16Nov 20Nov 24Nov 29Dec 2Dec 8
20°FNov 14Nov 22Nov 27Dec 1Dec 3Dec 7Dec 13Dec 21Dec 29
16°FNov 30Dec 4Dec 9Dec 15Dec 20Dec 26Dec 30Jan 5Jan 14

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°F192184178174170165161156149
32°F215209203199195191186181173
28°F242234228223219215210206198
24°F269260254249244240235228219
20°F298289282276271267261255245
16°F327316309304299293287280272

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
99% 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
4,589
Cooling degree days, base 65°F
1,029
Growing degree days, base 40°F
6,181
Growing degree days, base 45°F
4,837
Growing degree days, base 50°F
3,649
Growing degree days, base 55°F
2,619
Growing degree days, base 60°F
1,746

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January945010
February787011
March645255
April32421195
May13366400
June17203636
July0329793
August2273736
September53119516
October29715213
November559164
December826018

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 21.5 km from St. Charles. 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 USC00185865 (Mechanicsville 5 Ne). Public domain.