Colchester climate

Colchester Frost Dates and Growing Season

NOAA 1991-2020 normals for La Harpe, 23 km from Colchester, elevation 690 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for La Harpe. 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 21 and the first fall freeze around October 19, a growing season of about 180 days.

Median at 36°F
last May 1, first October 8
Median at 32°F
last April 21, first October 19
Median at 28°F
last April 8, first October 28

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 15May 10May 7May 4May 1Apr 29Apr 25Apr 22Apr 17
32°FMay 5May 1Apr 27Apr 24Apr 21Apr 17Apr 14Apr 11Apr 6
28°FApr 25Apr 20Apr 16Apr 11Apr 8Apr 6Apr 3Apr 1Mar 25
24°FApr 14Apr 8Apr 4Apr 1Mar 30Mar 26Mar 22Mar 18Mar 11
20°FApr 5Mar 31Mar 28Mar 24Mar 20Mar 17Mar 13Mar 8Mar 3
16°FMar 30Mar 23Mar 19Mar 15Mar 12Mar 8Mar 5Mar 1Feb 23

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 24Sep 29Oct 2Oct 5Oct 8Oct 11Oct 14Oct 17Oct 21
32°FOct 4Oct 10Oct 14Oct 16Oct 19Oct 21Oct 23Oct 26Oct 31
28°FOct 16Oct 20Oct 23Oct 25Oct 28Oct 31Nov 2Nov 5Nov 10
24°FOct 27Oct 31Nov 1Nov 4Nov 7Nov 9Nov 12Nov 15Nov 20
20°FNov 4Nov 7Nov 10Nov 13Nov 16Nov 19Nov 22Nov 26Dec 1
16°FNov 9Nov 14Nov 18Nov 21Nov 25Nov 28Dec 1Dec 5Dec 11

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°F178172167162159154150146138
32°F199192187183180176172167161
28°F221214209205201197192188180
24°F244235230226222218214209201
20°F263255250245241236232228220
16°F281273267262257253247243235

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
6,103
Cooling degree days, base 65°F
955
Growing degree days, base 40°F
5,541
Growing degree days, base 45°F
4,375
Growing degree days, base 50°F
3,336
Growing degree days, base 55°F
2,414
Growing degree days, base 60°F
1,618

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,29100
February1,04203
March798236
April4339133
May16168381
June21207636
July2301764
August6248707
September96106464
October38115179
November753031
December1,11903

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 23 km from Colchester. 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 USC00114823 (La Harpe). Public domain.