Millbrook climate

Millbrook Frost Dates and Growing Season

NOAA 1991-2020 normals for Millbrook 3 W, 4 km from Millbrook, elevation 413 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Millbrook 3 W. 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 4 and the first fall freeze around October 7, a growing season of about 155 days.

Median at 36°F
last May 19, first September 29
Median at 32°F
last May 4, first October 7
Median at 28°F
last April 22, 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 2May 28May 25May 21May 19May 16May 11May 6May 1
32°FMay 21May 17May 12May 8May 4May 1Apr 29Apr 25Apr 21
28°FMay 9May 3Apr 30Apr 25Apr 22Apr 19Apr 16Apr 13Apr 6
24°FApr 25Apr 19Apr 15Apr 12Apr 8Apr 5Apr 2Mar 31Mar 26
20°FApr 11Apr 5Apr 2Mar 31Mar 29Mar 26Mar 22Mar 18Mar 13
16°FApr 2Mar 29Mar 25Mar 21Mar 18Mar 15Mar 12Mar 9Mar 4

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 16Sep 21Sep 25Sep 27Sep 29Oct 1Oct 3Oct 6Oct 11
32°FSep 28Oct 1Oct 3Oct 5Oct 7Oct 10Oct 13Oct 18Oct 24
28°FOct 5Oct 9Oct 12Oct 16Oct 19Oct 23Oct 27Oct 31Nov 4
24°FOct 15Oct 21Oct 26Oct 30Nov 1Nov 5Nov 8Nov 12Nov 17
20°FOct 28Nov 2Nov 7Nov 11Nov 15Nov 18Nov 22Nov 27Dec 2
16°FNov 10Nov 16Nov 21Nov 24Nov 28Dec 1Dec 4Dec 9Dec 17

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°F154146141137132128124120113
32°F176168164160155151147142135
28°F200193188183179175170165158
24°F226219214210206201195190183
20°F254245240235230226221215208
16°F279271265260255250246240233

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
6,427
Cooling degree days, base 65°F
497
Growing degree days, base 40°F
4,638
Growing degree days, base 45°F
3,512
Growing degree days, base 50°F
2,534
Growing degree days, base 55°F
1,697
Growing degree days, base 60°F
1,016

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,23500
February1,03602
March891014
April533368
May24623258
June6584470
July10188643
August22141584
September14353362
October4554111
November737019
December1,05402

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 4 km from Millbrook. 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 USW00064756 (Millbrook 3 W). Public domain.