Arnold climate

Arnold Frost Dates and Growing Season

NOAA 1991-2020 normals for Arnold 4 Wnw, 6.7 km from Arnold, elevation 2877 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Arnold 4 Wnw. 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 5 and the first fall freeze around October 3, a growing season of about 149 days.

Median at 36°F
last May 14, first September 25
Median at 32°F
last May 5, first October 3
Median at 28°F
last April 26, first October 13

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 27May 23May 20May 17May 14May 12May 10May 6May 2
32°FMay 19May 14May 11May 8May 5May 3May 1Apr 28Apr 23
28°FMay 8May 4May 2Apr 29Apr 26Apr 23Apr 21Apr 18Apr 13
24°FMay 1Apr 26Apr 22Apr 19Apr 16Apr 13Apr 9Apr 6Apr 1
20°FApr 20Apr 15Apr 11Apr 7Apr 4Apr 1Mar 29Mar 24Mar 18
16°FApr 11Apr 4Mar 31Mar 28Mar 24Mar 20Mar 16Mar 12Mar 7

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 13Sep 17Sep 20Sep 22Sep 25Sep 27Sep 30Oct 2Oct 6
32°FSep 21Sep 26Sep 29Oct 1Oct 3Oct 6Oct 8Oct 11Oct 15
28°FSep 30Oct 4Oct 7Oct 10Oct 13Oct 15Oct 18Oct 21Oct 26
24°FOct 9Oct 14Oct 17Oct 20Oct 22Oct 25Oct 28Oct 31Nov 3
20°FOct 18Oct 22Oct 26Oct 28Oct 31Nov 2Nov 5Nov 8Nov 12
16°FOct 26Oct 31Nov 2Nov 5Nov 8Nov 11Nov 13Nov 17Nov 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°F149144139135132129125120115
32°F167161156153149146142137131
28°F187180176173169165161156149
24°F207202197193188185180176168
20°F229223217212208204200195189
16°F247241236231227223218212205

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
6,881
Cooling degree days, base 65°F
686
Growing degree days, base 40°F
4,740
Growing degree days, base 45°F
3,655
Growing degree days, base 50°F
2,714
Growing degree days, base 55°F
1,905
Growing degree days, base 60°F
1,232

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,26800
February1,06501
March867014
April563164
May27926248
June47134538
July5267727
August20193639
September14760372
October5164103
November888010
December1,21700

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 6.7 km from Arnold. 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 USC00250355 (Arnold 4 Wnw). Public domain.