Fort Greely climate

Fort Greely Frost Dates and Growing Season

NOAA 1991-2020 normals for Big Delta AP, 2.8 km from Fort Greely, elevation 1277 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Big Delta 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 17 and the first fall freeze around September 7, a growing season of about 113 days.

Median at 36°F
last May 29, first August 27
Median at 32°F
last May 17, first September 7
Median at 28°F
last May 6, first September 20

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 9Jun 4Jun 2May 31May 29May 26May 22May 19May 15
32°FMay 31May 28May 24May 20May 17May 13May 10May 7May 3
28°FMay 24May 17May 12May 9May 6May 3May 1Apr 29Apr 23
24°FMay 12May 7May 3May 1Apr 28Apr 25Apr 22Apr 19Apr 14
20°FMay 4Apr 30Apr 26Apr 23Apr 20Apr 18Apr 15Apr 11Apr 8
16°FApr 27Apr 22Apr 19Apr 16Apr 14Apr 11Apr 9Apr 6Apr 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°FAug 13Aug 17Aug 21Aug 24Aug 27Aug 29Sep 1Sep 4Sep 9
32°FAug 23Aug 28Sep 1Sep 3Sep 7Sep 11Sep 14Sep 17Sep 22
28°FSep 3Sep 9Sep 13Sep 17Sep 20Sep 22Sep 25Sep 27Oct 1
24°FSep 13Sep 19Sep 23Sep 25Sep 27Sep 30Oct 2Oct 5Oct 10
20°FSep 21Sep 26Sep 28Oct 1Oct 3Oct 5Oct 8Oct 12Oct 16
16°FSep 26Sep 30Oct 2Oct 6Oct 8Oct 11Oct 14Oct 17Oct 21

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°F10910398949188847972
32°F13412712111811310910510093
28°F154147142137134130126119111
24°F170164160155152148144139130
20°F183177173169165162157152147
16°F194188184180177174170166159

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
12,783
Cooling degree days, base 65°F
34
Growing degree days, base 40°F
2,213
Growing degree days, base 45°F
1,487
Growing degree days, base 50°F
882
Growing degree days, base 55°F
432
Growing degree days, base 60°F
158

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January2,04400
February1,61400
March1,57600
April93503
May513064
June20912259
July14915334
August2976189
September605033
October1,19502
November1,70500
December1,94100

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 2.8 km from Fort Greely. 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 USW00026415 (Big Delta AP). Public domain.