Yukon-Koyukuk Census Area climate

Yukon-Koyukuk Census Area Frost Dates and Growing Season

NOAA 1991-2020 normals for Tanana Calhoun Mem AP, 64.9 km from Yukon-Koyukuk Census Area, elevation 227 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Tanana Calhoun Mem AP. 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 29 and the first fall freeze around August 28, a growing season of about 89 days.

Median at 32°F
last May 29, first August 28
Median at 28°F
last May 16, first September 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°F–––––––––
32°FJun 16Jun 7Jun 2May 31May 29May 26May 22May 19May 15
28°FMay 30May 26May 22May 19May 16May 13May 11May 9May 5
24°FMay 21May 16May 12May 10May 8May 6May 4May 1Apr 28
20°FMay 14May 8May 5May 3May 2Apr 30Apr 28Apr 25Apr 20
16°FMay 7May 3May 1Apr 29Apr 27Apr 24Apr 21Apr 19Apr 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°F–––––––––
32°FAug 10Aug 17Aug 22Aug 25Aug 28Aug 31Sep 1Sep 5Sep 9
28°FAug 25Aug 31Sep 2Sep 5Sep 8Sep 12Sep 17Sep 20Sep 25
24°FSep 5Sep 11Sep 16Sep 19Sep 22Sep 24Sep 27Sep 30Oct 4
20°FSep 17Sep 21Sep 24Sep 27Sep 30Oct 2Oct 5Oct 8Oct 12
16°FSep 24Sep 29Oct 2Oct 4Oct 7Oct 9Oct 12Oct 16Oct 19

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°F807268635954494336
32°F10810197938984797263
28°F13312712311811411010510193
24°F152148143139135132128122115
20°F167161157154151148144139131
16°F180174170166163160157152145

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
14,408
Cooling degree days, base 65°F
27
Growing degree days, base 40°F
1,947
Growing degree days, base 45°F
1,285
Growing degree days, base 50°F
742
Growing degree days, base 55°F
349
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
January2,30300
February1,85400
March1,81900
April1,12701
May585043
June22911241
July17514307
August3571137
September671014
October1,26000
November1,85200
December2,17800

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 64.9 km from Yukon-Koyukuk Census Area. 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 USW00026529 (Tanana Calhoun Mem AP). Public domain.