Tiburon Frost Dates and Growing Season

NOAA 1991-2020 normals for Richmond, 8.6 km from Tiburon, elevation 20 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Richmond. 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 22 percent of years at Richmond, so there is no typical freeze season.

Median at 36°F: last January 17, first December 24
Median at 32°F: last January 4, first January 2

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 23	Feb 8	Jan 30	Jan 23	Jan 17	Jan 11	Jan 4	Dec 31	Dec 22
32°F	Jan 26	Jan 18	Jan 14	Jan 7	Jan 4	Jan 2	Dec 30	Dec 24	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	Dec 2	Dec 9	Dec 14	Dec 19	Dec 24	Dec 30	Jan 3	Jan 10	Jan 21
32°F	Dec 11	Dec 18	Dec 27	Dec 30	Jan 2	Jan 4	Jan 9	Jan 15	Jan 22
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	357	350	343	336	329	319	306
32°F	365	365	365	365	365	365	365	365	354
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: 80% of years
32°F or colder: 22% of years
28°F or colder: 0% 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: 2,459
Cooling degree days, base 65°F: 217
Growing degree days, base 40°F: 6,884
Growing degree days, base 45°F: 5,067
Growing degree days, base 50°F: 3,322
Growing degree days, base 55°F: 1,826
Growing degree days, base 60°F: 747

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	429	0	70
February	319	0	114
March	289	2	184
April	211	8	248
May	156	17	326
June	89	29	390
July	85	23	403
August	65	35	436
September	48	62	464
October	93	39	411
November	251	3	206
December	425	0	72

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 8.6 km from Tiburon. 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 USC00047414 (Richmond). Public domain.