Clewiston Frost Dates and Growing Season

NOAA 1991-2020 normals for Clewiston #2, 11.6 km from Clewiston, elevation 18 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Clewiston #2. 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 January 27 and the first fall freeze around January 13, a growing season of about 357 days.

Median at 36°F: last February 7, first January 3
Median at 32°F: last January 27, first January 13
Median at 28°F: last January 18, first January 11

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 9	Mar 1	Feb 22	Feb 15	Feb 7	Feb 1	Jan 27	Jan 19	Jan 8
32°F	Feb 27	Feb 13	Feb 5	Jan 31	Jan 27	Jan 21	Jan 15	Jan 9	Jan 1
28°F	Feb 6	Jan 31	Jan 29	Jan 23	Jan 18	Jan 11	Jan 8	Jan 5	Jan 1
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 1	Dec 11	Dec 22	Dec 30	Jan 3	Jan 8	Jan 14	Jan 22	Feb 3
32°F	Dec 21	Dec 31	Jan 3	Jan 7	Jan 13	Jan 18	Jan 25	Feb 2	Feb 14
28°F	Dec 29	Jan 2	Jan 5	Jan 8	Jan 11	Jan 16	Jan 22	Jan 30	Feb 1
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	364	349	337	332	325	316	309	302	291
32°F	365	365	365	365	357	347	337	332	316
28°F	365	365	365	365	365	365	365	363	346
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: 90% of years
32°F or colder: 54% of years
28°F or colder: 18% of years
24°F or colder: 3% 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: 403
Cooling degree days, base 65°F: 3,698
Growing degree days, base 40°F: 12,421
Growing degree days, base 45°F: 10,600
Growing degree days, base 50°F: 8,786
Growing degree days, base 55°F: 7,003
Growing degree days, base 60°F: 5,290

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	146	63	392
February	74	97	443
March	43	148	571
April	10	256	696
May	0	400	865
June	0	485	935
July	0	547	1,012
August	0	550	1,015
September	0	493	944
October	3	381	843
November	27	186	609
December	101	93	462

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 11.6 km from Clewiston. 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 USC00081651 (Clewiston #2). Public domain.