South Lyon climate

South Lyon Frost Dates and Growing Season

NOAA 1991-2020 normals for Whitmore Lake 1NW, 11.1 km from South Lyon, elevation 906 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Whitmore Lake 1NW. 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 May 5 and the first fall freeze around October 13, a growing season of about 160 days.

Median at 36°F
last May 17, first October 1
Median at 32°F
last May 5, first October 13
Median at 28°F
last April 26, first October 26

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

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 20Sep 24Sep 27Sep 30Oct 1Oct 4Oct 6Oct 10Oct 13
32°FSep 30Oct 3Oct 7Oct 10Oct 13Oct 16Oct 19Oct 22Oct 26
28°FOct 12Oct 18Oct 22Oct 24Oct 26Oct 29Nov 1Nov 3Nov 7
24°FOct 28Nov 1Nov 3Nov 5Nov 7Nov 9Nov 12Nov 15Nov 20
20°FNov 5Nov 9Nov 12Nov 15Nov 18Nov 21Nov 25Nov 28Dec 3
16°FNov 13Nov 18Nov 22Nov 26Nov 28Dec 1Dec 5Dec 11Dec 17

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°F157151146142139135131126119
32°F180174169164160156152148140
28°F202197192188184180176171164
24°F228220215212208205200195187
20°F252245239234230226222218212
16°F274266261256251246242236229

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
6,967
Cooling degree days, base 65°F
480
Growing degree days, base 40°F
4,466
Growing degree days, base 45°F
3,397
Growing degree days, base 50°F
2,470
Growing degree days, base 55°F
1,667
Growing degree days, base 60°F
993

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,32000
February1,15300
March968114
April592155
May27622243
June6688474
July17177625
August25135575
September14652360
October4685110
November801014
December1,13301

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 11.1 km from South Lyon. 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 USC00208972 (Whitmore Lake 1NW). Public domain.