Colby climate

Colby Frost Dates and Growing Season

NOAA 1991-2020 normals for Owen 1E, 19 km from Colby, elevation 1238 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Owen 1E. 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 13 and the first fall freeze around September 26, a growing season of about 136 days.

Median at 36°F
last May 25, first September 17
Median at 32°F
last May 13, first September 26
Median at 28°F
last May 2, first October 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°FJun 9Jun 3May 31May 28May 25May 22May 19May 15May 11
32°FMay 29May 23May 19May 16May 13May 10May 7May 3Apr 29
28°FMay 17May 12May 8May 5May 2Apr 30Apr 27Apr 23Apr 18
24°FMay 6May 1Apr 28Apr 24Apr 21Apr 17Apr 14Apr 11Apr 6
20°FApr 25Apr 19Apr 16Apr 13Apr 10Apr 7Apr 4Apr 1Mar 28
16°FApr 17Apr 12Apr 8Apr 5Apr 3Apr 1Mar 29Mar 25Mar 20

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 2Sep 8Sep 11Sep 14Sep 17Sep 20Sep 23Sep 26Oct 1
32°FSep 12Sep 17Sep 21Sep 24Sep 26Sep 29Oct 1Oct 5Oct 10
28°FSep 22Sep 27Sep 30Oct 3Oct 5Oct 9Oct 12Oct 15Oct 21
24°FOct 1Oct 6Oct 10Oct 14Oct 18Oct 21Oct 25Oct 29Nov 2
20°FOct 12Oct 19Oct 25Oct 28Nov 1Nov 2Nov 5Nov 9Nov 16
16°FOct 29Nov 1Nov 4Nov 7Nov 11Nov 14Nov 17Nov 21Nov 26

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°F13512912311911511110710192
32°F155148143140136132126122116
28°F175169164160156152148143135
24°F202195188183178174169163156
20°F223216212207204199195189182
16°F243235230226222217213208201

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
8,789
Cooling degree days, base 65°F
324
Growing degree days, base 40°F
3,776
Growing degree days, base 45°F
2,835
Growing degree days, base 50°F
2,010
Growing degree days, base 55°F
1,305
Growing degree days, base 60°F
736

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,66000
February1,39900
March1,15807
April703134
May34317194
June9970424
July39121547
August6384487
September24729260
October630255
November1,01104
December1,44000

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 19 km from Colby. 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 USC00476357 (Owen 1E). Public domain.