Cupertino Frost Dates and Growing Season

NOAA 1991-2020 normals for San Jose, 11.8 km from Cupertino, elevation 67 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for San Jose. 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 2 and the first fall freeze around December 25, a growing season of about 362 days.

Median at 36°F: last January 26, first December 10
Median at 32°F: last January 2, first December 25

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 27	Feb 17	Feb 7	Feb 1	Jan 26	Jan 19	Jan 10	Jan 2	Dec 27
32°F	Jan 23	Jan 16	Jan 10	Jan 6	Jan 2	Dec 31	Dec 27	Dec 22	Dec 14
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	Nov 22	Nov 30	Dec 2	Dec 6	Dec 10	Dec 14	Dec 21	Dec 28	Jan 4
32°F	Dec 4	Dec 9	Dec 14	Dec 19	Dec 25	Dec 28	Jan 1	Jan 5	Jan 14
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	350	339	334	326	318	309	302	291	278
32°F	365	365	365	365	362	356	350	343	335
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: 95% of years
32°F or colder: 56% 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: 2,040
Cooling degree days, base 65°F: 764
Growing degree days, base 40°F: 7,850
Growing degree days, base 45°F: 6,038
Growing degree days, base 50°F: 4,309
Growing degree days, base 55°F: 2,811
Growing degree days, base 60°F: 1,625

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	429	0	75
February	305	0	126
March	251	3	223
April	169	16	298
May	79	51	437
June	15	121	556
July	2	177	640
August	1	194	659
September	6	150	594
October	73	49	440
November	269	2	191
December	440	0	70

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 11.8 km from Cupertino. 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 USC00047821 (San Jose). Public domain.