Napoleon climate

Napoleon Frost Dates and Growing Season

NOAA 1991-2020 normals for Manchester, 18.4 km from Napoleon, elevation 965 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Manchester. 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 30 and the first fall freeze around October 14, a growing season of about 165 days.

Median at 36°F
last May 10, first October 3
Median at 32°F
last April 30, first October 14
Median at 28°F
last April 19, first October 27

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 26May 21May 17May 13May 10May 7May 4Apr 30Apr 26
32°FMay 16May 10May 6May 3Apr 30Apr 28Apr 25Apr 21Apr 16
28°FMay 5Apr 30Apr 26Apr 22Apr 19Apr 17Apr 14Apr 10Apr 6
24°FApr 22Apr 16Apr 13Apr 10Apr 7Apr 5Apr 3Mar 31Mar 25
20°FApr 10Apr 6Apr 3Apr 1Mar 29Mar 26Mar 22Mar 18Mar 12
16°FApr 1Mar 29Mar 26Mar 22Mar 19Mar 16Mar 12Mar 8Mar 3

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 19Sep 24Sep 28Oct 1Oct 3Oct 5Oct 8Oct 11Oct 16
32°FOct 1Oct 5Oct 8Oct 11Oct 14Oct 17Oct 20Oct 24Oct 29
28°FOct 11Oct 17Oct 21Oct 24Oct 27Oct 30Nov 1Nov 4Nov 10
24°FOct 24Oct 31Nov 2Nov 4Nov 7Nov 10Nov 14Nov 17Nov 22
20°FNov 4Nov 9Nov 13Nov 16Nov 19Nov 23Nov 26Nov 30Dec 6
16°FNov 14Nov 20Nov 24Nov 28Dec 1Dec 4Dec 7Dec 14Dec 20

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°F162156152147144139136130123
32°F185178173169165161157151144
28°F210201196192188184179174166
24°F234227222217213210205200193
20°F260251245241237232228223216
16°F282274268262258253248243235

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
6,652
Cooling degree days, base 65°F
592
Growing degree days, base 40°F
4,741
Growing degree days, base 45°F
3,641
Growing degree days, base 50°F
2,680
Growing degree days, base 55°F
1,850
Growing degree days, base 60°F
1,145

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,29100
February1,11200
March926116
April548270
May23832279
June47122525
July11204659
August16167617
September12957382
October4486117
November785014
December1,10202

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 18.4 km from Napoleon. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

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Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00205050 (Manchester). Public domain.