Marrowstone climate

Marrowstone Frost Dates and Growing Season

NOAA 1991-2020 normals for Port Townsend, 8.7 km from Marrowstone, elevation 100 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Port Townsend. 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 1 and the first fall freeze around November 28, a growing season of about 274 days.

Median at 36°F
last March 31, first November 9
Median at 32°F
last March 1, first November 28
Median at 28°F
last February 1, first December 19

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 16Apr 9Apr 3Mar 31Mar 28Mar 23Mar 18Mar 10
32°FMar 23Mar 15Mar 10Mar 6Mar 1Feb 26Feb 21Feb 15Feb 3
28°FMar 3Feb 24Feb 18Feb 11Feb 1Jan 21Jan 11Jan 2Dec 14
24°FFeb 20Feb 3Jan 21Jan 13Jan 4Dec 28Dec 15Dec 8Dec 1
20°FJan 18Jan 9Dec 25Dec 15Dec 9Dec 5Dec 1Nov 25Nov 19
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 19Oct 27Nov 1Nov 5Nov 9Nov 13Nov 16Nov 21Nov 26
32°FNov 9Nov 14Nov 19Nov 23Nov 28Dec 1Dec 9Dec 17Dec 26
28°FNov 20Nov 28Dec 3Dec 11Dec 19Dec 27Jan 3Jan 15Feb 6
24°FNov 23Dec 1Dec 7Dec 13Dec 24Jan 1Jan 12Jan 24Feb 12
20°FNov 19Nov 23Nov 30Dec 3Dec 8Dec 11Dec 21Jan 1Jan 14
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°F249239232227221214208201191
32°F309297288281274268261253243
28°F365355343333324316309301285
24°F365365365365365361347334321
20°F365365365365365365365365364
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
88% of years
24°F or colder
46% of years
20°F or colder
13% of years
16°F or colder
1% 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
4,837
Cooling degree days, base 65°F
61
Growing degree days, base 40°F
4,444
Growing degree days, base 45°F
2,895
Growing degree days, base 50°F
1,712
Growing degree days, base 55°F
864
Growing degree days, base 60°F
302

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January70102
February60302
March583011
April440051
May3061165
June1758284
July9224397
August7623412
September1705285
October395093
November57909
December71801

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 8.7 km from Marrowstone. 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 USC00456678 (Port Townsend). Public domain.