Rock Island climate

Rock Island Frost Dates and Growing Season

NOAA 1991-2020 normals for Wenatchee Pangborn AP, 4.9 km from Rock Island, elevation 1229 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Wenatchee Pangborn AP. 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 April 8 and the first fall freeze around October 24, a growing season of about 200 days.

Median at 36°F
last April 25, first October 14
Median at 32°F
last April 8, first October 24
Median at 28°F
last March 17, first November 4

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 8May 3Apr 30Apr 27Apr 25Apr 23Apr 20Apr 16Apr 11
32°FApr 23Apr 17Apr 14Apr 10Apr 8Apr 4Apr 1Mar 28Mar 20
28°FApr 6Apr 1Mar 27Mar 22Mar 17Mar 13Mar 9Mar 6Mar 2
24°FMar 19Mar 13Mar 8Mar 5Mar 2Feb 28Feb 23Feb 18Feb 11
20°FMar 8Mar 1Feb 26Feb 21Feb 17Feb 13Feb 7Feb 2Jan 25
16°FFeb 26Feb 20Feb 13Feb 8Feb 3Jan 29Jan 22Jan 15Jan 4

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 3Oct 7Oct 10Oct 12Oct 14Oct 16Oct 19Oct 21Oct 25
32°FOct 12Oct 16Oct 19Oct 22Oct 24Oct 26Oct 29Nov 1Nov 5
28°FOct 20Oct 25Oct 29Nov 1Nov 4Nov 6Nov 9Nov 13Nov 18
24°FOct 29Nov 3Nov 8Nov 12Nov 15Nov 18Nov 23Nov 27Dec 4
20°FNov 10Nov 15Nov 20Nov 24Nov 28Dec 3Dec 7Dec 13Dec 24
16°FNov 21Nov 28Dec 2Dec 6Dec 11Dec 17Dec 23Dec 30Jan 10

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°F189182178174171168164160153
32°F219213208203200195191185179
28°F253244240235230225221216208
24°F285273266261256252247241233
20°F318305297289282276270263255
16°F347334328320313306299290277

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
97% 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
5,813
Cooling degree days, base 65°F
807
Growing degree days, base 40°F
5,169
Growing degree days, base 45°F
3,984
Growing degree days, base 50°F
2,962
Growing degree days, base 55°F
2,096
Growing degree days, base 60°F
1,374

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,12100
February85400
March679012
April418291
May18636319
June59105497
July6306766
August7277735
September9179439
October4463102
November83002
December1,11800

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 4.9 km from Rock Island. 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 USW00094239 (Wenatchee Pangborn AP). Public domain.