Cayucos Frost Dates and Growing Season

NOAA 1991-2020 normals for Morro Bay Fire Dept, 9.5 km from Cayucos, elevation 118 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Morro Bay Fire Dept. 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 15 percent of years at Morro Bay Fire Dept, so there is no typical freeze season.

Median at 36°F: last January 21, first December 31
Median at 32°F: last January 19, first January 14

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 21	Feb 10	Feb 3	Jan 28	Jan 21	Jan 11	Jan 4	Dec 30	Dec 18
32°F	Feb 9	Feb 3	Jan 31	Jan 25	Jan 19	Jan 13	Jan 7	Jan 3	Dec 30
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 8	Dec 15	Dec 20	Dec 26	Dec 31	Jan 3	Jan 11	Jan 23	Feb 4
32°F	Dec 25	Dec 31	Jan 2	Jan 7	Jan 14	Jan 22	Jan 29	Feb 2	Feb 8
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	365	363	356	346	339	330	317
32°F	365	365	365	365	365	365	365	365	358
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: 62% of years
32°F or colder: 15% of years
28°F or colder: 3% 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: 2,194
Cooling degree days, base 65°F: 208
Growing degree days, base 40°F: 7,140
Growing degree days, base 45°F: 5,316
Growing degree days, base 50°F: 3,512
Growing degree days, base 55°F: 1,870
Growing degree days, base 60°F: 719

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	289	3	184
February	239	4	188
March	244	5	231
April	210	8	248
May	184	7	289
June	158	8	300
July	122	24	367
August	87	33	411
September	83	45	413
October	104	55	417
November	175	15	291
December	299	1	175

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 9.5 km from Cayucos. 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 USC00045866 (Morro Bay Fire Dept). Public domain.