Cascade climate

Cascade Frost Dates and Growing Season

NOAA 1991-2020 normals for Cascade 1 Nw, 0.9 km from Cascade, elevation 4896 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Cascade 1 Nw. 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 30 and the first fall freeze around September 19, a growing season of about 110 days.

Median at 32°F
last May 30, first September 19
Median at 28°F
last May 6, first October 2

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 21Jun 14Jun 8Jun 3May 30May 24May 19May 15May 10
28°FMay 28May 18May 13May 10May 6May 3May 1Apr 27Apr 21
24°FMay 6Apr 30Apr 27Apr 23Apr 19Apr 16Apr 12Apr 9Apr 4
20°FApr 21Apr 14Apr 10Apr 7Apr 4Apr 1Mar 29Mar 23Mar 18
16°FApr 10Apr 4Mar 31Mar 27Mar 23Mar 19Mar 15Mar 11Mar 5

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°FSep 3Sep 7Sep 12Sep 15Sep 19Sep 24Sep 27Oct 1Oct 4
28°FSep 15Sep 22Sep 27Sep 30Oct 2Oct 5Oct 9Oct 13Oct 18
24°FSep 30Oct 4Oct 8Oct 12Oct 16Oct 20Oct 23Oct 28Nov 3
20°FOct 13Oct 19Oct 23Oct 26Oct 30Nov 2Nov 6Nov 11Nov 18
16°FOct 25Oct 30Nov 3Nov 8Nov 12Nov 16Nov 20Nov 23Nov 28

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°F999085817672676253
32°F136128122115110105989181
28°F170162157152147142136129120
24°F201192188183178173168161154
20°F231225219213208204199192182
16°F258249243237233227222216207

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
8,040
Cooling degree days, base 65°F
160
Growing degree days, base 40°F
3,168
Growing degree days, base 45°F
2,240
Growing degree days, base 50°F
1,489
Growing degree days, base 55°F
888
Growing degree days, base 60°F
443

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,29600
February1,05700
March95200
April713010
May466192
June26313223
July7380474
August8060446
September2756209
October633035
November95700
December1,27700

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 0.9 km from Cascade. 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 USC00101514 (Cascade 1 Nw). Public domain.