Redlands Frost Dates and Growing Season

NOAA 1991-2020 normals for Redlands, 2.4 km from Redlands, elevation 1410 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Redlands. 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 December 19, a growing season of about 329 days.

Median at 36°F: last March 2, first December 2
Median at 32°F: last January 27, first December 19
Median at 28°F: last January 7, first January 1

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	Apr 5	Mar 22	Mar 13	Mar 7	Mar 2	Feb 26	Feb 19	Feb 10	Jan 31
32°F	Feb 28	Feb 19	Feb 10	Feb 3	Jan 27	Jan 16	Jan 7	Jan 1	Dec 21
28°F	Feb 15	Feb 1	Jan 28	Jan 15	Jan 7	Jan 1	Dec 29	Dec 23	Dec 17
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	Nov 17	Nov 22	Nov 26	Nov 30	Dec 2	Dec 5	Dec 9	Dec 14	Dec 19
32°F	Dec 1	Dec 6	Dec 11	Dec 15	Dec 19	Dec 25	Jan 1	Jan 9	Jan 26
28°F	Dec 13	Dec 19	Dec 24	Dec 29	Jan 1	Jan 6	Jan 16	Jan 30	Feb 13
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	306	295	287	279	272	266	258	249	235
32°F	365	355	346	337	329	320	310	302	292
28°F	365	365	365	365	365	365	365	358	340
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: 100% of years
32°F or colder: 88% of years
28°F or colder: 26% 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: 1,647
Cooling degree days, base 65°F: 1,751
Growing degree days, base 40°F: 9,229
Growing degree days, base 45°F: 7,413
Growing degree days, base 50°F: 5,663
Growing degree days, base 55°F: 4,087
Growing degree days, base 60°F: 2,776

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	347	1	146
February	287	2	151
March	234	9	249
April	137	36	352
May	57	99	507
June	8	232	674
July	0	432	897
August	0	451	916
September	3	331	778
October	41	131	555
November	170	25	309
December	363	1	129

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 2.4 km from Redlands. 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 USC00047306 (Redlands). Public domain.