New Haven climate

New Haven Frost Dates and Growing Season

NOAA 1991-2020 normals for New Haven Tweed AP, 6 km from New Haven, elevation 3 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for New Haven Tweed 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 17 and the first fall freeze around October 27, a growing season of about 193 days.

Median at 36°F
last April 30, first October 15
Median at 32°F
last April 17, first October 27
Median at 28°F
last April 4, first November 6

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 12May 7May 4May 2Apr 30Apr 27Apr 24Apr 21Apr 17
32°FMay 1Apr 26Apr 22Apr 20Apr 17Apr 15Apr 11Apr 8Apr 2
28°FApr 18Apr 13Apr 9Apr 6Apr 4Apr 2Mar 31Mar 28Mar 22
24°FApr 5Apr 2Mar 31Mar 28Mar 25Mar 20Mar 17Mar 13Mar 7
20°FMar 30Mar 25Mar 19Mar 16Mar 13Mar 10Mar 6Mar 1Feb 24
16°FMar 22Mar 14Mar 10Mar 6Mar 2Feb 27Feb 23Feb 17Feb 9

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 4Oct 6Oct 9Oct 13Oct 15Oct 18Oct 22Oct 26Nov 1
32°FOct 11Oct 16Oct 20Oct 24Oct 27Oct 30Nov 1Nov 4Nov 8
28°FOct 22Oct 28Nov 1Nov 3Nov 6Nov 9Nov 12Nov 16Nov 21
24°FNov 1Nov 7Nov 12Nov 15Nov 19Nov 23Nov 27Dec 1Dec 6
20°FNov 15Nov 22Nov 27Dec 1Dec 4Dec 8Dec 12Dec 17Dec 24
16°FDec 1Dec 7Dec 11Dec 16Dec 20Dec 23Dec 28Jan 2Jan 10

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°F189182178174170166163158152
32°F211205201197193189185180174
28°F236228222218215211207202195
24°F263256250244240235230225217
20°F289281275271266261256250242
16°F314306300296290285280274264

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
5,455
Cooling degree days, base 65°F
765
Growing degree days, base 40°F
5,319
Growing degree days, base 45°F
4,086
Growing degree days, base 50°F
3,028
Growing degree days, base 55°F
2,124
Growing degree days, base 60°F
1,368

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,06800
February92300
March82007
April494164
May21515271
June36121536
July2277741
August3246708
September6393480
October33110185
November611031
December89004

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 6 km from New Haven. 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 USW00014758 (New Haven Tweed AP). Public domain.