Big Delta climate

Big Delta Frost Dates and Growing Season

NOAA 1991-2020 normals for Whitestone Farms, 2.3 km from Big Delta, elevation 995 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Whitestone Farms. 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 26 and the first fall freeze around September 2, a growing season of about 98 days.

Median at 32°F
last May 26, first September 2
Median at 28°F
last May 15, first September 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°F–––––––––
32°FJun 9Jun 3May 31May 29May 26May 24May 21May 18May 14
28°FMay 28May 23May 19May 17May 15May 13May 10May 7May 3
24°FMay 17May 13May 10May 7May 5May 3Apr 30Apr 27Apr 22
20°FMay 8May 4May 1Apr 29Apr 26Apr 23Apr 20Apr 16Apr 13
16°FMay 1Apr 26Apr 23Apr 20Apr 17Apr 14Apr 12Apr 10Apr 6

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°F–––––––––
32°FAug 19Aug 24Aug 28Sep 1Sep 2Sep 5Sep 9Sep 13Sep 18
28°FSep 1Sep 3Sep 8Sep 12Sep 16Sep 20Sep 22Sep 25Sep 29
24°FSep 12Sep 17Sep 20Sep 23Sep 25Sep 28Oct 1Oct 4Oct 8
20°FSep 19Sep 25Sep 28Oct 1Oct 2Oct 5Oct 7Oct 11Oct 16
16°FSep 28Oct 1Oct 4Oct 7Oct 9Oct 11Oct 15Oct 18Oct 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°F928580767267615546
32°F1181111061039895918779
28°F141135131127123120115110102
24°F162156151147143140136131125
20°F177172167163159156152148141
16°F190185180177173169166161155

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
12,900
Cooling degree days, base 65°F
31
Growing degree days, base 40°F
2,236
Growing degree days, base 45°F
1,501
Growing degree days, base 50°F
893
Growing degree days, base 55°F
433
Growing degree days, base 60°F
152

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January2,09100
February1,65400
March1,57300
April91502
May510061
June19812268
July12918354
August3011179
September599027
October1,20401
November1,73800
December1,98900

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 2.3 km from Big 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 USC00509793 (Whitestone Farms). Public domain.