Asotin climate

Asotin Frost Dates and Growing Season

NOAA 1991-2020 normals for Lewiston Nez Perce CO AP, 4.7 km from Asotin, elevation 1436 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Lewiston Nez Perce CO AP. 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 6 and the first fall freeze around October 26, a growing season of about 200 days.

Median at 36°F
last April 29, first October 13
Median at 32°F
last April 6, first October 26
Median at 28°F
last March 15, first November 8

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 12May 7May 3May 1Apr 29Apr 25Apr 21Apr 17Apr 11
32°FApr 26Apr 19Apr 14Apr 10Apr 6Apr 3Mar 31Mar 27Mar 20
28°FApr 4Mar 30Mar 26Mar 20Mar 15Mar 11Mar 6Mar 2Feb 25
24°FMar 19Mar 10Mar 5Mar 1Feb 27Feb 22Feb 16Feb 8Jan 27
20°FMar 5Feb 28Feb 22Feb 16Feb 9Feb 1Jan 24Jan 13Jan 1
16°FFeb 27Feb 17Feb 8Jan 31Jan 23Jan 13Jan 4Dec 28Dec 12

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°FOct 1Oct 5Oct 7Oct 10Oct 13Oct 15Oct 18Oct 23Oct 28
32°FOct 10Oct 14Oct 18Oct 23Oct 26Oct 29Nov 1Nov 5Nov 12
28°FOct 20Oct 27Nov 1Nov 4Nov 8Nov 13Nov 18Nov 23Nov 28
24°FOct 30Nov 7Nov 13Nov 19Nov 23Nov 26Nov 30Dec 6Dec 13
20°FNov 10Nov 20Nov 26Nov 30Dec 5Dec 9Dec 15Dec 23Jan 3
16°FNov 23Nov 30Dec 5Dec 10Dec 16Dec 24Dec 31Jan 9Jan 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°F189182178174170166161156150
32°F225216211205200196190184176
28°F265255247241235230224218209
24°F305293285278271265257250240
20°F343330321311302294286276262
16°F365356347340332324314305290

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
98% of years
16°F or colder
86% 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
4,980
Cooling degree days, base 65°F
913
Growing degree days, base 40°F
5,581
Growing degree days, base 45°F
4,249
Growing degree days, base 50°F
3,143
Growing degree days, base 55°F
2,238
Growing degree days, base 60°F
1,499

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January89301
February71803
March608022
April407297
May18734317
June61107495
July5341801
August6322781
September76103478
October3925134
November702012
December92502

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 4.7 km from Asotin. 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 USW00024149 (Lewiston Nez Perce CO AP). Public domain.