Jupiter Island Frost Dates and Growing Season

NOAA 1991-2020 normals for Port Salerno 5W, 17.7 km from Jupiter Island, elevation 12 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Port Salerno 5W. 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 33 percent of years at Port Salerno 5W, so there is no typical freeze season.

Median at 36°F: last February 3, first January 12
Median at 32°F: last January 26, 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	Mar 3	Feb 23	Feb 15	Feb 8	Feb 3	Jan 31	Jan 22	Jan 12	Jan 3
32°F	Feb 18	Feb 6	Feb 1	Jan 31	Jan 26	Jan 18	Jan 12	Jan 8	Jan 1
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 22	Dec 28	Jan 2	Jan 7	Jan 12	Jan 20	Jan 28	Feb 3	Feb 13
32°F	Dec 26	Jan 2	Jan 7	Jan 10	Jan 15	Jan 23	Jan 29	Feb 2	Feb 10
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	362	351	337	331	324	315	305
32°F	365	365	365	365	365	365	364	346	333
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: 71% of years
32°F or colder: 33% of years
28°F or colder: 8% 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: 337
Cooling degree days, base 65°F: 3,528
Growing degree days, base 40°F: 12,317
Growing degree days, base 45°F: 10,494
Growing degree days, base 50°F: 8,678
Growing degree days, base 55°F: 6,884
Growing degree days, base 60°F: 5,149

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	113	71	430
February	75	89	436
March	41	139	563
April	8	228	671
May	0	357	822
June	0	456	906
July	0	515	980
August	0	538	1,003
September	0	464	914
October	2	368	831
November	22	190	618
December	76	115	507

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 17.7 km from Jupiter Island. 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 USC00087304 (Port Salerno 5W). Public domain.