Bemidji climate

Bemidji Frost Dates and Growing Season

NOAA 1991-2020 normals for Cass Lake, 22.3 km from Bemidji, elevation 1296 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Cass Lake. 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 17 and the first fall freeze around September 26, a growing season of about 131 days.

Median at 36°F
last May 28, first September 17
Median at 32°F
last May 17, first September 26
Median at 28°F
last May 7, first October 6

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°FJun 9Jun 4Jun 1May 30May 28May 25May 22May 19May 15
32°FMay 30May 25May 22May 19May 17May 14May 11May 8May 3
28°FMay 20May 17May 13May 10May 7May 4May 1Apr 29Apr 25
24°FMay 12May 7May 3Apr 30Apr 28Apr 26Apr 23Apr 19Apr 14
20°FApr 30Apr 26Apr 23Apr 20Apr 17Apr 14Apr 11Apr 7Apr 3
16°FApr 21Apr 17Apr 14Apr 11Apr 8Apr 6Apr 3Mar 31Mar 26

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 1Sep 7Sep 10Sep 14Sep 17Sep 19Sep 22Sep 25Sep 29
32°FSep 12Sep 17Sep 20Sep 23Sep 26Sep 29Oct 2Oct 5Oct 11
28°FSep 22Sep 27Sep 30Oct 3Oct 6Oct 10Oct 14Oct 17Oct 23
24°FOct 3Oct 7Oct 12Oct 16Oct 20Oct 23Oct 27Oct 30Nov 4
20°FOct 15Oct 21Oct 25Oct 28Nov 1Nov 2Nov 4Nov 8Nov 13
16°FOct 25Oct 30Nov 1Nov 4Nov 6Nov 9Nov 11Nov 15Nov 19

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°F1281221171131101071029790
32°F149143137134131127123118112
28°F170165159155151147143138132
24°F193186181176173168164159152
20°F213207202198193190186180172
16°F228222217214210207203198191

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
9,456
Cooling degree days, base 65°F
375
Growing degree days, base 40°F
3,724
Growing degree days, base 45°F
2,820
Growing degree days, base 50°F
2,027
Growing degree days, base 55°F
1,344
Growing degree days, base 60°F
787

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,79500
February1,49500
March1,21702
April752027
May36816184
June10473422
July37147575
August60109515
September25529255
October683146
November1,11802
December1,57300

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 22.3 km from Bemidji. 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 USC00211374 (Cass Lake). Public domain.