Mount Morris climate

Mount Morris Frost Dates and Growing Season

NOAA 1991-2020 normals for Mt Morris 2 W, 2.6 km from Mount Morris, elevation 880 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Mt Morris 2 W. 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 30 and the first fall freeze around October 17, a growing season of about 170 days.

Median at 36°F
last May 9, first October 4
Median at 32°F
last April 30, first October 17
Median at 28°F
last April 18, first November 1

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 25May 20May 15May 12May 9May 6May 3Apr 30Apr 26
32°FMay 13May 9May 5May 2Apr 30Apr 27Apr 24Apr 21Apr 17
28°FMay 2Apr 29Apr 25Apr 21Apr 18Apr 16Apr 12Apr 8Apr 4
24°FApr 19Apr 16Apr 12Apr 8Apr 6Apr 3Apr 2Mar 30Mar 23
20°FApr 10Apr 5Apr 3Mar 31Mar 30Mar 27Mar 23Mar 19Mar 14
16°FApr 1Mar 30Mar 27Mar 23Mar 20Mar 18Mar 14Mar 11Mar 3

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 22Sep 27Sep 30Oct 2Oct 4Oct 7Oct 10Oct 14Oct 19
32°FOct 1Oct 6Oct 10Oct 13Oct 17Oct 20Oct 24Oct 28Nov 2
28°FOct 13Oct 20Oct 25Oct 29Nov 1Nov 3Nov 6Nov 11Nov 15
24°FOct 31Nov 4Nov 7Nov 11Nov 13Nov 16Nov 19Nov 23Dec 1
20°FNov 10Nov 14Nov 18Nov 21Nov 24Nov 27Dec 1Dec 4Dec 10
16°FNov 19Nov 24Nov 28Dec 1Dec 4Dec 8Dec 12Dec 17Dec 23

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°F166160155150147143139134127
32°F190184179174170166161156148
28°F216209203199195190185180172
24°F241234229225220216213207201
20°F263256249245241237233228220
16°F282275270265261257251246239

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
6,778
Cooling degree days, base 65°F
522
Growing degree days, base 40°F
4,587
Growing degree days, base 45°F
3,500
Growing degree days, base 50°F
2,547
Growing degree days, base 55°F
1,730
Growing degree days, base 60°F
1,047

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,28901
February1,10701
March988011
April596364
May26438268
June69100482
July15181631
August24142583
September14251365
October4506117
November747023
December1,08702

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 2.6 km from Mount Morris. 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 USC00305597 (Mt Morris 2 W). Public domain.