Delta climate

Delta Frost Dates and Growing Season

NOAA 1991-2020 normals for Delta, 1.8 km from Delta, elevation 4620 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Delta. 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 16 and the first fall freeze around September 29, a growing season of about 137 days.

Median at 36°F
last May 29, first September 22
Median at 32°F
last May 16, first September 29
Median at 28°F
last May 2, first October 9

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 16Jun 9Jun 4Jun 1May 29May 26May 23May 18May 12
32°FJun 5May 28May 23May 19May 16May 11May 8May 4Apr 29
28°FMay 19May 13May 9May 5May 2Apr 30Apr 26Apr 22Apr 17
24°FMay 6May 1Apr 27Apr 24Apr 20Apr 16Apr 13Apr 9Apr 1
20°FApr 24Apr 16Apr 11Apr 6Apr 2Mar 29Mar 25Mar 18Mar 10
16°FApr 5Mar 30Mar 24Mar 17Mar 12Mar 8Mar 5Mar 1Feb 23

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 8Sep 13Sep 17Sep 19Sep 22Sep 24Sep 26Sep 29Oct 2
32°FSep 16Sep 21Sep 24Sep 27Sep 29Oct 1Oct 4Oct 7Oct 11
28°FSep 27Oct 1Oct 3Oct 6Oct 9Oct 12Oct 15Oct 18Oct 23
24°FOct 6Oct 10Oct 13Oct 16Oct 18Oct 21Oct 25Oct 29Nov 3
20°FOct 15Oct 19Oct 23Oct 26Oct 29Nov 1Nov 4Nov 8Nov 12
16°FOct 24Oct 29Nov 1Nov 5Nov 8Nov 11Nov 15Nov 18Nov 22

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°F13412712311811411010510093
32°F155150145141137133128122113
28°F181173168163160155151145136
24°F204196191187182177172166159
20°F235226220215208203197192183
16°F263256249243238233228222210

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
6,093
Cooling degree days, base 65°F
882
Growing degree days, base 40°F
5,173
Growing degree days, base 45°F
4,010
Growing degree days, base 50°F
3,015
Growing degree days, base 55°F
2,169
Growing degree days, base 60°F
1,463

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,16600
February88101
March696019
April488175
May23424273
June54144541
July2351813
August4291752
September10370423
October4543111
November83708
December1,17500

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 1.8 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 USW00023162 (Delta). Public domain.