Pacifica Frost Dates and Growing Season

NOAA 1991-2020 normals for Pacifica 4 Sse, 2.8 km from Pacifica, elevation 475 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Pacifica 4 Sse. 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 20 percent of years at Pacifica 4 Sse, so there is no typical freeze season.

Median at 36°F: last January 25, first January 4
Median at 32°F: last January 11, first January 10

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 11	Feb 27	Feb 14	Feb 1	Jan 25	Jan 16	Jan 8	Jan 2	Dec 24
32°F	Feb 12	Jan 30	Jan 26	Jan 21	Jan 11	Jan 7	Jan 4	Dec 31	Dec 23
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 1	Dec 18	Dec 25	Dec 31	Jan 4	Jan 10	Jan 19	Jan 29	Feb 19
32°F	Dec 22	Dec 28	Jan 1	Jan 5	Jan 10	Jan 16	Jan 23	Jan 26	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	364	357	350	340	327	309	294
32°F	365	365	365	365	365	365	365	365	351
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: 67% of years
32°F or colder: 20% of years
28°F or colder: 5% of years
24°F or colder: 1% 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: 2,891
Cooling degree days, base 65°F: 120
Growing degree days, base 40°F: 6,354
Growing degree days, base 45°F: 4,536
Growing degree days, base 50°F: 2,794
Growing degree days, base 55°F: 1,367
Growing degree days, base 60°F: 477

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	412	0	84
February	335	0	100
March	350	2	131
April	280	3	176
May	221	9	253
June	167	11	294
July	140	12	336
August	108	20	377
September	94	29	386
October	146	28	347
November	248	5	211
December	388	0	100

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 2.8 km from Pacifica. 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 USC00046599 (Pacifica 4 Sse). Public domain.