Brown County climate

Brown County Frost Dates and Growing Season

NOAA 1991-2020 normals for New Ulm 2 Se, 20 km from Brown County, elevation 890 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for New Ulm 2 Se. 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 29 and the first fall freeze around October 7, a growing season of about 161 days.

Median at 36°F
last May 7, first September 28
Median at 32°F
last April 29, first October 7
Median at 28°F
last April 18, first October 21

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 23May 16May 13May 10May 7May 5May 3Apr 30Apr 25
32°FMay 12May 7May 4May 1Apr 29Apr 26Apr 23Apr 19Apr 15
28°FMay 2Apr 27Apr 24Apr 20Apr 18Apr 15Apr 11Apr 7Apr 3
24°FApr 23Apr 18Apr 15Apr 11Apr 8Apr 6Apr 3Mar 31Mar 26
20°FApr 17Apr 10Apr 6Apr 3Mar 31Mar 29Mar 24Mar 20Mar 15
16°FApr 7Apr 2Mar 29Mar 26Mar 22Mar 19Mar 16Mar 12Mar 7

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 16Sep 19Sep 23Sep 26Sep 28Oct 1Oct 4Oct 7Oct 12
32°FSep 22Sep 28Oct 1Oct 5Oct 7Oct 11Oct 15Oct 19Oct 23
28°FOct 4Oct 9Oct 13Oct 18Oct 21Oct 23Oct 26Oct 28Nov 1
24°FOct 14Oct 21Oct 24Oct 27Oct 30Nov 1Nov 4Nov 8Nov 13
20°FOct 24Oct 30Nov 1Nov 4Nov 7Nov 9Nov 12Nov 16Nov 22
16°FNov 1Nov 5Nov 8Nov 11Nov 13Nov 16Nov 20Nov 25Dec 1

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°F161156151147143139135130124
32°F180174170165161157153147141
28°F204196191186182179175170162
24°F223215211207203198194189183
20°F241234229224220216211206198
16°F257251245240235231227222214

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
7,585
Cooling degree days, base 65°F
676
Growing degree days, base 40°F
4,746
Growing degree days, base 45°F
3,700
Growing degree days, base 50°F
2,767
Growing degree days, base 55°F
1,945
Growing degree days, base 60°F
1,240

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,54200
February1,26100
March1,00508
April557475
May22839297
June39153564
July9236693
August21167611
September13869389
October4938118
November926013
December1,36700

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 20 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 USC00215887 (New Ulm 2 Se). Public domain.