Ortonville climate

Ortonville Frost Dates and Growing Season

NOAA 1991-2020 normals for Milbank, 16.4 km from Ortonville, elevation 1142 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Milbank. 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 2, a growing season of about 150 days.

Median at 36°F
last May 14, first September 24
Median at 32°F
last May 5, first October 2
Median at 28°F
last April 25, first October 13

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 27May 23May 19May 17May 14May 12May 10May 7May 3
32°FMay 18May 14May 11May 8May 5May 3May 1Apr 28Apr 22
28°FMay 9May 4May 1Apr 29Apr 25Apr 22Apr 19Apr 16Apr 10
24°FApr 30Apr 25Apr 21Apr 18Apr 15Apr 11Apr 8Apr 6Apr 2
20°FApr 21Apr 16Apr 11Apr 8Apr 6Apr 4Apr 2Mar 30Mar 23
16°FApr 13Apr 8Apr 4Apr 2Mar 31Mar 29Mar 25Mar 21Mar 14

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 12Sep 16Sep 19Sep 22Sep 24Sep 26Sep 29Oct 1Oct 5
32°FSep 20Sep 25Sep 28Sep 30Oct 2Oct 5Oct 8Oct 10Oct 15
28°FSep 29Oct 3Oct 6Oct 9Oct 13Oct 16Oct 19Oct 22Oct 26
24°FOct 8Oct 13Oct 18Oct 21Oct 24Oct 27Oct 30Nov 2Nov 8
20°FOct 19Oct 24Oct 28Oct 31Nov 2Nov 5Nov 8Nov 11Nov 16
16°FOct 28Nov 1Nov 5Nov 8Nov 10Nov 13Nov 16Nov 19Nov 25

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°F148143139135132129126121116
32°F167161157153150146142138132
28°F187181176172168164160155149
24°F210204199194190186182176169
20°F228222217212208204200194187
16°F246239234228224220214209203

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
8,452
Cooling degree days, base 65°F
483
Growing degree days, base 40°F
4,223
Growing degree days, base 45°F
3,244
Growing degree days, base 50°F
2,372
Growing degree days, base 55°F
1,620
Growing degree days, base 60°F
981

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,63600
February1,36700
March1,13507
April667144
May31023228
June55101497
July12186638
August30129564
September19239311
October584480
November1,01005
December1,45400

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 16.4 km from Ortonville. 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 USC00395531 (Milbank). Public domain.