Colfax climate

Colfax Frost Dates and Growing Season

NOAA 1991-2020 normals for Pullman 2 Nw, 19 km from Colfax, elevation 2515 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Pullman 2 Nw. 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 6 and the first fall freeze around September 29, a growing season of about 143 days.

Median at 36°F
last June 1, first September 11
Median at 32°F
last May 6, first September 29
Median at 28°F
last April 19, first October 12

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°FJul 1Jun 20Jun 12Jun 7Jun 1May 28May 23May 18May 12
32°FMay 25May 18May 13May 10May 6May 3Apr 30Apr 27Apr 22
28°FMay 7May 1Apr 27Apr 23Apr 19Apr 14Apr 8Apr 2Mar 27
24°FApr 17Apr 7Apr 1Mar 28Mar 24Mar 18Mar 13Mar 7Mar 2
20°FMar 29Mar 19Mar 13Mar 8Mar 4Feb 28Feb 24Feb 16Feb 5
16°FMar 13Mar 5Feb 28Feb 24Feb 17Feb 10Feb 3Jan 25Jan 8

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°FAug 24Aug 31Sep 4Sep 7Sep 11Sep 15Sep 19Sep 23Sep 29
32°FSep 9Sep 16Sep 22Sep 27Sep 29Oct 2Oct 5Oct 9Oct 15
28°FSep 26Oct 1Oct 4Oct 7Oct 12Oct 15Oct 21Oct 26Nov 2
24°FOct 5Oct 12Oct 17Oct 23Oct 29Nov 2Nov 7Nov 14Nov 22
20°FOct 17Oct 25Nov 1Nov 7Nov 14Nov 19Nov 25Nov 29Dec 7
16°FOct 27Nov 8Nov 16Nov 24Nov 28Dec 3Dec 9Dec 15Dec 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°F1271171111049992857765
32°F168160153148143138131125116
28°F208197191185178173166160150
24°F255243235227221214206198188
20°F294280271264258249243234223
16°F331316306297288280272261247

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
6,418
Cooling degree days, base 65°F
331
Growing degree days, base 40°F
4,005
Growing degree days, base 45°F
2,889
Growing degree days, base 50°F
1,983
Growing degree days, base 55°F
1,254
Growing degree days, base 60°F
705

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,03400
February85400
March76606
April563039
May3458169
June19126290
July55123533
August49134551
September18738311
October513277
November80906
December1,05400

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 Colfax. 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 USC00456789 (Pullman 2 Nw). Public domain.