Bremer County climate

Bremer County Frost Dates and Growing Season

NOAA 1991-2020 normals for Tripoli, 6.5 km from Bremer County, elevation 1055 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Tripoli. 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 29 and the first fall freeze around October 9, a growing season of about 162 days.

Median at 36°F
last May 7, first September 30
Median at 32°F
last April 29, first October 9
Median at 28°F
last April 18, first October 20

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

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

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°F162156151147144141138133126
32°F182175170166162158154150143
28°F202197192187184180177170164
24°F222215210206202198194190183
20°F243236231226221217214209201
16°F260253247243239235231225218

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
7,436
Cooling degree days, base 65°F
682
Growing degree days, base 40°F
4,769
Growing degree days, base 45°F
3,718
Growing degree days, base 50°F
2,778
Growing degree days, base 55°F
1,954
Growing degree days, base 60°F
1,251

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,51700
February1,25000
March980114
April554274
May22941299
June35158573
July8232688
August19172618
September14668381
October4858117
November902012
December1,31000

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 6.5 km from Bremer County. 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 USC00138339 (Tripoli). Public domain.