Hamilton climate

Hamilton Frost Dates and Growing Season

NOAA 1991-2020 normals for Keokuk Lock Dam 19, 3 km from Hamilton, elevation 527 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Keokuk Lock Dam 19. 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 10 and the first fall freeze around October 27, a growing season of about 198 days.

Median at 36°F
last April 22, first October 17
Median at 32°F
last April 10, first October 27
Median at 28°F
last April 2, first November 5

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 7May 2Apr 30Apr 25Apr 22Apr 19Apr 15Apr 12Apr 7
32°FApr 26Apr 21Apr 17Apr 13Apr 10Apr 8Apr 5Apr 3Mar 30
28°FApr 16Apr 10Apr 7Apr 4Apr 2Mar 31Mar 28Mar 22Mar 16
24°FApr 7Apr 2Mar 31Mar 27Mar 23Mar 19Mar 15Mar 11Mar 6
20°FMar 31Mar 24Mar 19Mar 16Mar 12Mar 10Mar 6Mar 3Feb 27
16°FMar 22Mar 16Mar 12Mar 9Mar 6Mar 3Mar 1Feb 25Feb 18

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°FOct 1Oct 5Oct 10Oct 14Oct 17Oct 19Oct 22Oct 25Oct 30
32°FOct 10Oct 16Oct 21Oct 24Oct 27Oct 29Nov 1Nov 3Nov 7
28°FOct 24Oct 29Nov 1Nov 3Nov 5Nov 8Nov 12Nov 15Nov 20
24°FNov 2Nov 5Nov 9Nov 12Nov 15Nov 18Nov 21Nov 25Dec 1
20°FNov 9Nov 14Nov 17Nov 21Nov 24Nov 27Dec 1Dec 4Dec 11
16°FNov 16Nov 22Nov 26Nov 30Dec 2Dec 5Dec 10Dec 15Dec 21

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°F197190185180177172168163156
32°F218212206203198194190185177
28°F241234228224220215210205198
24°F262254248244239235229224216
20°F278271266262257252247241231
16°F294286281275271267263257248

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
5,775
Cooling degree days, base 65°F
1,103
Growing degree days, base 40°F
5,847
Growing degree days, base 45°F
4,645
Growing degree days, base 50°F
3,574
Growing degree days, base 55°F
2,624
Growing degree days, base 60°F
1,796

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,24400
February1,00403
March772239
April4029147
May14473399
June15233667
July1345809
August3295756
September73128508
October33819205
November704038
December1,07402

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 3 km from Hamilton. 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 USC00134381 (Keokuk Lock Dam 19). Public domain.