Morrison climate

Morrison Frost Dates and Growing Season

NOAA 1991-2020 normals for Red Rock 7SSE Mesonet, 14.6 km from Morrison, elevation 961 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Red Rock 7SSE Mesonet. 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 8 and the first fall freeze around October 28, a growing season of about 202 days.

Median at 36°F
last April 19, first October 20
Median at 32°F
last April 8, first October 28
Median at 28°F
last March 28, first November 5

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 3Apr 29Apr 26Apr 22Apr 19Apr 16Apr 12Apr 9Apr 3
32°FApr 24Apr 18Apr 14Apr 11Apr 8Apr 4Apr 1Mar 29Mar 22
28°FApr 12Apr 8Apr 3Mar 31Mar 28Mar 23Mar 18Mar 13Mar 4
24°FApr 3Mar 28Mar 22Mar 18Mar 14Mar 10Mar 5Mar 1Feb 24
20°FMar 21Mar 14Mar 9Mar 5Mar 2Feb 28Feb 24Feb 19Feb 12
16°FMar 11Mar 4Mar 1Feb 25Feb 22Feb 17Feb 13Feb 5Jan 29

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°FOct 4Oct 10Oct 14Oct 17Oct 20Oct 22Oct 24Oct 28Nov 1
32°FOct 14Oct 20Oct 22Oct 25Oct 28Oct 31Nov 2Nov 6Nov 11
28°FOct 22Oct 27Oct 31Nov 2Nov 5Nov 9Nov 12Nov 17Nov 23
24°FOct 30Nov 3Nov 7Nov 12Nov 16Nov 20Nov 24Nov 29Dec 4
20°FNov 6Nov 13Nov 19Nov 23Nov 28Dec 2Dec 5Dec 10Dec 17
16°FNov 19Nov 26Dec 1Dec 5Dec 10Dec 15Dec 21Dec 28Jan 4

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°F203195191186182177173168161
32°F228218212207202198193187181
28°F249240233228224219214208200
24°F272264257252247241235229220
20°F297287280275270265259253244
16°F325315306299293287280273266

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
3,876
Cooling degree days, base 65°F
1,881
Growing degree days, base 40°F
7,636
Growing degree days, base 45°F
6,192
Growing degree days, base 50°F
4,901
Growing degree days, base 55°F
3,751
Growing degree days, base 60°F
2,745

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January880012
February685137
March47212137
April23337285
May64158561
June1361810
July0518982
August0488953
September25239665
October20461346
November501697
December810017

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 14.6 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 USC00347507 (Red Rock 7SSE Mesonet). Public domain.