South Pasadena Frost Dates and Growing Season

NOAA 1991-2020 normals for St Petersburg, 11 km from South Pasadena, elevation 8 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for St Petersburg. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

A freeze (32°F or colder) happens in only 11 percent of years at St Petersburg, so there is no typical freeze season.

Median at 36°F: last January 22, first January 13
Median at 32°F: last January 17, first January 15

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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	Feb 14	Feb 6	Jan 31	Jan 27	Jan 22	Jan 17	Jan 11	Jan 4	Dec 28
32°F	Feb 5	Feb 1	Jan 28	Jan 21	Jan 17	Jan 12	Jan 8	Jan 3	Dec 31
28°F	–	–	–	–	–	–	–	–	–
24°F	–	–	–	–	–	–	–	–	–
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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	Dec 20	Dec 30	Jan 3	Jan 8	Jan 13	Jan 19	Jan 24	Jan 31	Feb 8
32°F	Dec 23	Jan 2	Jan 7	Jan 11	Jan 15	Jan 20	Jan 28	Jan 31	Feb 5
28°F	–	–	–	–	–	–	–	–	–
24°F	–	–	–	–	–	–	–	–	–
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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	365	365	365	365	365	361	352	339	328
32°F	365	365	365	365	365	365	365	365	357
28°F	365	365	365	365	365	365	365	365	365
24°F	365	365	365	365	365	365	365	365	365
20°F	365	365	365	365	365	365	365	365	365
16°F	365	365	365	365	365	365	365	365	365

How often it gets that cold

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

36°F or colder: 41% of years
32°F or colder: 11% of years
28°F or colder: 1% of years
24°F or colder: 0% of years
20°F or colder: 0% 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: 373
Cooling degree days, base 65°F: 3,852
Growing degree days, base 40°F: 12,603
Growing degree days, base 45°F: 10,780
Growing degree days, base 50°F: 8,965
Growing degree days, base 55°F: 7,173
Growing degree days, base 60°F: 5,447

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	139	48	381
February	76	66	412
March	36	150	580
April	4	273	719
May	0	443	908
June	0	535	986
July	0	586	1,051
August	0	587	1,052
September	0	522	972
October	2	379	842
November	26	175	599
December	90	87	465

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 11 km from South Pasadena. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00087886 (St Petersburg). Public domain.