Wapello climate

Wapello Frost Dates and Growing Season

NOAA 1991-2020 normals for New Boston Dam 17, 10.7 km from Wapello, elevation 548 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for New Boston Dam 17. 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 14 and the first fall freeze around October 24, a growing season of about 190 days.

Median at 36°F
last April 27, first October 14
Median at 32°F
last April 14, first October 24
Median at 28°F
last April 5, first November 1

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

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 30Oct 4Oct 7Oct 11Oct 14Oct 16Oct 19Oct 21Oct 26
32°FOct 9Oct 16Oct 19Oct 22Oct 24Oct 26Oct 28Oct 31Nov 4
28°FOct 21Oct 26Oct 29Oct 31Nov 1Nov 4Nov 7Nov 11Nov 17
24°FOct 31Nov 3Nov 6Nov 9Nov 12Nov 15Nov 19Nov 23Nov 29
20°FNov 7Nov 12Nov 16Nov 20Nov 23Nov 27Nov 30Dec 4Dec 10
16°FNov 16Nov 21Nov 26Nov 29Dec 1Dec 4Dec 8Dec 13Dec 20

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°F188181176173168164160154147
32°F209203199195190185181175169
28°F232225220214210207203198189
24°F254246241236232227223218211
20°F276267262256252247242237229
16°F291283278273268263258253246

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
6,023
Cooling degree days, base 65°F
1,032
Growing degree days, base 40°F
5,664
Growing degree days, base 45°F
4,488
Growing degree days, base 50°F
3,439
Growing degree days, base 55°F
2,509
Growing degree days, base 60°F
1,704

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,28900
February1,05002
March804133
April4227132
May15269389
June16232666
July2332795
August4265725
September82110480
October36316185
November731029
December1,10803

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 10.7 km from Wapello. 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 USC00116080 (New Boston Dam 17). Public domain.