Waterloo climate

Waterloo Frost Dates and Growing Season

NOAA 1991-2020 normals for Geneva Rsch Farm, 14 km from Waterloo, elevation 718 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Geneva Rsch 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 30 and the first fall freeze around October 21, a growing season of about 173 days.

Median at 36°F
last May 10, first October 7
Median at 32°F
last April 30, first October 21
Median at 28°F
last April 17, first November 2

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

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°F169162157154150146142138131
32°F193187181177173169164160153
28°F217211206202198194190185177
24°F240234229225222218214210205
20°F263255249246242238234229223
16°F281274268263260256250245238

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
7,006
Cooling degree days, base 65°F
475
Growing degree days, base 40°F
4,405
Growing degree days, base 45°F
3,343
Growing degree days, base 50°F
2,419
Growing degree days, base 55°F
1,630
Growing degree days, base 60°F
975

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,29901
February1,13500
March1,02508
April625352
May29027236
June7794468
July16171620
August27133570
September15545346
October4713102
November782015
December1,10401

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 km from Waterloo. 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 USC00303184 (Geneva Rsch Farm). Public domain.