Roslyn climate

Roslyn Frost Dates and Growing Season

NOAA 1991-2020 normals for Cle Elum, 7.1 km from Roslyn, elevation 1900 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Cle Elum. 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 May 13 and the first fall freeze around September 25, a growing season of about 132 days.

Median at 36°F
last June 1, first September 11
Median at 32°F
last May 13, first September 25
Median at 28°F
last April 28, first October 5

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

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°FAug 31Sep 3Sep 6Sep 9Sep 11Sep 15Sep 18Sep 23Sep 27
32°FSep 11Sep 16Sep 19Sep 23Sep 25Sep 28Oct 1Oct 3Oct 7
28°FSep 20Sep 27Oct 1Oct 2Oct 5Oct 7Oct 11Oct 16Oct 23
24°FOct 2Oct 6Oct 11Oct 16Oct 20Oct 23Oct 27Nov 1Nov 7
20°FOct 16Oct 24Oct 28Nov 1Nov 5Nov 11Nov 17Nov 23Dec 1
16°FOct 31Nov 5Nov 12Nov 20Nov 24Nov 29Dec 4Dec 9Dec 19

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°F12611711110610297918678
32°F152146141136132127123117110
28°F187176170165159155150145137
24°F228218210204198192185178168
20°F272260252246239233228221212
16°F309297287278272266259252242

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
100% of years
16°F or colder
100% 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
6,991
Cooling degree days, base 65°F
250
Growing degree days, base 40°F
3,620
Growing degree days, base 45°F
2,594
Growing degree days, base 50°F
1,759
Growing degree days, base 55°F
1,084
Growing degree days, base 60°F
578

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,12800
February92000
March82601
April597023
May3684142
June19525284
July54113524
August5593504
September23115245
October594036
November88700
December1,13800

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 7.1 km from Roslyn. 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 USC00451504 (Cle Elum). Public domain.