Alturas climate

Alturas Frost Dates and Growing Season

NOAA 1991-2020 normals for Alturas, 0.3 km from Alturas, elevation 4378 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Alturas. 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 June 3 and the first fall freeze around September 13, a growing season of about 97 days.

Median at 32°F
last June 3, first September 13
Median at 28°F
last May 14, first September 27

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 26Jun 18Jun 12Jun 7Jun 3May 31May 27May 22May 15
28°FJun 5May 30May 23May 18May 14May 10May 5Apr 30Apr 26
24°FMay 16May 8May 2Apr 29Apr 25Apr 21Apr 17Apr 11Apr 4
20°FApr 29Apr 21Apr 14Apr 9Apr 5Apr 1Mar 27Mar 20Mar 12
16°FApr 11Apr 3Mar 27Mar 20Mar 14Mar 8Mar 2Feb 25Feb 16

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 27Sep 3Sep 6Sep 10Sep 13Sep 16Sep 19Sep 23Sep 28
28°FSep 11Sep 17Sep 21Sep 24Sep 27Sep 30Oct 3Oct 7Oct 16
24°FSep 27Oct 1Oct 4Oct 8Oct 13Oct 17Oct 22Oct 27Nov 1
20°FOct 9Oct 16Oct 21Oct 26Oct 30Nov 1Nov 4Nov 8Nov 16
16°FOct 21Oct 28Nov 1Nov 4Nov 8Nov 12Nov 16Nov 23Dec 1

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°F918174676257504435
32°F1251141081039792867969
28°F160151145139134129124117105
24°F194187181176170165160153144
20°F236225217210204199193186178
16°F275263254247241234226217205

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
6,300
Cooling degree days, base 65°F
259
Growing degree days, base 40°F
3,977
Growing degree days, base 45°F
2,848
Growing degree days, base 50°F
1,936
Growing degree days, base 55°F
1,211
Growing degree days, base 60°F
647

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,00100
February83400
March76902
April599026
May3604150
June16030325
July32125558
August4384505
September18017295
October501070
November79704
December1,02300

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 0.3 km from Alturas. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00040161 (Alturas). Public domain.