Boulevard Park climate

Boulevard Park Frost Dates and Growing Season

NOAA 1991-2020 normals for Seattle Boeing Fld, 2.3 km from Boulevard Park, elevation 20 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Seattle Boeing Fld. 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 17, a growing season of about 247 days.

Median at 36°F
last April 3, first October 31
Median at 32°F
last March 13, first November 17
Median at 28°F
last February 18, first December 2

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 28Apr 20Apr 12Apr 7Apr 3Mar 31Mar 27Mar 23Mar 17
32°FApr 1Mar 25Mar 21Mar 17Mar 13Mar 9Mar 4Feb 28Feb 20
28°FMar 10Mar 3Feb 27Feb 22Feb 18Feb 11Feb 2Jan 22Jan 7
24°FFeb 23Feb 17Feb 7Jan 31Jan 17Jan 6Dec 31Dec 18Dec 7
20°FFeb 13Jan 31Jan 15Jan 1Dec 27Dec 18Dec 12Dec 7Nov 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 26Oct 29Oct 31Nov 3Nov 7Nov 11Nov 17
32°FNov 1Nov 6Nov 10Nov 13Nov 17Nov 21Nov 24Nov 29Dec 6
28°FNov 12Nov 18Nov 23Nov 27Dec 2Dec 7Dec 13Dec 20Dec 30
24°FNov 21Nov 29Dec 3Dec 8Dec 14Dec 21Dec 29Jan 7Jan 29
20°FNov 26Dec 1Dec 6Dec 12Dec 19Dec 25Jan 1Jan 14Feb 3
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°F232223218214209205198191182
32°F278266259253247242236230222
28°F334320310302295288280270260
24°F365365358348337330322313300
20°F365365365365365365359342330
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
99% of years
24°F or colder
81% of years
20°F or colder
39% of years
16°F or colder
9% 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
4,341
Cooling degree days, base 65°F
282
Growing degree days, base 40°F
5,182
Growing degree days, base 45°F
3,633
Growing degree days, base 50°F
2,392
Growing degree days, base 55°F
1,443
Growing degree days, base 60°F
737

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January69107
February59506
March555026
April400186
May23010248
June10735378
July26101539
August19104550
September9832384
October3511137
November557025
December71305

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 2.3 km from Boulevard Park. 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 USW00024234 (Seattle Boeing Fld). Public domain.