Sun Valley climate

Sun Valley Frost Dates and Growing Season

NOAA 1991-2020 normals for Reno WFO, 3.5 km from Sun Valley, elevation 4987 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Reno WFO. 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 28 and the first fall freeze around October 27, a growing season of about 182 days.

Median at 36°F
last May 14, first October 15
Median at 32°F
last April 28, first October 27
Median at 28°F
last April 10, first November 8

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 5May 31May 25May 19May 14May 10May 6May 1Apr 25
32°FMay 19May 11May 6May 1Apr 28Apr 24Apr 20Apr 16Apr 9
28°FMay 2Apr 25Apr 19Apr 15Apr 10Apr 6Apr 2Mar 27Mar 18
24°FApr 14Apr 6Mar 31Mar 26Mar 19Mar 13Mar 7Feb 28Feb 19
20°FMar 21Mar 11Mar 4Feb 28Feb 23Feb 17Feb 11Feb 2Jan 20
16°FFeb 28Feb 20Feb 13Feb 4Jan 30Jan 21Jan 10Jan 2Dec 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 28Oct 3Oct 7Oct 11Oct 15Oct 18Oct 22Oct 26Nov 1
32°FOct 10Oct 16Oct 21Oct 24Oct 27Oct 31Nov 3Nov 6Nov 10
28°FOct 23Oct 28Nov 1Nov 4Nov 8Nov 10Nov 13Nov 17Nov 23
24°FNov 1Nov 8Nov 12Nov 15Nov 19Nov 23Nov 26Dec 1Dec 7
20°FNov 13Nov 19Nov 24Nov 28Dec 1Dec 5Dec 10Dec 16Dec 25
16°FNov 23Nov 30Dec 5Dec 10Dec 16Dec 21Dec 26Jan 1Jan 17

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°F178169163158152148142134125
32°F208197191186182177171164154
28°F241228221215210204198191181
24°F278267258251245238232224212
20°F320307299291285277270262250
16°F362351341333324317308299285

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
93% 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
4,870
Cooling degree days, base 65°F
1,054
Growing degree days, base 40°F
5,822
Growing degree days, base 45°F
4,504
Growing degree days, base 50°F
3,395
Growing degree days, base 55°F
2,461
Growing degree days, base 60°F
1,687

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January88002
February71005
March611039
April4501103
May22941301
June61155547
July2373837
August4326787
September64141530
October31416212
November642031
December90502

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 3.5 km from Sun Valley. 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 USC00266791 (Reno WFO). Public domain.