Delta climate

Delta Frost Dates and Growing Season

NOAA 1991-2020 normals for Delta 3E, 3.8 km from Delta, elevation 5027 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Delta 3E. 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 1 and the first fall freeze around October 7, a growing season of about 159 days.

Median at 36°F
last May 14, first September 30
Median at 32°F
last May 1, first October 7
Median at 28°F
last April 19, first October 16

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°FMay 29May 23May 19May 17May 14May 11May 8May 4May 1
32°FMay 14May 9May 5May 3May 1Apr 29Apr 26Apr 22Apr 19
28°FMay 3Apr 29Apr 25Apr 21Apr 19Apr 16Apr 13Apr 9Apr 5
24°FApr 20Apr 14Apr 10Apr 7Apr 3Apr 1Mar 29Mar 24Mar 19
20°FApr 3Mar 29Mar 24Mar 21Mar 17Mar 14Mar 11Mar 6Mar 2
16°FMar 20Mar 14Mar 9Mar 5Mar 3Feb 28Feb 24Feb 18Feb 11

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°FSep 20Sep 23Sep 26Sep 27Sep 30Oct 1Oct 3Oct 6Oct 9
32°FSep 26Sep 30Oct 3Oct 5Oct 7Oct 9Oct 12Oct 16Oct 19
28°FOct 3Oct 7Oct 11Oct 14Oct 16Oct 18Oct 21Oct 24Oct 29
24°FOct 13Oct 17Oct 21Oct 24Oct 27Oct 29Nov 1Nov 5Nov 9
20°FOct 22Oct 27Oct 31Nov 3Nov 5Nov 8Nov 12Nov 15Nov 20
16°FOct 30Nov 5Nov 9Nov 13Nov 16Nov 18Nov 22Nov 25Nov 30

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°F155149145142138135131126119
32°F175169166162159155152148142
28°F199192187184180176172168161
24°F227218214209205202197192184
20°F255247242238233228223218211
16°F279270265260256252247240232

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
5,802
Cooling degree days, base 65°F
833
Growing degree days, base 40°F
5,298
Growing degree days, base 45°F
4,115
Growing degree days, base 50°F
3,082
Growing degree days, base 55°F
2,194
Growing degree days, base 60°F
1,446

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,17000
February85501
March673022
April4241104
May18631322
June32174593
July0321786
August2239702
September8564432
October4282115
November79707
December1,15000

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 3.8 km from Delta. 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 USC00052196 (Delta 3E). Public domain.