Riverside climate

Riverside Frost Dates and Growing Season

NOAA 1991-2020 normals for Iowa City, 15.7 km from Riverside, elevation 640 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Iowa City. 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 9, a growing season of about 162 days.

Median at 36°F
last May 7, first October 1
Median at 32°F
last April 29, first October 9
Median at 28°F
last April 18, first October 20

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

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

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°F163158154150146142138133127
32°F185176172166162159155150143
28°F203196191186182179174169161
24°F225217212209205201196190183
20°F250241235229225221216211204
16°F268260255250245240236230224

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
6,645
Cooling degree days, base 65°F
798
Growing degree days, base 40°F
5,160
Growing degree days, base 45°F
4,047
Growing degree days, base 50°F
3,049
Growing degree days, base 55°F
2,168
Growing degree days, base 60°F
1,414

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,38100
February1,12301
March861126
April4756107
May19052342
June24174600
July4266727
August13208660
September11381422
October42710146
November824018
December1,21101

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 15.7 km from Riverside. 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 USC00134101 (Iowa City). Public domain.