Jefferson County climate

Jefferson County Frost Dates and Growing Season

NOAA 1991-2020 normals for Elwha RS, 26.7 km from Jefferson County, elevation 360 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Elwha RS. 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 April 9 and the first fall freeze around November 3, a growing season of about 209 days.

Median at 36°F
last May 3, first October 19
Median at 32°F
last April 9, first November 3
Median at 28°F
last March 4, first November 24

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°FMay 19May 14May 10May 6May 3Apr 30Apr 27Apr 23Apr 18
32°FApr 29Apr 22Apr 18Apr 13Apr 9Apr 4Mar 31Mar 27Mar 19
28°FMar 30Mar 23Mar 16Mar 10Mar 4Feb 28Feb 22Feb 16Feb 3
24°FFeb 28Feb 22Feb 17Feb 10Feb 1Jan 21Jan 10Jan 1Dec 13
20°FFeb 17Feb 1Jan 24Jan 16Jan 7Dec 31Dec 18Dec 10Dec 2
16°FJan 31Jan 22Jan 16Jan 10Jan 1Dec 22Dec 11Dec 7Nov 29

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 5Oct 9Oct 13Oct 16Oct 19Oct 22Oct 25Oct 28Nov 2
32°FOct 19Oct 24Oct 28Oct 31Nov 3Nov 6Nov 10Nov 16Nov 23
28°FNov 2Nov 9Nov 14Nov 20Nov 24Nov 29Dec 3Dec 10Dec 23
24°FNov 18Nov 26Dec 1Dec 7Dec 13Dec 23Dec 30Jan 8Feb 1
20°FNov 25Dec 1Dec 6Dec 11Dec 21Dec 31Jan 9Jan 22Feb 7
16°FNov 27Dec 4Dec 10Dec 17Dec 29Jan 6Jan 15Jan 19Jan 30

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°F189181177172168165159155148
32°F235227220214209205199193185
28°F307292282275268260252244232
24°F365351340331322315307297281
20°F365365365365363351342334320
16°F365365365365365365365365355

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
90% of years
20°F or colder
54% of years
16°F or colder
15% 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
6,008
Cooling degree days, base 65°F
81
Growing degree days, base 40°F
3,594
Growing degree days, base 45°F
2,370
Growing degree days, base 50°F
1,440
Growing degree days, base 55°F
742
Growing degree days, base 60°F
289

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January87000
February74800
March70402
April539026
May3641128
June2439218
July12031377
August9534405
September2156244
October511040
November72501
December87700

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 26.7 km from Jefferson County. 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 USC00452548 (Elwha RS). Public domain.