Hannibal climate

Hannibal Frost Dates and Growing Season

NOAA 1991-2020 normals for Oswego, 14.7 km from Hannibal, elevation 324 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Oswego. 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 22 and the first fall freeze around October 29, a growing season of about 187 days.

Median at 36°F
last May 4, first October 13
Median at 32°F
last April 22, first October 29
Median at 28°F
last April 10, first November 10

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 19May 14May 10May 7May 4May 1Apr 29Apr 26Apr 23
32°FMay 7May 1Apr 28Apr 25Apr 22Apr 20Apr 18Apr 14Apr 9
28°FApr 22Apr 18Apr 15Apr 12Apr 10Apr 8Apr 5Apr 3Mar 31
24°FApr 11Apr 7Apr 4Apr 2Mar 31Mar 29Mar 25Mar 21Mar 17
20°FApr 3Mar 31Mar 28Mar 25Mar 22Mar 19Mar 16Mar 13Mar 9
16°FMar 29Mar 24Mar 20Mar 17Mar 15Mar 13Mar 10Mar 6Feb 28

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 29Oct 3Oct 7Oct 10Oct 13Oct 16Oct 20Oct 23Oct 30
32°FOct 9Oct 17Oct 21Oct 26Oct 29Nov 1Nov 3Nov 6Nov 11
28°FOct 29Nov 1Nov 4Nov 7Nov 10Nov 13Nov 17Nov 20Nov 26
24°FNov 7Nov 12Nov 15Nov 18Nov 21Nov 24Nov 28Dec 2Dec 7
20°FNov 16Nov 21Nov 26Nov 29Dec 2Dec 4Dec 7Dec 12Dec 17
16°FNov 26Dec 1Dec 4Dec 7Dec 11Dec 13Dec 17Dec 21Dec 27

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°F181175170165161157152147141
32°F207201195191187182178172165
28°F232226222217214210206202194
24°F256248243239235231227222216
20°F276267262257254249245240233
16°F292285279275271266261257250

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
6,499
Cooling degree days, base 65°F
587
Growing degree days, base 40°F
4,730
Growing degree days, base 45°F
3,624
Growing degree days, base 50°F
2,660
Growing degree days, base 55°F
1,834
Growing degree days, base 60°F
1,137

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,24001
February1,07201
March957010
April596360
May28026240
June68101483
July7208666
August11178632
September11365404
October4046135
November710025
December1,04303

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 14.7 km from Hannibal. 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 USC00306314 (Oswego). Public domain.