Saint Johns County climate

Saint Johns County Frost Dates and Growing Season

NOAA 1991-2020 normals for St Augustine Lighthouse, 12.1 km from Saint Johns County, elevation 12 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for St Augustine Lighthouse. 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 February 1 and the first fall freeze around January 5, a growing season of about 334 days.

Median at 36°F
last February 17, first December 20
Median at 32°F
last February 1, first January 5
Median at 28°F
last January 25, first January 10

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°FMar 13Mar 6Feb 28Feb 22Feb 17Feb 10Feb 4Jan 30Jan 14
32°FMar 3Feb 24Feb 15Feb 7Feb 1Jan 27Jan 17Jan 9Dec 31
28°FFeb 22Feb 11Feb 4Jan 30Jan 25Jan 15Jan 7Jan 1Dec 26
24°FFeb 18Feb 9Feb 4Jan 31Jan 27Jan 15Jan 10Jan 3Dec 27
20°F–––––––––
16°F–––––––––

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°FNov 27Dec 3Dec 7Dec 12Dec 20Dec 27Jan 3Jan 9Jan 20
32°FDec 7Dec 17Dec 26Jan 1Jan 5Jan 10Jan 17Jan 27Feb 10
28°FDec 16Dec 24Dec 31Jan 4Jan 10Jan 19Jan 27Feb 2Feb 13
24°FDec 26Jan 1Jan 7Jan 11Jan 19Jan 29Feb 4Feb 9Feb 16
20°F–––––––––
16°F–––––––––

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°F337326317310304297291282271
32°F365362352342334326317308297
28°F365365365365365362352339323
24°F365365365365365365365365356
20°F365365365365365365365365365
16°F365365365365365365365365365

How often it gets that cold

The share of years with at least one night at or below each temperature.

36°F or colder
98% of years
32°F or colder
79% of years
28°F or colder
41% of years
24°F or colder
12% of years
20°F or colder
1% of years
16°F or colder
0% 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
803
Cooling degree days, base 65°F
3,079
Growing degree days, base 40°F
11,405
Growing degree days, base 45°F
9,592
Growing degree days, base 50°F
7,809
Growing degree days, base 55°F
6,095
Growing degree days, base 60°F
4,503

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January24821264
February16827288
March9277453
April20176606
May1350814
June0464914
July05391,004
August0529994
September0457907
October9292749
November73109488
December19139329

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 12.1 km from Saint Johns County. 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 USC00087826 (St Augustine Lighthouse). Public domain.