Northridge Frost Dates and Growing Season

NOAA 1991-2020 normals for Northridge Cal State, 2.2 km from Northridge, elevation 904 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Northridge Cal State. 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 18 percent of years at Northridge Cal State, so there is no typical freeze season.

Median at 36°F: last January 22, first December 25
Median at 32°F: last January 2, 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	Mar 1	Feb 20	Feb 10	Jan 31	Jan 22	Jan 12	Jan 4	Dec 28	Dec 16
32°F	Jan 27	Jan 16	Jan 10	Jan 7	Jan 2	Dec 31	Dec 25	Dec 16	Dec 10
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 30	Dec 7	Dec 13	Dec 19	Dec 25	Dec 31	Jan 6	Jan 19	Feb 4
32°F	Dec 9	Dec 15	Dec 21	Dec 30	Jan 1	Jan 5	Jan 9	Jan 14	Jan 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	365	365	360	351	343	334	324	311	297
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: 74% of years
32°F or colder: 18% 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: 1,273
Cooling degree days, base 65°F: 1,711
Growing degree days, base 40°F: 9,563
Growing degree days, base 45°F: 7,742
Growing degree days, base 50°F: 5,956
Growing degree days, base 55°F: 4,288
Growing degree days, base 60°F: 2,849

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	262	13	233
February	229	14	213
March	177	25	317
April	111	56	395
May	50	103	518
June	6	207	651
July	0	369	834
August	0	405	870
September	3	321	768
October	31	148	583
November	126	44	368
December	279	8	207

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 2.2 km from Northridge. 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 USC00046263 (Northridge Cal State). Public domain.