Renton climate

Renton Frost Dates and Growing Season

NOAA 1991-2020 normals for Renton Muni AP, 1.2 km from Renton, elevation 29 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Renton Muni 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 March 13 and the first fall freeze around November 16, a growing season of about 248 days.

Median at 36°F
last April 6, first October 31
Median at 32°F
last March 13, first November 16
Median at 28°F
last February 13, first December 6

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 25Apr 18Apr 14Apr 10Apr 6Apr 2Mar 31Mar 26Mar 21
32°FMar 31Mar 25Mar 22Mar 18Mar 13Mar 8Mar 3Feb 27Feb 19
28°FMar 6Feb 28Feb 24Feb 18Feb 13Feb 8Jan 31Jan 15Jan 1
24°FFeb 22Feb 14Feb 4Jan 22Jan 8Jan 1Dec 24Dec 14Dec 3
20°FFeb 15Jan 30Jan 7Dec 30Dec 24Dec 14Dec 9Dec 4Nov 30
16°F–––––––––

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 17Oct 22Oct 25Oct 28Oct 31Nov 1Nov 5Nov 10Nov 17
32°FOct 29Nov 2Nov 7Nov 11Nov 16Nov 20Nov 25Dec 1Dec 9
28°FNov 11Nov 19Nov 25Dec 1Dec 6Dec 13Dec 21Dec 29Jan 9
24°FNov 22Nov 29Dec 4Dec 9Dec 19Dec 27Jan 2Jan 17Feb 9
20°FNov 24Dec 1Dec 4Dec 8Dec 14Dec 24Dec 30Jan 20Feb 12
16°F–––––––––

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°F231223217212207202198193186
32°F280269262254248242236231221
28°F341326315308301292282273262
24°F365365364353342334326316306
20°F365365365365365365363346331
16°F365365365365365365365365365

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
98% of years
24°F or colder
71% of years
20°F or colder
29% of years
16°F or colder
6% 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
4,390
Cooling degree days, base 65°F
258
Growing degree days, base 40°F
5,115
Growing degree days, base 45°F
3,574
Growing degree days, base 50°F
2,336
Growing degree days, base 55°F
1,396
Growing degree days, base 60°F
702

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January69606
February59805
March555025
April412176
May2378238
June11029369
July2597538
August2097543
September10626371
October3511138
November563024
December71905

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 1.2 km from Renton. 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 USW00094248 (Renton Muni AP). Public domain.