Bristol climate

Bristol Frost Dates and Growing Season

NOAA 1991-2020 normals for Newcastle, 9.8 km from Bristol, elevation 213 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Newcastle. 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 27 and the first fall freeze around October 18, a growing season of about 172 days.

Median at 36°F
last May 9, first October 5
Median at 32°F
last April 27, first October 18
Median at 28°F
last April 14, first November 1

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 24May 19May 14May 11May 9May 6May 4May 1Apr 29
32°FMay 10May 5May 2Apr 30Apr 27Apr 25Apr 22Apr 20Apr 16
28°FApr 27Apr 22Apr 19Apr 16Apr 14Apr 11Apr 9Apr 6Apr 2
24°FApr 16Apr 11Apr 7Apr 5Apr 3Apr 1Mar 30Mar 27Mar 21
20°FApr 6Apr 3Apr 1Mar 30Mar 27Mar 24Mar 20Mar 17Mar 12
16°FApr 1Mar 28Mar 25Mar 21Mar 19Mar 16Mar 13Mar 10Mar 6

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 28Oct 1Oct 3Oct 5Oct 7Oct 10Oct 13Oct 19
32°FOct 3Oct 7Oct 10Oct 14Oct 18Oct 21Oct 25Oct 29Nov 2
28°FOct 15Oct 21Oct 25Oct 29Nov 1Nov 3Nov 6Nov 9Nov 14
24°FNov 1Nov 4Nov 7Nov 10Nov 13Nov 15Nov 19Nov 22Nov 27
20°FNov 10Nov 14Nov 17Nov 20Nov 23Nov 26Nov 29Dec 1Dec 6
16°FNov 18Nov 24Nov 27Nov 30Dec 1Dec 4Dec 6Dec 11Dec 16

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°F164159155151148145140136129
32°F191184180176172168164159154
28°F217211207203199195191186179
24°F241234229225221218214210204
20°F260254250245241237233229223
16°F276269265261258254249244237

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
7,077
Cooling degree days, base 65°F
346
Growing degree days, base 40°F
4,133
Growing degree days, base 45°F
3,077
Growing degree days, base 50°F
2,166
Growing degree days, base 55°F
1,403
Growing degree days, base 60°F
793

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,32100
February1,12100
March99503
April626026
May3268172
June9950401
July15140591
August21117561
September16230322
October484180
November782010
December1,12500

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 9.8 km from Bristol. 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 USC00175675 (Newcastle). Public domain.