Deer Lodge Frost Dates and Growing Season

NOAA 1991-2020 normals for Deer Lodge 3 W, 5.2 km from Deer Lodge, elevation 4850 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Deer Lodge 3 W. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

NOAA does not state freeze dates for this station.

Median at 28°F: last May 30, first September 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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	–	–	–	–	–	–	–	–	–
32°F	–	–	–	–	–	–	–	–	–
28°F	Jun 20	Jun 12	Jun 6	Jun 2	May 30	May 25	May 21	May 16	May 11
24°F	May 27	May 20	May 16	May 13	May 10	May 7	May 4	May 1	Apr 28
20°F	May 13	May 9	May 6	May 3	Apr 30	Apr 28	Apr 25	Apr 21	Apr 14
16°F	May 5	Apr 30	Apr 25	Apr 20	Apr 16	Apr 11	Apr 7	Apr 3	Mar 28

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	–	–	–	–	–	–	–	–	–
28°F	Aug 15	Aug 25	Aug 31	Sep 4	Sep 8	Sep 10	Sep 14	Sep 17	Sep 24
24°F	Aug 30	Sep 7	Sep 12	Sep 17	Sep 21	Sep 24	Sep 29	Oct 2	Oct 7
20°F	Sep 16	Sep 23	Sep 26	Sep 30	Oct 3	Oct 5	Oct 9	Oct 13	Oct 19
16°F	Sep 28	Oct 2	Oct 6	Oct 11	Oct 15	Oct 19	Oct 22	Oct 27	Nov 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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	59	50	45	40	36	32	29	26	21
32°F	90	82	77	70	65	60	54	47	39
28°F	124	116	111	105	99	93	87	80	69
24°F	155	147	141	137	132	127	122	114	105
20°F	178	170	165	159	155	151	147	141	134
16°F	205	197	192	187	181	176	171	165	156

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: 9,032
Cooling degree days, base 65°F: 65
Growing degree days, base 40°F: 2,628
Growing degree days, base 45°F: 1,769
Growing degree days, base 50°F: 1,082
Growing degree days, base 55°F: 576
Growing degree days, base 60°F: 242

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	1,335	0	0
February	1,133	0	0
March	1,029	0	0
April	769	0	8
May	529	1	61
June	330	4	157
July	138	34	364
August	155	25	342
September	389	2	130
October	756	0	21
November	1,103	0	1
December	1,367	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 5.2 km from Deer Lodge. 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 USC00242275 (Deer Lodge 3 W). Public domain.