Delta County climate

Delta County Frost Dates and Growing Season

NOAA 1991-2020 normals for Cooper Dam, 9.8 km from Delta County, elevation 463 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Cooper 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 March 18 and the first fall freeze around November 13, a growing season of about 241 days.

Median at 36°F
last March 30, first November 4
Median at 32°F
last March 18, first November 13
Median at 28°F
last March 6, first November 26

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 16Apr 8Apr 4Apr 1Mar 30Mar 27Mar 23Mar 19Mar 14
32°FApr 1Mar 28Mar 24Mar 21Mar 18Mar 14Mar 11Mar 6Mar 1
28°FMar 23Mar 18Mar 14Mar 10Mar 6Mar 3Feb 28Feb 23Feb 13
24°FMar 14Mar 8Mar 4Feb 28Feb 23Feb 15Feb 7Jan 31Jan 22
20°FMar 7Feb 28Feb 20Feb 10Feb 2Jan 29Jan 22Jan 13Dec 31
16°FFeb 28Feb 14Feb 5Jan 30Jan 25Jan 20Jan 13Jan 4Dec 25

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 22Oct 27Oct 31Nov 2Nov 4Nov 6Nov 10Nov 14Nov 20
32°FOct 30Nov 3Nov 6Nov 9Nov 13Nov 17Nov 21Nov 27Dec 1
28°FNov 6Nov 11Nov 17Nov 21Nov 26Dec 1Dec 4Dec 9Dec 20
24°FNov 17Nov 26Dec 1Dec 6Dec 12Dec 21Dec 27Jan 1Jan 9
20°FDec 3Dec 11Dec 19Dec 25Jan 1Jan 4Jan 10Jan 17Feb 1
16°FDec 14Dec 22Dec 30Jan 3Jan 8Jan 14Jan 20Jan 29Feb 9

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°F242234229224220215210205197
32°F266257251246241236232227218
28°F300287279271266260253247239
24°F334322311304298290282272261
20°F365355344335329321311302292
16°F365365365365360350342331314

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
99% of years
20°F or colder
90% of years
16°F or colder
57% 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
2,559
Cooling degree days, base 65°F
2,425
Growing degree days, base 40°F
9,152
Growing degree days, base 45°F
7,517
Growing degree days, base 50°F
6,015
Growing degree days, base 55°F
4,660
Growing degree days, base 60°F
3,461

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January652149
February474596
March32021223
April11774414
May19233679
June0447897
July05811,046
August05671,032
September3351798
October92126503
November31517201
December567378

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 9.8 km from Delta County. 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 USC00411968 (Cooper Dam). Public domain.