Bismarck climate

Bismarck Frost Dates and Growing Season

NOAA 1991-2020 normals for Bismarck, 4.5 km from Bismarck, elevation 1658 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Bismarck. 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 14 and the first fall freeze around September 27, a growing season of about 136 days.

Median at 36°F
last May 25, first September 19
Median at 32°F
last May 14, first September 27
Median at 28°F
last May 3, first October 5

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 7Jun 2May 30May 27May 25May 22May 18May 15May 11
32°FMay 27May 22May 19May 16May 14May 11May 8May 5May 1
28°FMay 17May 13May 10May 6May 3May 1Apr 29Apr 26Apr 20
24°FMay 8May 4May 1Apr 28Apr 25Apr 21Apr 18Apr 14Apr 10
20°FApr 30Apr 25Apr 20Apr 17Apr 14Apr 11Apr 8Apr 5Apr 1
16°FApr 20Apr 14Apr 10Apr 8Apr 5Apr 2Mar 31Mar 27Mar 19

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 7Sep 11Sep 14Sep 17Sep 19Sep 21Sep 23Sep 26Sep 29
32°FSep 15Sep 20Sep 23Sep 25Sep 27Sep 29Oct 2Oct 5Oct 9
28°FSep 22Sep 27Sep 30Oct 3Oct 5Oct 8Oct 10Oct 13Oct 18
24°FOct 1Oct 5Oct 8Oct 12Oct 14Oct 17Oct 20Oct 23Oct 27
20°FOct 9Oct 14Oct 19Oct 21Oct 24Oct 27Oct 29Nov 1Nov 5
16°FOct 20Oct 24Oct 28Oct 31Nov 2Nov 4Nov 7Nov 10Nov 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.

Threshold10%20%30%40%50%60%70%80%90%
36°F13312812311911611210810396
32°F153147143139136132128124117
28°F174167162158154150146142135
24°F192187182177173169164160153
20°F212206201196192187183178171
16°F230224219214210206202197190

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
8,471
Cooling degree days, base 65°F
536
Growing degree days, base 40°F
4,180
Growing degree days, base 45°F
3,208
Growing degree days, base 50°F
2,355
Growing degree days, base 55°F
1,621
Growing degree days, base 60°F
1,010

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,61800
February1,33000
March1,08404
April655140
May31617212
June7789463
July16211660
August31174608
September20444308
October626258
November1,05502
December1,46000

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

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Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USW00024011 (Bismarck). Public domain.