Viola climate

Viola Frost Dates and Growing Season

NOAA 1991-2020 normals for Viroqua, 17.8 km from Viola, elevation 1255 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Viroqua. 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 7 and the first fall freeze around October 2, a growing season of about 148 days.

Median at 36°F
last May 16, first September 25
Median at 32°F
last May 7, first October 2
Median at 28°F
last April 27, first October 13

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 31May 26May 22May 19May 16May 14May 12May 9May 5
32°FMay 21May 17May 13May 10May 7May 4May 1Apr 28Apr 23
28°FMay 11May 6May 3Apr 30Apr 27Apr 23Apr 20Apr 16Apr 11
24°FMay 1Apr 25Apr 22Apr 18Apr 15Apr 12Apr 8Apr 5Apr 1
20°FApr 22Apr 15Apr 11Apr 7Apr 5Apr 2Mar 31Mar 26Mar 20
16°FApr 11Apr 6Apr 3Mar 31Mar 29Mar 25Mar 21Mar 17Mar 11

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 10Sep 15Sep 19Sep 22Sep 25Sep 27Sep 30Oct 3Oct 6
32°FSep 18Sep 23Sep 27Sep 30Oct 2Oct 5Oct 8Oct 11Oct 17
28°FSep 27Oct 2Oct 6Oct 10Oct 13Oct 16Oct 20Oct 23Oct 28
24°FOct 6Oct 13Oct 18Oct 21Oct 24Oct 27Oct 30Nov 2Nov 8
20°FOct 19Oct 26Oct 30Nov 1Nov 4Nov 6Nov 10Nov 13Nov 18
16°FNov 1Nov 4Nov 7Nov 10Nov 13Nov 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°F148141137133129126122117110
32°F166159155151148144140136130
28°F188181176171168163159154147
24°F211204199194191185181176168
20°F232225219215211207203197188
16°F252244239234230226222217210

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
8,132
Cooling degree days, base 65°F
396
Growing degree days, base 40°F
4,084
Growing degree days, base 45°F
3,097
Growing degree days, base 50°F
2,227
Growing degree days, base 55°F
1,479
Growing degree days, base 60°F
861

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,56500
February1,30100
March1,059010
April640146
May31618209
June7483460
July23149590
August39109535
September20634294
October572375
November96607
December1,37200

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 17.8 km from Viola. 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 USC00478827 (Viroqua). Public domain.