Juneau climate

Juneau Frost Dates and Growing Season

NOAA 1991-2020 normals for Juneau Dwtn, 0.6 km from Juneau, elevation 50 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Juneau Dwtn. 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 20 and the first fall freeze around October 22, a growing season of about 183 days.

Median at 36°F
last May 7, first October 6
Median at 32°F
last April 20, first October 22
Median at 28°F
last April 2, first November 8

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 24May 18May 14May 10May 7May 3May 1Apr 28Apr 24
32°FMay 5Apr 30Apr 26Apr 23Apr 20Apr 17Apr 14Apr 10Apr 5
28°FApr 16Apr 12Apr 8Apr 5Apr 2Mar 31Mar 29Mar 24Mar 17
24°FApr 3Mar 30Mar 26Mar 23Mar 20Mar 16Mar 13Mar 8Mar 2
20°FMar 26Mar 21Mar 17Mar 13Mar 10Mar 5Mar 1Feb 22Feb 7
16°FMar 18Mar 12Mar 6Mar 1Feb 25Feb 15Feb 7Jan 31Jan 15

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°FSep 23Sep 28Oct 1Oct 3Oct 6Oct 9Oct 12Oct 16Oct 20
32°FOct 5Oct 11Oct 15Oct 18Oct 22Oct 25Oct 28Nov 1Nov 7
28°FOct 21Oct 28Nov 1Nov 4Nov 8Nov 11Nov 16Nov 21Nov 26
24°FNov 6Nov 11Nov 16Nov 19Nov 22Nov 26Nov 30Dec 5Dec 13
20°FNov 16Nov 21Nov 25Nov 30Dec 3Dec 8Dec 15Dec 24Jan 2
16°FNov 21Nov 29Dec 3Dec 9Dec 17Dec 25Jan 1Jan 10Jan 25

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°F173165160156152148143138130
32°F205198192187183179174170162
28°F241233227222218214209203194
24°F274264258252245241237231222
20°F304293284277270264259252244
16°F340326313304297290283274261

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
97% 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
7,827
Cooling degree days, base 65°F
12
Growing degree days, base 40°F
2,459
Growing degree days, base 45°F
1,496
Growing degree days, base 50°F
750
Growing degree days, base 55°F
274
Growing degree days, base 60°F
74

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,07600
February91800
March94600
April68404
May459172
June2864173
July2425229
August2602209
September417059
October66204
November87000
December1,00800

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 0.6 km from Juneau. 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 USC00504094 (Juneau Dwtn). Public domain.