Ames climate

Ames Frost Dates and Growing Season

NOAA 1991-2020 normals for Ames Muni AP, 4.8 km from Ames, elevation 930 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Ames Muni AP. 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 26 and the first fall freeze around October 8, a growing season of about 164 days.

Median at 36°F
last May 5, first September 28
Median at 32°F
last April 26, first October 8
Median at 28°F
last April 14, first October 19

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

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°F163157153149146142138133127
32°F184178172168164160155150144
28°F205198193189184180176172164
24°F227220214209204201197192184
20°F247239233229225220216210201
16°F266260255249244240235229222

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
6,749
Cooling degree days, base 65°F
786
Growing degree days, base 40°F
5,117
Growing degree days, base 45°F
4,011
Growing degree days, base 50°F
3,021
Growing degree days, base 55°F
2,148
Growing degree days, base 60°F
1,400

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,40100
February1,13701
March867125
April4744105
May18651342
June21187616
July4263724
August12196649
September12274407
October44810136
November843016
December1,23401

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 4.8 km from Ames. 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 USW00094989 (Ames Muni AP). Public domain.