Thomas County climate

Thomas County Frost Dates and Growing Season

NOAA 1991-2020 normals for Colby 1SW, 4.8 km from Thomas County, elevation 3170 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Colby 1SW. 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 2 and the first fall freeze around October 9, a growing season of about 156 days.

Median at 36°F
last May 13, first September 30
Median at 32°F
last May 2, first October 9
Median at 28°F
last April 23, first October 18

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 26May 21May 18May 15May 13May 11May 8May 5May 1
32°FMay 15May 11May 8May 5May 2Apr 30Apr 28Apr 25Apr 20
28°FMay 7May 2Apr 29Apr 26Apr 23Apr 21Apr 18Apr 15Apr 11
24°FApr 27Apr 22Apr 19Apr 16Apr 13Apr 10Apr 7Apr 4Mar 30
20°FApr 19Apr 13Apr 9Apr 6Apr 3Mar 31Mar 27Mar 22Mar 15
16°FApr 10Apr 4Apr 1Mar 28Mar 24Mar 19Mar 14Mar 9Mar 5

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 17Sep 22Sep 25Sep 28Sep 30Oct 2Oct 5Oct 8Oct 12
32°FSep 26Sep 30Oct 3Oct 6Oct 9Oct 12Oct 14Oct 17Oct 21
28°FOct 4Oct 9Oct 13Oct 16Oct 18Oct 20Oct 22Oct 25Oct 29
24°FOct 14Oct 18Oct 22Oct 24Oct 27Oct 29Nov 1Nov 4Nov 8
20°FOct 20Oct 26Oct 29Nov 1Nov 3Nov 6Nov 9Nov 12Nov 18
16°FOct 29Nov 2Nov 5Nov 9Nov 12Nov 15Nov 19Nov 23Nov 28

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°F155150146142139135131126119
32°F174168164160156153150144139
28°F195188184180176172168164156
24°F215209204199196191187182174
20°F236228222218214209205199191
16°F257249242237232228223217210

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
5,851
Cooling degree days, base 65°F
1,069
Growing degree days, base 40°F
5,617
Growing degree days, base 45°F
4,425
Growing degree days, base 50°F
3,381
Growing degree days, base 55°F
2,478
Growing degree days, base 60°F
1,709

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,11401
February93704
March749034
April4674112
May20452335
June27231654
July3364826
August7289747
September95119479
October40510165
November765024
December1,07701

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 4.8 km from Thomas County. 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 USC00141699 (Colby 1SW). Public domain.