Thief River Falls climate

Thief River Falls Frost Dates and Growing Season

NOAA 1991-2020 normals for Thief Rvr Falls 2, 1.5 km from Thief River Falls, elevation 1128 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Thief Rvr Falls 2. 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 28, a growing season of about 135 days.

Median at 36°F
last May 24, first September 18
Median at 32°F
last May 14, first September 28
Median at 28°F
last May 5, first October 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.

Threshold10%20%30%40%50%60%70%80%90%
36°FJun 7Jun 2May 31May 27May 24May 22May 19May 16May 12
32°FMay 29May 24May 21May 17May 14May 12May 9May 6May 2
28°FMay 20May 14May 10May 8May 5May 2Apr 30Apr 26Apr 21
24°FMay 9May 4May 1Apr 28Apr 24Apr 22Apr 18Apr 14Apr 9
20°FApr 30Apr 23Apr 20Apr 17Apr 14Apr 11Apr 9Apr 5Apr 2
16°FApr 20Apr 14Apr 11Apr 8Apr 5Apr 4Apr 1Mar 29Mar 23

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 3Sep 8Sep 12Sep 15Sep 18Sep 20Sep 23Sep 25Sep 30
32°FSep 14Sep 20Sep 22Sep 25Sep 28Sep 30Oct 3Oct 6Oct 11
28°FSep 24Sep 28Oct 1Oct 4Oct 8Oct 11Oct 14Oct 19Oct 25
24°FOct 1Oct 7Oct 11Oct 16Oct 19Oct 23Oct 27Oct 31Nov 4
20°FOct 11Oct 18Oct 23Oct 27Oct 31Nov 1Nov 5Nov 8Nov 12
16°FOct 22Oct 28Nov 1Nov 3Nov 5Nov 8Nov 11Nov 14Nov 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°F13312612211711311010510092
32°F155148143139135131126122114
28°F177169164159155151146141133
24°F199192187181176171166160153
20°F216210206202198193188181174
16°F233226221216212209205201192

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
9,473
Cooling degree days, base 65°F
382
Growing degree days, base 40°F
3,852
Growing degree days, base 45°F
2,927
Growing degree days, base 50°F
2,107
Growing degree days, base 55°F
1,398
Growing degree days, base 60°F
815

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,85000
February1,51100
March1,23101
April701139
May32920213
June8876439
July33132564
August51119533
September24432263
October660353
November1,14602
December1,63000

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 1.5 km from Thief River Falls. 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 USC00218247 (Thief Rvr Falls 2). Public domain.