Stevenson Ranch Frost Dates and Growing Season

NOAA 1991-2020 normals for Newhall 5NW, 1.8 km from Stevenson Ranch, elevation 1765 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Newhall 5NW. 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 37 percent of years at Newhall 5NW, so there is no typical freeze season.

Median at 36°F: last February 22, first December 19
Median at 32°F: last January 8, first January 1

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 8	Mar 27	Mar 12	Mar 1	Feb 22	Feb 7	Jan 25	Jan 5	Dec 21
32°F	Mar 10	Feb 17	Jan 26	Jan 16	Jan 8	Jan 1	Dec 29	Dec 17	Dec 8
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 23	Dec 1	Dec 8	Dec 12	Dec 19	Dec 24	Dec 28	Jan 11	Feb 8
32°F	Nov 30	Dec 10	Dec 20	Dec 28	Jan 1	Jan 4	Jan 12	Jan 25	Feb 25
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	359	345	332	317	306	293	280	266	251
32°F	365	365	365	365	365	365	363	346	329
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: 93% of years
32°F or colder: 37% of years
28°F or colder: 3% 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: 1,677
Cooling degree days, base 65°F: 1,902
Growing degree days, base 40°F: 9,352
Growing degree days, base 45°F: 7,545
Growing degree days, base 50°F: 5,822
Growing degree days, base 55°F: 4,270
Growing degree days, base 60°F: 2,953

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	319	5	185
February	296	8	155
March	222	28	283
April	161	55	348
May	66	132	532
June	12	224	662
July	0	425	889
August	0	464	928
September	6	356	799
October	49	164	580
November	183	40	315
December	365	4	146

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 1.8 km from Stevenson Ranch. 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 USC00046161 (Newhall 5NW). Public domain.