Palouse climate

Palouse Frost Dates and Growing Season

NOAA 1991-2020 normals for Potlatch 3 Nne, 17.7 km from Palouse, elevation 2760 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Potlatch 3 Nne. 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 15 and the first fall freeze around September 21, a growing season of about 126 days.

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

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 15Aug 23Aug 27Sep 1Sep 3Sep 6Sep 10Sep 15Sep 21
32°FAug 31Sep 6Sep 12Sep 17Sep 21Sep 24Sep 27Oct 1Oct 7
28°FSep 18Sep 26Sep 30Oct 2Oct 5Oct 8Oct 13Oct 18Oct 27
24°FOct 1Oct 6Oct 10Oct 16Oct 20Oct 26Oct 30Nov 5Nov 14
20°FOct 14Oct 21Oct 27Oct 31Nov 4Nov 10Nov 16Nov 23Nov 30
16°FOct 28Nov 4Nov 11Nov 17Nov 24Nov 28Dec 3Dec 10Dec 20

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°F11210396908477706052
32°F14914213613112612111410897
28°F192180173168162156151145137
24°F234224216209203198191183171
20°F278266258251243237229221211
16°F315300291282274268261251239

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
6,804
Cooling degree days, base 65°F
222
Growing degree days, base 40°F
3,603
Growing degree days, base 45°F
2,534
Growing degree days, base 50°F
1,676
Growing degree days, base 55°F
1,009
Growing degree days, base 60°F
523

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,04200
February88100
March80902
April605025
May3882131
June23115243
July7589479
August7194488
September23622252
October564051
November83705
December1,06600

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 17.7 km from Palouse. 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 USC00107301 (Potlatch 3 Nne). Public domain.