Downey climate

Downey Frost Dates and Growing Season

NOAA 1991-2020 normals for Downey, 0.3 km from Downey, elevation 4865 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Downey. 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 May 31 and the first fall freeze around September 18, a growing season of about 110 days.

Median at 36°F
last June 17, first September 7
Median at 32°F
last May 31, first September 18
Median at 28°F
last May 9, first October 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.

Threshold10%20%30%40%50%60%70%80%90%
36°FJun 30Jun 26Jun 23Jun 20Jun 17Jun 15Jun 12Jun 9Jun 3
32°FJun 16Jun 12Jun 7Jun 3May 31May 28May 23May 18May 13
28°FMay 31May 23May 16May 13May 9May 6May 3Apr 30Apr 23
24°FMay 8May 3Apr 30Apr 26Apr 22Apr 19Apr 15Apr 12Apr 6
20°FApr 22Apr 16Apr 10Apr 7Apr 3Mar 31Mar 28Mar 22Mar 14
16°FApr 6Mar 31Mar 27Mar 22Mar 17Mar 13Mar 9Mar 6Feb 28

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.

Threshold10%20%30%40%50%60%70%80%90%
36°FAug 23Aug 29Sep 1Sep 4Sep 7Sep 10Sep 12Sep 16Sep 21
32°FSep 3Sep 9Sep 12Sep 15Sep 18Sep 21Sep 26Sep 30Oct 5
28°FSep 15Sep 20Sep 25Sep 28Oct 1Oct 4Oct 7Oct 12Oct 17
24°FSep 28Oct 3Oct 6Oct 10Oct 15Oct 18Oct 22Oct 25Nov 1
20°FOct 10Oct 17Oct 22Oct 25Oct 27Nov 1Nov 4Nov 8Nov 14
16°FOct 24Oct 29Nov 1Nov 5Nov 9Nov 13Nov 17Nov 21Nov 26

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.

Threshold10%20%30%40%50%60%70%80%90%
36°F999187838076716657
32°F133125119114110104989385
28°F169161155150144139134128118
24°F198190184179174169164159152
20°F232223216211206201195189180
16°F262254247242236231225219211

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
100% of years
28°F or colder
100% of years
24°F or colder
100% of years
20°F or colder
100% of years
16°F or colder
100% 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
7,390
Cooling degree days, base 65°F
353
Growing degree days, base 40°F
3,880
Growing degree days, base 45°F
2,858
Growing degree days, base 50°F
2,011
Growing degree days, base 55°F
1,319
Growing degree days, base 60°F
764

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,29400
February1,06000
March89002
April618013
May3861129
June15430333
July21170613
August26129569
September20622286
October576164
November91802
December1,24300

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 0.3 km from Downey. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00102667 (Downey). Public domain.