Somerville climate

Somerville Frost Dates and Growing Season

NOAA 1991-2020 normals for Moscow, 20 km from Somerville, elevation 335 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Moscow. 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 29 and the first fall freeze around November 3, a growing season of about 219 days.

Median at 36°F
last April 8, first October 24
Median at 32°F
last March 29, first November 3
Median at 28°F
last March 16, first November 13

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 24Apr 20Apr 15Apr 11Apr 8Apr 4Apr 1Mar 28Mar 22
32°FApr 16Apr 9Apr 5Apr 1Mar 29Mar 25Mar 20Mar 15Mar 9
28°FApr 5Mar 29Mar 24Mar 19Mar 16Mar 11Mar 8Mar 3Feb 27
24°FMar 23Mar 16Mar 11Mar 8Mar 5Mar 1Feb 26Feb 21Feb 12
20°FMar 13Mar 7Mar 2Feb 26Feb 21Feb 16Feb 11Feb 1Jan 24
16°FMar 4Feb 25Feb 19Feb 12Feb 5Jan 31Jan 25Jan 18Jan 7

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 11Oct 15Oct 18Oct 21Oct 24Oct 26Oct 29Nov 1Nov 4
32°FOct 21Oct 25Oct 29Nov 1Nov 3Nov 5Nov 8Nov 12Nov 20
28°FOct 30Nov 2Nov 6Nov 9Nov 13Nov 17Nov 22Nov 27Dec 3
24°FNov 8Nov 13Nov 19Nov 24Nov 28Dec 2Dec 6Dec 12Dec 20
20°FNov 16Nov 27Dec 2Dec 8Dec 13Dec 20Dec 25Dec 31Jan 8
16°FDec 6Dec 16Dec 24Dec 28Jan 1Jan 5Jan 11Jan 19Jan 31

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°F220212207203199194190185177
32°F242234229224219215210204196
28°F269259251246241236231225216
24°F299285279273267261255248240
20°F332318310303298293286277264
16°F363348338332325318310302292

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
99% of years
16°F or colder
92% 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
3,227
Cooling degree days, base 65°F
1,871
Growing degree days, base 40°F
8,053
Growing degree days, base 45°F
6,517
Growing degree days, base 50°F
5,127
Growing degree days, base 55°F
3,889
Growing degree days, base 60°F
2,802

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January766131
February597146
March40611156
April16052353
May29181617
June1359808
July0484949
August0462927
September12257694
October15958374
November4157132
December682040

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 20 km from Somerville. 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 USC00406274 (Moscow). Public domain.