Brooks climate

Brooks Frost Dates and Growing Season

NOAA 1991-2020 normals for Belfast, 20.2 km from Brooks, elevation 20 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Belfast. 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 7 and the first fall freeze around October 5, a growing season of about 151 days.

Median at 36°F
last May 21, first September 27
Median at 32°F
last May 7, first October 5
Median at 28°F
last April 27, first October 19

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 1May 28May 26May 23May 21May 18May 15May 12May 9
32°FMay 21May 16May 13May 10May 7May 5May 3Apr 30Apr 28
28°FMay 6May 3May 1Apr 29Apr 27Apr 25Apr 22Apr 19Apr 13
24°FApr 26Apr 22Apr 19Apr 16Apr 13Apr 10Apr 7Apr 5Apr 1
20°FApr 15Apr 9Apr 7Apr 4Apr 3Apr 1Mar 30Mar 26Mar 20
16°FApr 5Apr 2Mar 31Mar 29Mar 25Mar 21Mar 18Mar 15Mar 12

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 15Sep 19Sep 22Sep 25Sep 27Sep 29Oct 1Oct 4Oct 8
32°FSep 24Sep 29Oct 1Oct 3Oct 5Oct 8Oct 11Oct 15Oct 20
28°FOct 3Oct 8Oct 12Oct 15Oct 19Oct 22Oct 26Oct 31Nov 3
24°FOct 17Oct 23Oct 27Oct 31Nov 2Nov 5Nov 7Nov 12Nov 16
20°FNov 1Nov 4Nov 9Nov 12Nov 14Nov 18Nov 21Nov 24Nov 29
16°FNov 11Nov 16Nov 20Nov 23Nov 25Nov 28Dec 1Dec 3Dec 8

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°F145140135131128125120116111
32°F167162158154151147144139133
28°F193187182178174170166162156
24°F221214209205202198194190182
20°F244237233229226222218214208
16°F263258252248245242238235228

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
7,785
Cooling degree days, base 65°F
204
Growing degree days, base 40°F
3,635
Growing degree days, base 45°F
2,645
Growing degree days, base 50°F
1,802
Growing degree days, base 55°F
1,110
Growing degree days, base 60°F
568

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,40000
February1,20500
March1,08301
April711011
May4033113
June14727332
July3288521
August4069494
September20317271
October538054
November83405
December1,18900

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 20.2 km from Brooks. 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 USC00170480 (Belfast). Public domain.