Brown County climate

Brown County Frost Dates and Growing Season

NOAA 1991-2020 normals for Hiawatha 1 S, 2.9 km from Brown County, elevation 1061 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Hiawatha 1 S. 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 April 14 and the first fall freeze around October 22, a growing season of about 188 days.

Median at 36°F
last April 24, first October 10
Median at 32°F
last April 14, first October 22
Median at 28°F
last April 5, first November 1

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°FMay 7May 3Apr 30Apr 27Apr 24Apr 21Apr 18Apr 15Apr 11
32°FApr 28Apr 23Apr 20Apr 16Apr 14Apr 11Apr 8Apr 5Apr 1
28°FApr 19Apr 14Apr 11Apr 8Apr 5Apr 2Mar 31Mar 27Mar 20
24°FApr 10Apr 4Apr 1Mar 30Mar 27Mar 23Mar 19Mar 14Mar 7
20°FApr 1Mar 28Mar 23Mar 20Mar 16Mar 13Mar 9Mar 5Feb 28
16°FMar 23Mar 18Mar 14Mar 10Mar 6Mar 3Feb 28Feb 25Feb 18

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 25Sep 30Oct 3Oct 7Oct 10Oct 13Oct 16Oct 20Oct 24
32°FOct 5Oct 12Oct 16Oct 20Oct 22Oct 24Oct 27Oct 30Nov 2
28°FOct 18Oct 23Oct 25Oct 29Nov 1Nov 2Nov 5Nov 8Nov 13
24°FOct 28Nov 1Nov 3Nov 6Nov 9Nov 12Nov 15Nov 20Nov 26
20°FNov 4Nov 8Nov 13Nov 16Nov 19Nov 23Nov 27Dec 1Dec 6
16°FNov 12Nov 17Nov 21Nov 25Nov 29Dec 1Dec 5Dec 11Dec 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°F186179174170167162158154147
32°F207201197192188184180175168
28°F230221217212209205200195189
24°F254243237232227222217213206
20°F273264258254248242237232224
16°F291283277271266262257250242

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
5,664
Cooling degree days, base 65°F
1,152
Growing degree days, base 40°F
5,942
Growing degree days, base 45°F
4,723
Growing degree days, base 50°F
3,638
Growing degree days, base 55°F
2,678
Growing degree days, base 60°F
1,848

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,21900
February96507
March748241
April3888155
May13984418
June8246688
July2368831
August5302762
September79122495
October34019207
November704032
December1,06902

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 2.9 km from Brown County. 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 USC00143634 (Hiawatha 1 S). Public domain.