Marion climate

Marion Frost Dates and Growing Season

NOAA 1991-2020 normals for Kalispell Glacier AP, 36.9 km from Marion, elevation 2957 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Kalispell Glacier AP. 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 31 and the first fall freeze around September 10, a growing season of about 100 days.

Median at 32°F
last May 31, first September 10
Median at 28°F
last May 10, 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 22Jun 14Jun 7Jun 3May 31May 27May 23May 19May 13
28°FMay 26May 20May 16May 13May 10May 8May 5May 2Apr 28
24°FMay 11May 7May 4May 1Apr 28Apr 24Apr 21Apr 16Apr 9
20°FApr 25Apr 18Apr 14Apr 8Apr 3Mar 31Mar 27Mar 21Mar 14
16°FApr 5Mar 30Mar 25Mar 19Mar 15Mar 12Mar 8Mar 5Feb 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.

Threshold10%20%30%40%50%60%70%80%90%
36°F–––––––––
32°FAug 26Aug 31Sep 4Sep 7Sep 10Sep 13Sep 17Sep 21Sep 25
28°FSep 9Sep 17Sep 20Sep 23Sep 27Sep 29Oct 1Oct 3Oct 7
24°FSep 24Sep 29Oct 1Oct 4Oct 6Oct 9Oct 13Oct 16Oct 21
20°FOct 3Oct 8Oct 12Oct 16Oct 19Oct 22Oct 25Oct 30Nov 4
16°FOct 14Oct 20Oct 25Oct 28Nov 1Nov 4Nov 9Nov 15Nov 25

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°F867771666055494235
32°F12311511010510095898270
28°F155149146140136132128122115
24°F186178172167162158154149142
20°F224214208202196191185178171
16°F255246240235229225218212203

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
8,106
Cooling degree days, base 65°F
143
Growing degree days, base 40°F
3,106
Growing degree days, base 45°F
2,185
Growing degree days, base 50°F
1,425
Growing degree days, base 55°F
823
Growing degree days, base 60°F
399

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,28200
February1,07000
March94400
April668013
May4171109
June23412236
July7572462
August9555426
September3244164
October725016
November1,00700
December1,26800

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 36.9 km from Marion. 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 USC00244558 (Kalispell Glacier AP). Public domain.