Ypsilanti climate

Ypsilanti Frost Dates and Growing Season

NOAA 1991-2020 normals for Ann Arbor Se, 6.6 km from Ypsilanti, elevation 832 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Ann Arbor Se. 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 10, a growing season of about 157 days.

Median at 36°F
last May 15, first October 1
Median at 32°F
last May 5, first October 10
Median at 28°F
last April 24, first October 23

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 29May 25May 22May 18May 15May 12May 9May 5May 1
32°FMay 20May 15May 11May 8May 5May 2Apr 30Apr 26Apr 21
28°FMay 11May 5May 1Apr 28Apr 24Apr 21Apr 19Apr 16Apr 10
24°FApr 27Apr 21Apr 17Apr 15Apr 11Apr 9Apr 6Apr 3Mar 31
20°FApr 15Apr 10Apr 6Apr 3Apr 1Mar 29Mar 24Mar 20Mar 15
16°FApr 3Mar 30Mar 27Mar 23Mar 20Mar 17Mar 14Mar 10Mar 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°FSep 18Sep 22Sep 25Sep 28Oct 1Oct 3Oct 5Oct 8Oct 12
32°FSep 28Oct 1Oct 4Oct 7Oct 10Oct 13Oct 16Oct 20Oct 24
28°FOct 7Oct 13Oct 18Oct 21Oct 23Oct 26Oct 30Nov 1Nov 6
24°FOct 22Oct 27Oct 31Nov 2Nov 5Nov 8Nov 10Nov 14Nov 18
20°FNov 2Nov 6Nov 10Nov 13Nov 16Nov 19Nov 23Nov 28Dec 3
16°FNov 10Nov 17Nov 22Nov 25Nov 29Dec 2Dec 6Dec 10Dec 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°F157150145141137133129124117
32°F176170165161157154150145138
28°F199192188184180176172167160
24°F226219214210207202198192186
20°F253245239234230226221216211
16°F279270264259253249243237229

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
6,680
Cooling degree days, base 65°F
594
Growing degree days, base 40°F
4,703
Growing degree days, base 45°F
3,613
Growing degree days, base 50°F
2,659
Growing degree days, base 55°F
1,836
Growing degree days, base 60°F
1,141

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,27101
February1,10401
March931114
April565161
May24930270
June47125528
July10211666
August18164611
September13456377
October4556115
November786015
December1,11001

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 6.6 km from Ypsilanti. 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 USC00200228 (Ann Arbor Se). Public domain.