Butte County Frost Dates and Growing Season

NOAA 1991-2020 normals for Paradise, 9.9 km from Butte County, elevation 1750 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Paradise. 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 February 7 and the first fall freeze around December 18, a growing season of about 313 days.

Median at 36°F: last March 31, first November 29
Median at 32°F: last February 7, first December 18
Median at 28°F: last January 5, first December 31

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 27	Apr 18	Apr 12	Apr 6	Mar 31	Mar 23	Mar 12	Feb 28	Feb 17
32°F	Apr 1	Mar 10	Mar 1	Feb 18	Feb 7	Jan 29	Jan 19	Jan 8	Dec 27
28°F	Feb 14	Jan 30	Jan 18	Jan 11	Jan 5	Dec 31	Dec 27	Dec 18	Dec 11
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 11	Nov 17	Nov 21	Nov 25	Nov 29	Dec 2	Dec 6	Dec 11	Dec 18
32°F	Nov 26	Dec 3	Dec 8	Dec 13	Dec 18	Dec 25	Dec 31	Jan 7	Jan 27
28°F	Dec 8	Dec 13	Dec 19	Dec 27	Dec 31	Jan 4	Jan 12	Jan 20	Feb 9
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	291	273	260	251	242	234	227	218	206
32°F	360	346	334	323	313	303	290	275	259
28°F	365	365	365	365	365	365	362	348	334
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: 92% of years
28°F or colder: 35% of years
24°F or colder: 5% 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: 2,842
Cooling degree days, base 65°F: 1,574
Growing degree days, base 40°F: 7,881
Growing degree days, base 45°F: 6,176
Growing degree days, base 50°F: 4,682
Growing degree days, base 55°F: 3,436
Growing degree days, base 60°F: 2,411

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	546	0	43
February	444	0	63
March	391	3	135
April	265	19	227
May	120	97	446
June	26	253	677
July	1	439	904
August	1	399	863
September	13	272	709
October	107	87	448
November	363	5	138
December	566	0	29

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 9.9 km from Butte County. 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 USC00046685 (Paradise). Public domain.