Morrison climate

Morrison Frost Dates and Growing Season

NOAA 1991-2020 normals for Morrison, 1.8 km from Morrison, elevation 632 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Morrison. 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 26 and the first fall freeze around October 13, a growing season of about 167 days.

Median at 36°F
last May 6, first October 3
Median at 32°F
last April 26, first October 13
Median at 28°F
last April 15, 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 22May 17May 13May 9May 6May 3Apr 30Apr 27Apr 23
32°FMay 11May 6May 2Apr 29Apr 26Apr 23Apr 20Apr 17Apr 13
28°FApr 30Apr 24Apr 20Apr 17Apr 15Apr 11Apr 8Apr 5Apr 2
24°FApr 18Apr 13Apr 9Apr 5Apr 3Apr 1Mar 30Mar 23Mar 16
20°FApr 8Apr 2Mar 31Mar 28Mar 23Mar 20Mar 16Mar 12Mar 7
16°FMar 29Mar 23Mar 19Mar 16Mar 13Mar 10Mar 7Mar 4Feb 28

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 25Sep 28Oct 1Oct 3Oct 6Oct 8Oct 11Oct 15
32°FSep 30Oct 5Oct 9Oct 11Oct 13Oct 15Oct 18Oct 21Oct 25
28°FOct 11Oct 15Oct 19Oct 21Oct 23Oct 25Oct 28Oct 30Nov 3
24°FOct 21Oct 25Oct 28Oct 31Nov 1Nov 4Nov 7Nov 11Nov 16
20°FNov 1Nov 3Nov 7Nov 10Nov 13Nov 16Nov 19Nov 23Nov 28
16°FNov 8Nov 13Nov 17Nov 20Nov 23Nov 25Nov 28Dec 1Dec 7

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°F166160156152149145141137130
32°F188180175171167164160155150
28°F208201197193189185181176169
24°F233227221216212208204199192
20°F256249243238233230226221213
16°F276267261257253248244238232

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
6,747
Cooling degree days, base 65°F
705
Growing degree days, base 40°F
4,951
Growing degree days, base 45°F
3,853
Growing degree days, base 50°F
2,876
Growing degree days, base 55°F
2,022
Growing degree days, base 60°F
1,295

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,38100
February1,13001
March885019
April507386
May20645319
June32160578
July6240699
August14181632
September12568398
October4477127
November816016
December1,19702

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 1.8 km from Morrison. 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 USC00115833 (Morrison). Public domain.