Girdwood climate

Girdwood Frost Dates and Growing Season

NOAA 1991-2020 normals for Alyeska, 3.4 km from Girdwood, elevation 272 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Alyeska. 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 8 and the first fall freeze around September 29, a growing season of about 142 days.

Median at 36°F
last May 24, first September 17
Median at 32°F
last May 8, first September 29
Median at 28°F
last April 26, first October 11

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 5Jun 1May 29May 27May 24May 22May 18May 15May 12
32°FMay 22May 17May 14May 11May 8May 6May 3May 1Apr 26
28°FMay 7May 3May 1Apr 29Apr 26Apr 23Apr 19Apr 16Apr 12
24°FApr 28Apr 22Apr 18Apr 15Apr 12Apr 9Apr 6Apr 4Mar 31
20°FApr 20Apr 14Apr 10Apr 7Apr 4Apr 3Mar 31Mar 29Mar 22
16°FApr 14Apr 7Apr 4Apr 2Mar 31Mar 28Mar 25Mar 20Mar 13

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 1Sep 6Sep 10Sep 14Sep 17Sep 20Sep 23Sep 26Sep 30
32°FSep 14Sep 19Sep 23Sep 26Sep 29Oct 1Oct 4Oct 7Oct 13
28°FSep 27Oct 1Oct 4Oct 7Oct 11Oct 14Oct 17Oct 20Oct 26
24°FOct 5Oct 11Oct 15Oct 19Oct 21Oct 25Oct 28Nov 1Nov 6
20°FOct 15Oct 21Oct 25Oct 28Oct 31Nov 2Nov 6Nov 11Nov 17
16°FOct 24Oct 29Nov 1Nov 5Nov 8Nov 13Nov 16Nov 20Nov 26

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°F13112612111711310910610194
32°F161154149145142137133130124
28°F189182177172169165161156149
24°F212205200196192188183178171
20°F232224218214210206201196188
16°F248238233228223219214209202

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
9,565
Cooling degree days, base 65°F
6
Growing degree days, base 40°F
2,037
Growing degree days, base 45°F
1,254
Growing degree days, base 50°F
643
Growing degree days, base 55°F
232
Growing degree days, base 60°F
51

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,33500
February1,11000
March1,15900
April83700
May583022
June3241142
July2193250
August2791192
September494036
October83902
November1,12600
December1,26200

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 3.4 km from Girdwood. 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 USC00500243 (Alyeska). Public domain.