Bristol County climate

Bristol County Frost Dates and Growing Season

NOAA 1991-2020 normals for Rochester, 14.5 km from Bristol County, elevation 65 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Rochester. 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 23 and the first fall freeze around October 21, a growing season of about 180 days.

Median at 36°F
last May 5, first October 9
Median at 32°F
last April 23, first October 21
Median at 28°F
last April 9, first November 3

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 20May 14May 11May 8May 5May 2Apr 30Apr 28Apr 24
32°FMay 7May 3Apr 29Apr 26Apr 23Apr 21Apr 18Apr 15Apr 10
28°FApr 23Apr 19Apr 15Apr 12Apr 9Apr 6Apr 4Apr 2Mar 30
24°FApr 8Apr 4Apr 2Mar 31Mar 30Mar 26Mar 23Mar 18Mar 14
20°FMar 31Mar 27Mar 24Mar 20Mar 17Mar 14Mar 11Mar 8Mar 3
16°FMar 24Mar 18Mar 14Mar 10Mar 7Mar 5Mar 2Feb 26Feb 19

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 27Oct 1Oct 3Oct 6Oct 9Oct 12Oct 14Oct 18Oct 23
32°FOct 6Oct 11Oct 14Oct 18Oct 21Oct 24Oct 26Oct 30Nov 4
28°FOct 19Oct 25Oct 29Nov 1Nov 3Nov 6Nov 9Nov 14Nov 20
24°FNov 4Nov 8Nov 12Nov 15Nov 18Nov 21Nov 26Nov 30Dec 4
20°FNov 15Nov 20Nov 25Nov 28Dec 1Dec 4Dec 7Dec 12Dec 19
16°FNov 27Dec 2Dec 5Dec 9Dec 13Dec 17Dec 21Dec 27Jan 2

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°F174168163159156153149143137
32°F198193188184180176172166160
28°F226219215211207203199193186
24°F256248244239235231227222215
20°F278271266261257252248243235
16°F302293287282278274270265256

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
5,870
Cooling degree days, base 65°F
630
Growing degree days, base 40°F
4,961
Growing degree days, base 45°F
3,773
Growing degree days, base 50°F
2,755
Growing degree days, base 55°F
1,892
Growing degree days, base 60°F
1,182

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,11602
February96201
March86408
April537256
May26118238
June62101489
July6237696
August10199654
September9669424
October3745150
November645033
December93805

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 14.5 km from Bristol County. 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 USC00196938 (Rochester). Public domain.