Monona climate

Monona Frost Dates and Growing Season

NOAA 1991-2020 normals for Postville, 14.4 km from Monona, elevation 1165 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Postville. 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 1 and the first fall freeze around October 3, a growing season of about 153 days.

Median at 36°F
last May 10, first September 24
Median at 32°F
last May 1, first October 3
Median at 28°F
last April 22, first October 12

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

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°F154146143139136133130125119
32°F172165161157153150146140134
28°F193187182178174170165159152
24°F215208203199194190186180173
20°F235227222218213210206201192
16°F253246241236232228224219213

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
7,520
Cooling degree days, base 65°F
614
Growing degree days, base 40°F
4,614
Growing degree days, base 45°F
3,579
Growing degree days, base 50°F
2,659
Growing degree days, base 55°F
1,851
Growing degree days, base 60°F
1,162

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,50200
February1,25400
March1,002013
April578164
May24634278
June37139552
July9221677
August22161604
September15553358
October5086103
November897011
December1,31100

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 14.4 km from Monona. 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 USC00136766 (Postville). Public domain.