Nipomo climate

Nipomo Frost Dates and Growing Season

NOAA 1991-2020 normals for Twitchell Dam, 15.4 km from Nipomo, elevation 582 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Twitchell Dam. 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 4 and the first fall freeze around December 4, a growing season of about 301 days.

Median at 36°F
last March 31, first November 16
Median at 32°F
last February 4, first December 4
Median at 28°F
last December 31, first December 17

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°FApr 26Apr 18Apr 11Apr 6Mar 31Mar 21Mar 9Feb 28Feb 14
32°FMar 31Mar 9Feb 27Feb 14Feb 4Jan 27Jan 15Jan 6Dec 27
28°FFeb 3Jan 20Jan 10Jan 3Dec 31Dec 25Dec 20Dec 13Dec 4
24°FJan 10Jan 3Dec 31Dec 30Dec 28Dec 24Dec 21Dec 17Dec 10
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.

Threshold10%20%30%40%50%60%70%80%90%
36°FOct 21Nov 1Nov 4Nov 10Nov 16Nov 21Nov 25Dec 1Dec 6
32°FNov 14Nov 21Nov 26Dec 1Dec 4Dec 8Dec 13Dec 20Dec 28
28°FNov 26Dec 4Dec 8Dec 12Dec 17Dec 22Dec 26Jan 2Jan 14
24°FDec 7Dec 12Dec 19Dec 21Dec 25Dec 29Dec 30Jan 1Jan 9
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.

Threshold10%20%30%40%50%60%70%80%90%
36°F278264252241231223214205194
32°F343333321311301288276260244
28°F365365365359353345340334321
24°F365365365365365365365365358
20°F365365365365365365365365365
16°F365365365365365365365365365

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
98% of years
28°F or colder
66% of years
24°F or colder
13% of years
20°F or colder
3% of years
16°F or colder
1% 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
2,706
Cooling degree days, base 65°F
314
Growing degree days, base 40°F
6,739
Growing degree days, base 45°F
4,944
Growing degree days, base 50°F
3,267
Growing degree days, base 55°F
1,878
Growing degree days, base 60°F
887

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January4091100
February3511100
March3253162
April26611203
May20620282
June12037368
July5352463
August4164488
September6962443
October13652382
November27713204
December454172

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

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Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00049111 (Twitchell Dam). Public domain.