Point MacKenzie climate

Point MacKenzie Frost Dates and Growing Season

NOAA 1991-2020 normals for Anchorage Merrill Fld, 17.2 km from Point MacKenzie, elevation 138 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Anchorage Merrill Fld. 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 1 and the first fall freeze around September 29, a growing season of about 150 days.

Median at 36°F
last May 12, first September 20
Median at 32°F
last May 1, first September 29
Median at 28°F
last April 19, first October 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 23May 19May 16May 14May 12May 10May 8May 5May 2
32°FMay 9May 6May 4May 3May 1Apr 29Apr 27Apr 23Apr 19
28°FMay 1Apr 28Apr 24Apr 22Apr 19Apr 17Apr 15Apr 13Apr 10
24°FApr 24Apr 19Apr 15Apr 13Apr 10Apr 8Apr 6Apr 4Apr 1
20°FApr 19Apr 12Apr 9Apr 6Apr 4Apr 3Apr 1Mar 30Mar 25
16°FApr 12Apr 8Apr 5Apr 3Apr 1Mar 30Mar 27Mar 23Mar 17

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 7Sep 11Sep 15Sep 17Sep 20Sep 22Sep 24Sep 27Sep 30
32°FSep 17Sep 21Sep 24Sep 27Sep 29Oct 1Oct 4Oct 7Oct 12
28°FSep 27Oct 1Oct 3Oct 6Oct 8Oct 12Oct 14Oct 17Oct 21
24°FOct 3Oct 8Oct 11Oct 15Oct 18Oct 20Oct 23Oct 25Oct 31
20°FOct 11Oct 17Oct 20Oct 23Oct 25Oct 28Oct 31Nov 4Nov 9
16°FOct 19Oct 24Oct 26Oct 30Nov 1Nov 4Nov 8Nov 11Nov 18

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°F144139136132129126123118113
32°F167161157154150147145141135
28°F188183179175172168165162156
24°F205200196193189185182178172
20°F220214210206203199195191185
16°F233227222218214210207203196

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
9,902
Cooling degree days, base 65°F
20
Growing degree days, base 40°F
2,475
Growing degree days, base 45°F
1,648
Growing degree days, base 50°F
958
Growing degree days, base 55°F
431
Growing degree days, base 60°F
122

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,53800
February1,25500
March1,22000
April78801
May473055
June2234232
July13112346
August2054264
September456057
October88702
November1,27000
December1,45700

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 17.2 km from Point MacKenzie. 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 USW00026409 (Anchorage Merrill Fld). Public domain.