Westerly climate

Westerly Frost Dates and Growing Season

NOAA 1991-2020 normals for Westerly State AP, 3.9 km from Westerly, elevation 81 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Westerly State 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 11 and the first fall freeze around October 31, a growing season of about 201 days.

Median at 36°F
last April 27, first October 17
Median at 32°F
last April 11, first October 31
Median at 28°F
last March 29, first November 11

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

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 8Oct 11Oct 14Oct 17Oct 21Oct 23Oct 27Nov 1
32°FOct 16Oct 21Oct 25Oct 28Oct 31Nov 1Nov 4Nov 7Nov 12
28°FOct 28Nov 1Nov 5Nov 8Nov 11Nov 14Nov 17Nov 21Nov 28
24°FNov 10Nov 15Nov 19Nov 22Nov 25Nov 28Dec 1Dec 4Dec 10
20°FNov 22Nov 28Dec 1Dec 4Dec 7Dec 11Dec 16Dec 20Dec 25
16°FDec 2Dec 6Dec 12Dec 18Dec 21Dec 24Dec 28Jan 3Jan 11

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°F195187182178173169166161155
32°F221214209205201197193188181
28°F250242236232227223219214207
24°F275267262257252249244239233
20°F297289283278275270266260253
16°F321312306302297292287281274

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
5,249
Cooling degree days, base 65°F
727
Growing degree days, base 40°F
5,379
Growing degree days, base 45°F
4,102
Growing degree days, base 50°F
3,008
Growing degree days, base 55°F
2,087
Growing degree days, base 60°F
1,327

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,02301
February88301
March78708
April484166
May22114263
June42108516
July1273736
August4233694
September6588473
October31511196
November573045
December849010

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 3.9 km from Westerly. 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 USW00014794 (Westerly State AP). Public domain.