Monroe County climate

Monroe County Frost Dates and Growing Season

NOAA 1991-2020 normals for Hannibal Locks & Dam, 19.7 km from Monroe County, elevation 620 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Hannibal Locks & Dam. 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 26, a growing season of about 182 days.

Median at 36°F
last May 6, first October 15
Median at 32°F
last April 26, first October 26
Median at 28°F
last April 13, first November 3

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 22May 16May 12May 9May 6May 3Apr 30Apr 26Apr 22
32°FMay 13May 7May 2Apr 30Apr 26Apr 24Apr 21Apr 18Apr 13
28°FApr 30Apr 23Apr 19Apr 16Apr 13Apr 10Apr 6Apr 3Mar 29
24°FApr 14Apr 9Apr 5Apr 2Mar 31Mar 28Mar 24Mar 20Mar 15
20°FApr 2Mar 30Mar 25Mar 21Mar 18Mar 15Mar 12Mar 7Mar 1
16°FMar 25Mar 18Mar 15Mar 11Mar 7Mar 4Mar 1Feb 23Feb 14

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 6Oct 10Oct 12Oct 15Oct 18Oct 21Oct 23Oct 27
32°FOct 12Oct 17Oct 20Oct 23Oct 26Oct 28Oct 30Nov 1Nov 5
28°FOct 22Oct 27Oct 31Nov 1Nov 3Nov 5Nov 8Nov 12Nov 16
24°FNov 2Nov 5Nov 9Nov 12Nov 15Nov 18Nov 21Nov 26Dec 1
20°FNov 10Nov 15Nov 19Nov 23Nov 27Dec 1Dec 3Dec 9Dec 15
16°FNov 20Nov 27Dec 1Dec 5Dec 10Dec 15Dec 20Dec 25Jan 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°F179173169165161157153148141
32°F199194189185182178173169162
28°F223217213209205201197192184
24°F249242236232228224221215210
20°F280271262257252247243237231
16°F305297290284278273268262253

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
5,507
Cooling degree days, base 65°F
743
Growing degree days, base 40°F
5,419
Growing degree days, base 45°F
4,193
Growing degree days, base 50°F
3,113
Growing degree days, base 55°F
2,180
Growing degree days, base 60°F
1,387

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,10502
February92403
March780028
April4284123
May18341334
June30140560
July2239702
August4218679
September7091472
October34810177
November675029
December95805

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 19.7 km from Monroe 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 USC00333500 (Hannibal Locks & Dam). Public domain.