Anchorage Municipality climate

Anchorage Municipality Frost Dates and Growing Season

NOAA 1991-2020 normals for Eagle Rvr Nature Ctr, 7.6 km from Anchorage Municipality, elevation 520 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Eagle Rvr Nature Ctr. 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 16 and the first fall freeze around September 20, a growing season of about 125 days.

Median at 36°F
last May 31, first September 6
Median at 32°F
last May 16, first September 20
Median at 28°F
last May 1, first October 1

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°FJul 2Jun 13Jun 7Jun 3May 31May 29May 26May 23May 19
32°FJun 9May 29May 23May 19May 16May 13May 10May 7May 2
28°FMay 15May 10May 6May 3May 1Apr 29Apr 26Apr 21Apr 16
24°FApr 30Apr 27Apr 23Apr 20Apr 16Apr 14Apr 10Apr 8Apr 5
20°FApr 22Apr 16Apr 13Apr 10Apr 7Apr 5Apr 3Apr 1Mar 28
16°FApr 16Apr 10Apr 6Apr 4Apr 2Apr 1Mar 29Mar 24Mar 18

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 21Aug 27Sep 1Sep 3Sep 6Sep 10Sep 13Sep 17Sep 22
32°FSep 4Sep 10Sep 14Sep 17Sep 20Sep 22Sep 25Sep 28Oct 3
28°FSep 18Sep 23Sep 26Sep 29Oct 1Oct 4Oct 7Oct 11Oct 16
24°FSep 29Oct 2Oct 5Oct 9Oct 12Oct 14Oct 17Oct 20Oct 23
20°FOct 6Oct 10Oct 14Oct 17Oct 19Oct 21Oct 24Oct 27Nov 2
16°FOct 13Oct 17Oct 20Oct 23Oct 26Oct 28Nov 1Nov 5Nov 10

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°F1181101051019792877866
32°F14513813312912512011510898
28°F174167162158154150145140132
24°F195189184181177173169165156
20°F212205201198194191187182175
16°F226218213210206203199194188

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
10,764
Cooling degree days, base 65°F
5
Growing degree days, base 40°F
1,941
Growing degree days, base 45°F
1,180
Growing degree days, base 50°F
587
Growing degree days, base 55°F
214
Growing degree days, base 60°F
49

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,59200
February1,26600
March1,24000
April84601
May563024
June3152150
July2303238
August3200154
September552019
October96401
November1,36000
December1,51600

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 7.6 km from Anchorage Municipality. 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 USC00502642 (Eagle Rvr Nature Ctr). Public domain.