Monona County climate

Monona County Frost Dates and Growing Season

NOAA 1991-2020 normals for Castana Exp Farm, 10.3 km from Monona County, elevation 1400 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Castana Exp Farm. 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 25 and the first fall freeze around October 12, a growing season of about 170 days.

Median at 36°F
last May 4, first October 3
Median at 32°F
last April 25, first October 12
Median at 28°F
last April 15, first October 23

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 15May 11May 8May 6May 4May 2Apr 30Apr 27Apr 23
32°FMay 7May 2Apr 30Apr 28Apr 25Apr 22Apr 19Apr 15Apr 11
28°FApr 28Apr 23Apr 20Apr 18Apr 15Apr 12Apr 9Apr 5Apr 1
24°FApr 20Apr 16Apr 12Apr 9Apr 6Apr 3Mar 31Mar 28Mar 20
20°FApr 13Apr 7Apr 4Apr 1Mar 30Mar 26Mar 22Mar 17Mar 12
16°FApr 6Apr 1Mar 28Mar 24Mar 20Mar 17Mar 13Mar 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 21Sep 25Sep 28Oct 1Oct 3Oct 6Oct 9Oct 13Oct 17
32°FSep 28Oct 2Oct 6Oct 9Oct 12Oct 16Oct 18Oct 22Oct 27
28°FOct 7Oct 14Oct 18Oct 20Oct 23Oct 26Oct 29Nov 1Nov 4
24°FOct 19Oct 23Oct 27Oct 30Nov 1Nov 3Nov 6Nov 10Nov 14
20°FOct 25Oct 31Nov 2Nov 5Nov 8Nov 11Nov 14Nov 18Nov 23
16°FNov 1Nov 6Nov 9Nov 12Nov 15Nov 18Nov 22Nov 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°F169163158155151148144140134
32°F188182177173170166161157151
28°F208202197193189185180176169
24°F227220215211208204200194188
20°F245237232227223219215210202
16°F261254249244240235231225217

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
6,879
Cooling degree days, base 65°F
804
Growing degree days, base 40°F
5,123
Growing degree days, base 45°F
4,024
Growing degree days, base 50°F
3,036
Growing degree days, base 55°F
2,163
Growing degree days, base 60°F
1,417

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,41200
February1,15202
March895126
April509597
May20348329
June26174598
July4274735
August12209662
September11583424
October44011147
November858017
December1,25401

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 10.3 km from Monona 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 USC00131277 (Castana Exp Farm). Public domain.