Bristol climate

Bristol Frost Dates and Growing Season

NOAA 1991-2020 normals for Ferris, 11.7 km from Bristol, elevation 470 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Ferris. 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 March 12 and the first fall freeze around November 19, a growing season of about 253 days.

Median at 36°F
last March 26, first November 8
Median at 32°F
last March 12, first November 19
Median at 28°F
last March 1, first December 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°FApr 13Apr 6Apr 2Mar 30Mar 26Mar 22Mar 18Mar 12Mar 4
32°FMar 31Mar 25Mar 20Mar 16Mar 12Mar 8Mar 4Feb 28Feb 21
28°FMar 19Mar 12Mar 7Mar 4Mar 1Feb 25Feb 18Feb 7Jan 30
24°FMar 8Mar 3Feb 25Feb 17Feb 10Feb 4Jan 29Jan 20Jan 9
20°FFeb 28Feb 16Feb 9Feb 2Jan 26Jan 19Jan 11Jan 3Dec 23
16°FFeb 12Feb 4Jan 30Jan 24Jan 17Jan 10Jan 5Jan 1Dec 22

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 26Oct 30Nov 2Nov 5Nov 8Nov 12Nov 15Nov 19Nov 24
32°FNov 2Nov 7Nov 11Nov 15Nov 19Nov 22Nov 27Dec 1Dec 6
28°FNov 13Nov 19Nov 23Nov 28Dec 1Dec 5Dec 9Dec 16Dec 27
24°FNov 26Dec 2Dec 8Dec 13Dec 21Dec 28Jan 2Jan 10Jan 22
20°FDec 7Dec 14Dec 23Dec 30Jan 3Jan 8Jan 14Jan 24Feb 7
16°FDec 18Dec 28Jan 1Jan 4Jan 8Jan 13Jan 21Jan 30Feb 6

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°F252244239233228223218212204
32°F277270263258253248242235227
28°F309298291284278272266259250
24°F352339330321313305297290276
20°F365365365359350340331321305
16°F365365365365365365365353335

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
96% of years
20°F or colder
72% of years
16°F or colder
31% 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
2,285
Cooling degree days, base 65°F
2,685
Growing degree days, base 40°F
9,631
Growing degree days, base 45°F
7,961
Growing degree days, base 50°F
6,414
Growing degree days, base 55°F
5,013
Growing degree days, base 60°F
3,769

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January575372
February4207115
March26826262
April9492452
May12275729
June0483933
July06111,076
August06171,082
September3396843
October76145539
November29825227
December540585

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 11.7 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 USC00413133 (Ferris). Public domain.