Coulee Dam climate

Coulee Dam Frost Dates and Growing Season

NOAA 1991-2020 normals for Coulee Dam 1 Sw, 2.1 km from Coulee Dam, elevation 1719 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Coulee Dam 1 Sw. 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 22 and the first fall freeze around October 21, a growing season of about 180 days.

Median at 36°F
last May 5, first October 8
Median at 32°F
last April 22, first October 21
Median at 28°F
last April 1, first November 1

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 21May 15May 11May 8May 5May 2Apr 30Apr 27Apr 21
32°FMay 7May 2Apr 29Apr 25Apr 22Apr 19Apr 15Apr 11Apr 5
28°FApr 19Apr 13Apr 8Apr 4Apr 1Mar 30Mar 26Mar 22Mar 14
24°FApr 2Mar 27Mar 22Mar 17Mar 13Mar 10Mar 7Mar 4Feb 28
20°FMar 16Mar 10Mar 5Mar 3Feb 28Feb 25Feb 21Feb 16Feb 7
16°FMar 5Mar 1Feb 26Feb 21Feb 17Feb 11Feb 5Jan 31Jan 15

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 27Oct 1Oct 3Oct 5Oct 8Oct 11Oct 14Oct 18Oct 24
32°FOct 6Oct 12Oct 16Oct 18Oct 21Oct 24Oct 27Oct 31Nov 5
28°FOct 18Oct 23Oct 27Oct 30Nov 1Nov 4Nov 8Nov 12Nov 17
24°FOct 28Nov 1Nov 6Nov 9Nov 13Nov 16Nov 20Nov 23Nov 29
20°FNov 5Nov 11Nov 16Nov 20Nov 23Nov 27Dec 1Dec 6Dec 15
16°FNov 16Nov 23Nov 27Dec 1Dec 5Dec 11Dec 17Dec 25Jan 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°F173167163159156152149144136
32°F202195189185180177173168161
28°F236229223218214209204198189
24°F267258252248243238232226220
20°F297287281275270265259253244
16°F329316308302294288282275265

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
99% 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
6,151
Cooling degree days, base 65°F
689
Growing degree days, base 40°F
4,841
Growing degree days, base 45°F
3,694
Growing degree days, base 50°F
2,717
Growing degree days, base 55°F
1,892
Growing degree days, base 60°F
1,211

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,14700
February91300
March74104
April476063
May22719268
June8481447
July10273728
August11246701
September10867412
October462193
November84102
December1,13100

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 2.1 km from Coulee Dam. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00451767 (Coulee Dam 1 Sw). Public domain.