Waterloo climate

Waterloo Frost Dates and Growing Season

NOAA 1991-2020 normals for Waterloo Wwtp, 0.5 km from Waterloo, elevation 800 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Waterloo Wwtp. 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 9, a growing season of about 163 days.

Median at 36°F
last May 11, first October 1
Median at 32°F
last April 30, first October 9
Median at 28°F
last April 18, first October 22

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

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°F160153149145141137133128121
32°F183176171167163159154150144
28°F205199194190186181177172165
24°F228222217213209205200195187
20°F250243238234231226222216209
16°F268261257252248244240235227

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
7,208
Cooling degree days, base 65°F
585
Growing degree days, base 40°F
4,603
Growing degree days, base 45°F
3,542
Growing degree days, base 50°F
2,611
Growing degree days, base 55°F
1,803
Growing degree days, base 60°F
1,125

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,42400
February1,18901
March970115
April574159
May25431267
June43122530
July10208663
August19168614
September15850349
October4854100
November849013
December1,23400

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 0.5 km from Waterloo. 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 USC00478910 (Waterloo Wwtp). Public domain.