Greenwich climate

Greenwich Frost Dates and Growing Season

NOAA 1991-2020 normals for Mansfield Lahm Muni AP, 23.3 km from Greenwich, elevation 1295 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Mansfield Lahm Muni AP. 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 22, a growing season of about 177 days.

Median at 36°F
last May 6, first October 9
Median at 32°F
last April 26, first October 22
Median at 28°F
last April 16, first November 2

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 17May 13May 9May 6May 2Apr 30Apr 26Apr 22
32°FMay 12May 6May 2Apr 29Apr 26Apr 23Apr 20Apr 18Apr 14
28°FMay 2Apr 25Apr 21Apr 19Apr 16Apr 13Apr 9Apr 5Apr 1
24°FApr 19Apr 14Apr 9Apr 5Apr 3Mar 31Mar 29Mar 24Mar 18
20°FApr 8Apr 3Mar 31Mar 28Mar 24Mar 21Mar 18Mar 14Mar 9
16°FMar 30Mar 25Mar 21Mar 18Mar 15Mar 12Mar 8Mar 4Feb 26

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 26Oct 1Oct 4Oct 6Oct 9Oct 11Oct 15Oct 18Oct 23
32°FOct 6Oct 12Oct 15Oct 19Oct 22Oct 24Oct 27Oct 31Nov 4
28°FOct 19Oct 24Oct 28Oct 31Nov 2Nov 4Nov 8Nov 11Nov 15
24°FNov 1Nov 4Nov 7Nov 10Nov 12Nov 15Nov 18Nov 23Nov 29
20°FNov 8Nov 13Nov 16Nov 20Nov 24Nov 27Dec 1Dec 6Dec 12
16°FNov 16Nov 22Nov 27Dec 1Dec 4Dec 8Dec 12Dec 18Dec 23

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°F175168163159155151147142136
32°F198191185181177174170164158
28°F221214209205201197193188180
24°F245238232228223219215210202
20°F267257252247243239233229223
16°F290281275269264259254248240

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
5,983
Cooling degree days, base 65°F
751
Growing degree days, base 40°F
5,271
Growing degree days, base 45°F
4,090
Growing degree days, base 50°F
3,047
Growing degree days, base 55°F
2,140
Growing degree days, base 60°F
1,371

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,19203
February1,00505
March844130
April4687117
May19955334
June38158570
July5239699
August11197651
September10181433
October38612165
November705035
December1,02906

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 23.3 km from Greenwich. 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 USW00014891 (Mansfield Lahm Muni AP). Public domain.