Green Valley climate

Green Valley Frost Dates and Growing Season

NOAA 1991-2020 normals for Mason City 4SE, 27.1 km from Green Valley, elevation 600 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Mason City 4SE. 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 17 and the first fall freeze around October 18, a growing season of about 182 days.

Median at 36°F
last April 28, first October 7
Median at 32°F
last April 17, first October 18
Median at 28°F
last April 6, first October 29

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 15May 8May 4May 1Apr 28Apr 25Apr 22Apr 19Apr 14
32°FMay 4Apr 28Apr 23Apr 20Apr 17Apr 14Apr 11Apr 7Apr 4
28°FApr 20Apr 15Apr 12Apr 8Apr 6Apr 3Apr 1Mar 29Mar 22
24°FApr 11Apr 5Apr 3Mar 31Mar 29Mar 25Mar 22Mar 18Mar 12
20°FApr 3Mar 30Mar 27Mar 22Mar 19Mar 16Mar 12Mar 8Mar 1
16°FMar 27Mar 21Mar 17Mar 14Mar 10Mar 7Mar 3Feb 28Feb 21

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 23Sep 27Oct 1Oct 5Oct 7Oct 9Oct 12Oct 15Oct 20
32°FOct 4Oct 10Oct 13Oct 16Oct 18Oct 21Oct 23Oct 26Oct 30
28°FOct 15Oct 21Oct 24Oct 27Oct 29Oct 31Nov 2Nov 5Nov 9
24°FOct 25Oct 29Nov 1Nov 3Nov 5Nov 8Nov 10Nov 14Nov 18
20°FNov 2Nov 5Nov 9Nov 12Nov 15Nov 18Nov 21Nov 24Nov 30
16°FNov 9Nov 13Nov 17Nov 21Nov 24Nov 28Dec 2Dec 5Dec 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°F181174170165162158153146140
32°F202196191186182178173168161
28°F221214210206203199195190183
24°F243235229225221217213209202
20°F264256249244240236231226219
16°F284275270264259254250244235

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
5,821
Cooling degree days, base 65°F
1,006
Growing degree days, base 40°F
5,749
Growing degree days, base 45°F
4,555
Growing degree days, base 50°F
3,481
Growing degree days, base 55°F
2,527
Growing degree days, base 60°F
1,695

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,25102
February1,01803
March774133
April37810158
May13581416
June16228663
July1308772
August6248707
September73112491
October34818199
November729134
December1,09305

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 27.1 km from Green Valley. 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 USC00115413 (Mason City 4SE). Public domain.