Mattawa climate

Mattawa Frost Dates and Growing Season

NOAA 1991-2020 normals for Priest Rapids Dam, 10.2 km from Mattawa, elevation 428 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Priest Rapids Dam. 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 March 24 and the first fall freeze around November 4, a growing season of about 222 days.

Median at 36°F
last April 9, first October 25
Median at 32°F
last March 24, first November 4
Median at 28°F
last March 5, first November 16

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°FApr 26Apr 20Apr 16Apr 12Apr 9Apr 6Apr 3Mar 31Mar 27
32°FApr 7Apr 3Mar 31Mar 28Mar 24Mar 19Mar 15Mar 10Mar 4
28°FMar 25Mar 17Mar 12Mar 8Mar 5Mar 2Feb 28Feb 24Feb 17
24°FMar 9Mar 4Mar 1Feb 26Feb 22Feb 18Feb 13Feb 7Jan 27
20°FMar 1Feb 23Feb 18Feb 13Feb 7Feb 1Jan 23Jan 14Jan 2
16°FFeb 21Feb 13Feb 6Jan 31Jan 23Jan 16Jan 10Jan 2Dec 21

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 14Oct 17Oct 21Oct 23Oct 25Oct 28Oct 30Nov 2Nov 6
32°FOct 23Oct 27Oct 30Nov 1Nov 4Nov 7Nov 9Nov 14Nov 18
28°FNov 1Nov 5Nov 9Nov 12Nov 16Nov 19Nov 22Nov 26Dec 2
24°FNov 10Nov 16Nov 21Nov 25Nov 29Dec 2Dec 7Dec 13Dec 22
20°FNov 21Nov 28Dec 3Dec 7Dec 12Dec 17Dec 25Jan 1Jan 15
16°FNov 29Dec 5Dec 11Dec 17Dec 24Dec 31Jan 7Jan 16Jan 31

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°F216210205201197193187180170
32°F246237231226222218214209202
28°F276268263258253249245238228
24°F314302294287282276270262254
20°F350337328319312306297288277
16°F365363354346338331322313301

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
97% of years
16°F or colder
81% 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
4,514
Cooling degree days, base 65°F
1,273
Growing degree days, base 40°F
6,410
Growing degree days, base 45°F
5,041
Growing degree days, base 50°F
3,845
Growing degree days, base 55°F
2,825
Growing degree days, base 60°F
1,973

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January92701
February71403
March546039
April3025168
May10269433
June19193624
July1436900
August1406869
September33155572
October29410211
November659023
December91803

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 10.2 km from Mattawa. 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 USC00456747 (Priest Rapids Dam). Public domain.