Sitka climate

Sitka Frost Dates and Growing Season

NOAA 1991-2020 normals for Sitka 1 Ne, 0.6 km from Sitka, elevation 78 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Sitka 1 Ne. 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 3 and the first fall freeze around October 18, a growing season of about 166 days.

Median at 36°F
last May 23, first October 2
Median at 32°F
last May 3, first October 18
Median at 28°F
last April 7, first November 10

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 4May 31May 29May 27May 23May 20May 17May 12May 6
32°FMay 19May 14May 10May 7May 3Apr 30Apr 27Apr 23Apr 16
28°FApr 30Apr 22Apr 15Apr 12Apr 7Apr 3Mar 31Mar 26Mar 16
24°FApr 5Mar 30Mar 24Mar 20Mar 15Mar 12Mar 7Mar 2Feb 21
20°FMar 19Mar 13Mar 8Mar 3Feb 28Feb 20Feb 12Feb 1Jan 16
16°FMar 12Mar 5Feb 28Feb 21Feb 13Feb 2Jan 24Jan 14Jan 3

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 20Sep 25Sep 28Oct 1Oct 2Oct 5Oct 8Oct 12Oct 22
32°FOct 1Oct 5Oct 10Oct 14Oct 18Oct 22Oct 27Nov 1Nov 7
28°FOct 19Oct 27Nov 1Nov 5Nov 10Nov 14Nov 19Nov 24Dec 2
24°FNov 5Nov 13Nov 19Nov 24Nov 29Dec 4Dec 8Dec 16Dec 26
20°FNov 17Nov 27Dec 3Dec 9Dec 16Dec 23Dec 31Jan 6Jan 21
16°FNov 28Dec 7Dec 21Dec 29Jan 3Jan 8Jan 15Jan 26Feb 16

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°F155147141136132128124120114
32°F194184177171166162157150143
28°F245232225219212208201194181
24°F294281272265258250243235224
20°F337324310302293286279269257
16°F365360341332321311302294283

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
98% of years
16°F or colder
88% 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
7,888
Cooling degree days, base 65°F
0
Growing degree days, base 40°F
2,153
Growing degree days, base 45°F
1,185
Growing degree days, base 50°F
491
Growing degree days, base 55°F
104
Growing degree days, base 60°F
7

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January98700
February86100
March90700
April71101
May566016
June402067
July3070160
August2890177
September410064
October65306
November83700
December95900

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 Sitka. 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 USW00025379 (Sitka 1 Ne). Public domain.