Blythe Frost Dates and Growing Season

NOAA 1991-2020 normals for Blythe, 0.4 km from Blythe, elevation 268 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Blythe. 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 January 25 and the first fall freeze around December 12, a growing season of about 325 days.

Median at 36°F: last February 21, first December 1
Median at 32°F: last January 25, first December 12
Median at 28°F: last December 30, first December 22

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 10	Mar 4	Feb 28	Feb 25	Feb 21	Feb 16	Feb 11	Feb 4	Jan 25
32°F	Feb 24	Feb 15	Feb 8	Feb 1	Jan 25	Jan 16	Jan 9	Jan 3	Dec 29
28°F	Jan 30	Jan 12	Jan 5	Jan 1	Dec 30	Dec 26	Dec 23	Dec 18	Dec 10
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 16	Nov 22	Nov 26	Nov 29	Dec 1	Dec 3	Dec 6	Dec 11	Dec 16
32°F	Nov 28	Dec 2	Dec 5	Dec 9	Dec 12	Dec 15	Dec 20	Dec 25	Jan 3
28°F	Dec 5	Dec 10	Dec 14	Dec 18	Dec 22	Dec 25	Dec 28	Jan 1	Jan 11
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	317	305	296	289	283	277	273	265	254
32°F	353	345	338	332	325	317	308	299	287
28°F	365	365	365	365	359	354	349	342	332
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: 96% of years
28°F or colder: 62% of years
24°F or colder: 9% 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: 1,139
Cooling degree days, base 65°F: 4,251
Growing degree days, base 40°F: 12,237
Growing degree days, base 45°F: 10,418
Growing degree days, base 50°F: 8,641
Growing degree days, base 55°F: 6,988
Growing degree days, base 60°F: 5,523

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	317	1	161
February	194	7	235
March	80	64	450
April	19	221	653
May	2	482	946
June	0	699	1,149
July	0	896	1,361
August	0	880	1,345
September	0	672	1,122
October	8	281	738
November	119	47	380
December	400	0	102

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 0.4 km from Blythe. 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 USC00040924 (Blythe). Public domain.