Saint Clair climate

Saint Clair Frost Dates and Growing Season

NOAA 1991-2020 normals for Port Huron, 18 km from Saint Clair, elevation 590 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Port Huron. 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 November 3, a growing season of about 196 days.

Median at 36°F
last May 1, first October 22
Median at 32°F
last April 19, first November 3
Median at 28°F
last April 7, first November 12

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

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°F192184180175172168163158151
32°F215208204200196193188184176
28°F239232227222219214211205199
24°F261254248244239235231226220
20°F283274268263259255249244237
16°F301295289284278273268263255

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
6,343
Cooling degree days, base 65°F
749
Growing degree days, base 40°F
4,999
Growing degree days, base 45°F
3,880
Growing degree days, base 50°F
2,898
Growing degree days, base 55°F
2,049
Growing degree days, base 60°F
1,330

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,22700
February1,06700
March922011
April569262
May26035265
June56134529
July5261721
August8220677
September8988450
October37410161
November719022
December1,04801

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 18 km from Saint Clair. 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 USC00206680 (Port Huron). Public domain.