St. Johns climate

St. Johns Frost Dates and Growing Season

NOAA 1991-2020 normals for Jacksonville Nas, 20.3 km from St. Johns, elevation 20 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Jacksonville Nas. 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 330 days.

Median at 36°F
last February 18, first December 17
Median at 32°F
last February 1, first January 5
Median at 28°F
last January 22, first January 14

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 15Mar 7Mar 2Feb 25Feb 18Feb 12Feb 6Jan 31Jan 20
32°FMar 3Feb 24Feb 15Feb 7Feb 1Jan 26Jan 19Jan 11Dec 31
28°FFeb 19Feb 7Feb 2Jan 28Jan 22Jan 17Jan 12Jan 5Dec 28
24°FFeb 6Feb 1Jan 26Jan 20Jan 17Jan 12Jan 5Jan 1Dec 21
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 20Nov 29Dec 3Dec 8Dec 17Dec 26Jan 2Jan 10Jan 22
32°FDec 3Dec 12Dec 24Dec 31Jan 5Jan 11Jan 16Jan 26Feb 6
28°FDec 19Dec 28Jan 2Jan 8Jan 14Jan 19Jan 27Feb 1Feb 12
24°FDec 15Dec 28Jan 3Jan 8Jan 15Jan 19Jan 25Jan 30Feb 5
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°F334324315308302294285276265
32°F365359349338330325315308299
28°F365365365365365361349336325
24°F365365365365365365365365359
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
99% of years
32°F or colder
80% of years
28°F or colder
43% of years
24°F or colder
13% of years
20°F or colder
2% 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
944
Cooling degree days, base 65°F
3,303
Growing degree days, base 40°F
11,489
Growing degree days, base 45°F
9,683
Growing degree days, base 50°F
7,918
Growing degree days, base 55°F
6,236
Growing degree days, base 60°F
4,688

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January29022237
February18633281
March10695459
April24198624
May1390854
June0510960
July05861,051
August05801,045
September0475925
October12285738
November9990444
December22639300

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 20.3 km from St. Johns. 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 USW00093837 (Jacksonville Nas). Public domain.