Coulee City climate

Coulee City Frost Dates and Growing Season

NOAA 1991-2020 normals for Hartline, 16.4 km from Coulee City, elevation 1906 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Hartline. 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 12, a growing season of about 162 days.

Median at 36°F
last May 23, first October 1
Median at 32°F
last May 2, first October 12
Median at 28°F
last April 16, first October 25

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 14Jun 8Jun 2May 29May 23May 18May 13May 8May 2
32°FMay 22May 15May 10May 5May 2Apr 29Apr 27Apr 22Apr 17
28°FMay 5Apr 30Apr 25Apr 20Apr 16Apr 12Apr 7Apr 2Mar 26
24°FApr 12Apr 6Apr 1Mar 27Mar 20Mar 14Mar 9Mar 5Feb 27
20°FMar 27Mar 15Mar 9Mar 4Mar 1Feb 26Feb 21Feb 14Feb 3
16°FMar 11Mar 4Feb 28Feb 22Feb 16Feb 10Feb 3Jan 26Jan 11

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 13Sep 20Sep 24Sep 28Oct 1Oct 3Oct 6Oct 9Oct 14
32°FSep 27Oct 1Oct 5Oct 9Oct 12Oct 15Oct 19Oct 23Oct 29
28°FOct 9Oct 15Oct 19Oct 22Oct 25Oct 29Nov 1Nov 5Nov 13
24°FOct 19Oct 25Oct 30Nov 2Nov 6Nov 10Nov 15Nov 19Nov 25
20°FOct 29Nov 5Nov 11Nov 16Nov 20Nov 24Nov 28Dec 3Dec 11
16°FNov 10Nov 18Nov 24Nov 28Dec 1Dec 6Dec 11Dec 19Jan 1

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°F15514513913312812311711099
32°F185177172166162157151145136
28°F220212203198192188183176167
24°F258249242235229223216208199
20°F297284275268261256248241231
16°F332317307297291284276267256

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
6,443
Cooling degree days, base 65°F
560
Growing degree days, base 40°F
4,474
Growing degree days, base 45°F
3,368
Growing degree days, base 50°F
2,437
Growing degree days, base 55°F
1,660
Growing degree days, base 60°F
1,033

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,16200
February90700
March76903
April522047
May27313224
June12156387
July18223670
August17211659
September14256370
October496178
November85801
December1,15800

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 16.4 km from Coulee City. 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 USC00453529 (Hartline). Public domain.