International Falls climate

International Falls Frost Dates and Growing Season

NOAA 1991-2020 normals for Intl Falls Intl AP, 4.5 km from International Falls, elevation 1183 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Intl Falls Intl 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 29 and the first fall freeze around September 13, a growing season of about 109 days.

Median at 32°F
last May 29, first September 13
Median at 28°F
last May 14, first September 26

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 16Jun 8Jun 4Jun 1May 29May 26May 22May 18May 13
28°FMay 30May 25May 21May 17May 14May 10May 7May 4Apr 30
24°FMay 19May 13May 8May 5May 2Apr 30Apr 28Apr 25Apr 20
20°FMay 8May 2Apr 29Apr 26Apr 23Apr 20Apr 18Apr 14Apr 9
16°FApr 27Apr 22Apr 18Apr 16Apr 13Apr 10Apr 7Apr 4Mar 31

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

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°F1029387827670635647
32°F128122117113109105999487
28°F154147142137133128124118111
24°F177169164159155150146139132
20°F200192187183178173169163154
16°F220213209205200196193187179

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
10,181
Cooling degree days, base 65°F
174
Growing degree days, base 40°F
3,135
Growing degree days, base 45°F
2,279
Growing degree days, base 50°F
1,543
Growing degree days, base 55°F
930
Growing degree days, base 60°F
465

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,86100
February1,55300
March1,28402
April807014
May4378130
June16035331
July7570460
August11549400
September33612176
October740128
November1,16302
December1,65100

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 International Falls. 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 USW00014918 (Intl Falls Intl AP). Public domain.