Ironton climate

Ironton Frost Dates and Growing Season

NOAA 1991-2020 normals for Brainerd Crow Wing CO AP, 14.3 km from Ironton, elevation 1221 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Brainerd Crow Wing CO 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 13 and the first fall freeze around September 27, a growing season of about 138 days.

Median at 36°F
last May 24, first September 19
Median at 32°F
last May 13, first September 27
Median at 28°F
last May 2, 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 6Jun 1May 29May 27May 24May 21May 18May 14May 8
32°FMay 27May 23May 19May 16May 13May 9May 6May 3Apr 29
28°FMay 17May 11May 7May 4May 2Apr 30Apr 26Apr 23Apr 17
24°FMay 6May 1Apr 27Apr 24Apr 21Apr 19Apr 16Apr 12Apr 7
20°FApr 25Apr 21Apr 18Apr 15Apr 11Apr 8Apr 5Apr 3Mar 31
16°FApr 20Apr 13Apr 9Apr 6Apr 4Apr 2Mar 30Mar 25Mar 20

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 4Sep 10Sep 14Sep 16Sep 19Sep 21Sep 24Sep 27Oct 1
32°FSep 14Sep 18Sep 22Sep 25Sep 27Sep 30Oct 3Oct 7Oct 12
28°FSep 22Sep 28Oct 2Oct 5Oct 8Oct 11Oct 14Oct 19Oct 22
24°FOct 4Oct 11Oct 14Oct 19Oct 22Oct 24Oct 28Oct 31Nov 3
20°FOct 19Oct 23Oct 28Oct 31Nov 1Nov 4Nov 6Nov 10Nov 15
16°FOct 30Nov 1Nov 4Nov 6Nov 9Nov 12Nov 15Nov 19Nov 23

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°F13613012612111611210710396
32°F157151146142138134130125117
28°F179172167163158154150145138
24°F202194189185182177173167159
20°F221214210206202198193189181
16°F237231226222218214210205199

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
8,696
Cooling degree days, base 65°F
413
Growing degree days, base 40°F
3,998
Growing degree days, base 45°F
3,036
Growing degree days, base 50°F
2,187
Growing degree days, base 55°F
1,458
Growing degree days, base 60°F
864

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,68500
February1,38700
March1,12705
April676137
May32019204
June7882455
July22165607
August41111535
September22334280
October609260
November1,03403
December1,49400

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 14.3 km from Ironton. 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 USW00094938 (Brainerd Crow Wing CO AP). Public domain.