Brown County climate

Brown County Frost Dates and Growing Season

NOAA 1991-2020 normals for Ainsworth, 14.9 km from Brown County, elevation 2510 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Ainsworth. 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 2 and the first fall freeze around October 8, a growing season of about 158 days.

Median at 36°F
last May 12, first September 30
Median at 32°F
last May 2, first October 8
Median at 28°F
last April 22, first October 18

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 25May 20May 17May 15May 12May 10May 6May 4Apr 30
32°FMay 14May 10May 7May 4May 2Apr 30Apr 27Apr 23Apr 19
28°FMay 5May 1Apr 28Apr 25Apr 22Apr 20Apr 17Apr 13Apr 8
24°FApr 25Apr 21Apr 18Apr 14Apr 11Apr 7Apr 4Apr 1Mar 25
20°FApr 19Apr 13Apr 9Apr 5Apr 1Mar 30Mar 26Mar 20Mar 13
16°FApr 10Apr 3Mar 31Mar 27Mar 23Mar 19Mar 15Mar 10Mar 4

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 18Sep 22Sep 25Sep 28Sep 30Oct 2Oct 5Oct 8Oct 12
32°FSep 25Sep 30Oct 2Oct 5Oct 8Oct 11Oct 14Oct 17Oct 21
28°FOct 3Oct 8Oct 13Oct 15Oct 18Oct 21Oct 23Oct 26Oct 30
24°FOct 14Oct 18Oct 21Oct 24Oct 27Oct 29Nov 1Nov 4Nov 9
20°FOct 22Oct 26Oct 30Nov 1Nov 4Nov 7Nov 10Nov 14Nov 20
16°FOct 30Nov 2Nov 6Nov 9Nov 12Nov 15Nov 19Nov 23Nov 28

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°F157151147143139136132128121
32°F177171166162158154150146139
28°F197190186182178174169164158
24°F218211206201197193188183177
20°F238231226221217212208202195
16°F257248242237233228223216210

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
6,275
Cooling degree days, base 65°F
923
Growing degree days, base 40°F
5,363
Growing degree days, base 45°F
4,202
Growing degree days, base 50°F
3,181
Growing degree days, base 55°F
2,295
Growing degree days, base 60°F
1,541

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,20701
February1,01204
March810032
April504499
May22542307
June37166580
July4325786
August10266721
September101108464
October42211161
November801027
December1,14201

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 14.9 km from Brown County. 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 USC00250050 (Ainsworth). Public domain.