Arnold climate

Arnold Frost Dates and Growing Season

NOAA 1991-2020 normals for Natrona Lock 4, 5.5 km from Arnold, elevation 760 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Natrona Lock 4. 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 16 and the first fall freeze around November 2, a growing season of about 199 days.

Median at 36°F
last April 29, first October 21
Median at 32°F
last April 16, first November 2
Median at 28°F
last April 3, first November 14

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 16May 10May 5May 2Apr 29Apr 25Apr 22Apr 19Apr 14
32°FMay 2Apr 26Apr 21Apr 18Apr 16Apr 12Apr 9Apr 5Mar 31
28°FApr 16Apr 12Apr 8Apr 5Apr 3Apr 1Mar 29Mar 25Mar 19
24°FApr 6Apr 2Mar 30Mar 28Mar 25Mar 20Mar 18Mar 15Mar 10
20°FMar 29Mar 25Mar 21Mar 18Mar 15Mar 12Mar 8Mar 4Feb 27
16°FMar 21Mar 16Mar 12Mar 9Mar 5Mar 2Feb 26Feb 19Feb 11

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 7Oct 12Oct 15Oct 18Oct 21Oct 23Oct 26Oct 30Nov 3
32°FOct 20Oct 24Oct 28Oct 31Nov 2Nov 5Nov 8Nov 11Nov 16
28°FNov 2Nov 5Nov 9Nov 11Nov 14Nov 16Nov 20Nov 24Dec 1
24°FNov 9Nov 14Nov 18Nov 21Nov 25Nov 28Dec 1Dec 6Dec 12
20°FNov 19Nov 25Nov 30Dec 3Dec 7Dec 10Dec 15Dec 20Dec 27
16°FDec 1Dec 6Dec 11Dec 16Dec 20Dec 24Dec 29Jan 1Jan 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°F194187182178174170165160153
32°F218212207203199195191186178
28°F245237232228224220217213206
24°F268261255250245241236231224
20°F292285278274269264259252243
16°F315306300294289284279274265

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
5,680
Cooling degree days, base 65°F
788
Growing degree days, base 40°F
5,392
Growing degree days, base 45°F
4,195
Growing degree days, base 50°F
3,141
Growing degree days, base 55°F
2,223
Growing degree days, base 60°F
1,436

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,13102
February96604
March828119
April4424120
May17247351
June22150578
July3264725
August5222682
September8192461
October36611168
November683028
December98103

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 5.5 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 USC00366151 (Natrona Lock 4). Public domain.