Anaconda Frost Dates and Growing Season

NOAA 1991-2020 normals for Anaconda, 0.7 km from Anaconda, elevation 5230 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Anaconda. 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 1 and the first fall freeze around September 14, a growing season of about 105 days.

Median at 32°F: last June 1, first September 14
Median at 28°F: last May 13, first September 28

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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	–	–	–	–	–	–	–	–	–
32°F	Jun 25	Jun 17	Jun 11	Jun 5	Jun 1	May 29	May 25	May 20	May 14
28°F	May 30	May 23	May 19	May 16	May 13	May 10	May 6	May 3	Apr 29
24°F	May 13	May 9	May 6	May 3	May 1	Apr 29	Apr 25	Apr 22	Apr 17
20°F	May 4	Apr 30	Apr 27	Apr 23	Apr 20	Apr 16	Apr 12	Apr 8	Apr 2
16°F	Apr 26	Apr 19	Apr 14	Apr 9	Apr 6	Apr 2	Mar 29	Mar 21	Mar 14

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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	–	–	–	–	–	–	–	–	–
32°F	Aug 31	Sep 4	Sep 8	Sep 11	Sep 14	Sep 17	Sep 21	Sep 24	Oct 1
28°F	Sep 12	Sep 17	Sep 22	Sep 25	Sep 28	Oct 1	Oct 3	Oct 6	Oct 12
24°F	Sep 23	Sep 29	Oct 2	Oct 5	Oct 7	Oct 11	Oct 14	Oct 18	Oct 23
20°F	Oct 3	Oct 7	Oct 12	Oct 16	Oct 19	Oct 22	Oct 26	Oct 31	Nov 5
16°F	Oct 12	Oct 18	Oct 24	Oct 28	Oct 31	Nov 2	Nov 6	Nov 10	Nov 15

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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	96	88	82	76	71	66	61	54	46
32°F	129	120	114	109	105	99	94	88	78
28°F	159	152	146	142	138	134	128	123	116
24°F	181	175	169	164	161	157	153	148	142
20°F	207	199	192	188	182	178	174	168	161
16°F	233	225	218	212	207	201	196	189	181

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: 7,879
Cooling degree days, base 65°F: 177
Growing degree days, base 40°F: 3,285
Growing degree days, base 45°F: 2,335
Growing degree days, base 50°F: 1,559
Growing degree days, base 55°F: 940
Growing degree days, base 60°F: 476

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	1,201	0	0
February	1,040	0	0
March	924	0	1
April	704	0	17
May	459	2	105
June	232	15	247
July	65	86	487
August	82	63	448
September	282	11	212
October	657	0	39
November	980	0	2
December	1,254	0	0

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

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00240199 (Anaconda). Public domain.