Mountain Brook climate

Mountain Brook Frost Dates and Growing Season

NOAA 1991-2020 normals for Birmingham AP, 7.2 km from Mountain Brook, elevation 615 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Birmingham 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 March 21 and the first fall freeze around November 11, a growing season of about 236 days.

Median at 36°F
last April 3, first November 2
Median at 32°F
last March 21, first November 11
Median at 28°F
last March 7, first November 24

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°FApr 20Apr 14Apr 10Apr 6Apr 3Mar 31Mar 28Mar 23Mar 16
32°FApr 8Apr 2Mar 30Mar 26Mar 21Mar 17Mar 13Mar 6Feb 28
28°FMar 26Mar 20Mar 15Mar 11Mar 7Mar 2Feb 27Feb 21Feb 14
24°FMar 14Mar 8Mar 2Feb 26Feb 20Feb 15Feb 9Feb 2Jan 26
20°FMar 5Feb 27Feb 19Feb 11Feb 4Jan 31Jan 26Jan 17Jan 5
16°FFeb 28Feb 13Feb 3Jan 31Jan 26Jan 20Jan 15Jan 8Jan 2

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°FOct 21Oct 26Oct 29Oct 31Nov 2Nov 4Nov 7Nov 10Nov 17
32°FOct 30Nov 3Nov 6Nov 8Nov 11Nov 15Nov 19Nov 23Dec 1
28°FNov 6Nov 11Nov 15Nov 20Nov 24Nov 28Dec 2Dec 6Dec 15
24°FNov 16Nov 23Nov 30Dec 4Dec 9Dec 16Dec 24Jan 1Jan 9
20°FDec 1Dec 9Dec 20Dec 26Jan 1Jan 4Jan 9Jan 16Jan 31
16°FDec 17Dec 29Jan 1Jan 6Jan 10Jan 16Jan 21Jan 28Feb 7

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°F234227221217212208204200192
32°F262254246242236231225220211
28°F293282274269262257251244235
24°F328314306298291285278270258
20°F361346337331323315305299287
16°F365365365361350342334324307

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
99% of years
20°F or colder
92% of years
16°F or colder
65% 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
2,533
Cooling degree days, base 65°F
2,177
Growing degree days, base 40°F
8,908
Growing degree days, base 45°F
7,270
Growing degree days, base 50°F
5,764
Growing degree days, base 55°F
4,405
Growing degree days, base 60°F
3,205

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January631265
February459494
March30123236
April11774412
May21223667
June0399849
July0513978
August0494959
September6324768
October105104468
November34414180
December550488

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 7.2 km from Mountain Brook. 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 USW00013876 (Birmingham AP). Public domain.