Watertown climate

Watertown Frost Dates and Growing Season

NOAA 1991-2020 normals for Watertown Wwtp, 2.4 km from Watertown, elevation 825 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Watertown Wwtp. 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 28 and the first fall freeze around October 12, a growing season of about 167 days.

Median at 36°F
last May 9, first October 2
Median at 32°F
last April 28, first October 12
Median at 28°F
last April 16, first October 25

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 16May 12May 9May 5May 2Apr 30Apr 25
32°FMay 13May 7May 3Apr 30Apr 28Apr 25Apr 22Apr 18Apr 14
28°FApr 30Apr 27Apr 23Apr 19Apr 16Apr 13Apr 10Apr 7Apr 3
24°FApr 19Apr 13Apr 10Apr 7Apr 5Apr 3Apr 1Mar 28Mar 22
20°FApr 10Apr 5Apr 2Mar 31Mar 28Mar 25Mar 21Mar 17Mar 12
16°FApr 1Mar 29Mar 25Mar 22Mar 19Mar 16Mar 13Mar 10Mar 5

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 20Sep 24Sep 27Sep 30Oct 2Oct 4Oct 7Oct 10Oct 15
32°FSep 28Oct 3Oct 6Oct 10Oct 12Oct 16Oct 18Oct 22Oct 27
28°FOct 8Oct 14Oct 19Oct 22Oct 25Oct 27Oct 30Nov 1Nov 6
24°FOct 22Oct 28Oct 31Nov 2Nov 5Nov 8Nov 11Nov 14Nov 19
20°FNov 2Nov 6Nov 9Nov 13Nov 15Nov 18Nov 21Nov 25Nov 30
16°FNov 8Nov 14Nov 18Nov 21Nov 24Nov 26Nov 30Dec 2Dec 8

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°F164158153149145141137132125
32°F186180176171167164160153148
28°F210203198195191187183177170
24°F233226220216213209205201195
20°F253246241236232228223219213
16°F269262258253249244240235229

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
7,339
Cooling degree days, base 65°F
578
Growing degree days, base 40°F
4,557
Growing degree days, base 45°F
3,511
Growing degree days, base 50°F
2,588
Growing degree days, base 55°F
1,789
Growing degree days, base 60°F
1,113

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,44300
February1,20900
March989112
April591259
May27033256
June53125522
July10203657
August23154597
September15256362
October4856109
November863013
December1,25101

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 2.4 km from Watertown. 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 USC00478919 (Watertown Wwtp). Public domain.