Washington County climate

Washington County Frost Dates and Growing Season

NOAA 1991-2020 normals for Plymouth 5 E, 8.9 km from Washington County, elevation 20 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Plymouth 5 E. 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 31 and the first fall freeze around November 7, a growing season of about 221 days.

Median at 36°F
last April 11, first October 30
Median at 32°F
last March 31, first November 7
Median at 28°F
last March 17, first November 21

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 23Apr 19Apr 16Apr 13Apr 11Apr 8Apr 5Apr 1Mar 27
32°FApr 15Apr 9Apr 6Apr 3Mar 31Mar 28Mar 24Mar 20Mar 14
28°FApr 2Mar 29Mar 25Mar 21Mar 17Mar 13Mar 10Mar 4Feb 25
24°FMar 22Mar 16Mar 11Mar 6Mar 2Feb 26Feb 22Feb 14Feb 4
20°FMar 10Mar 2Feb 24Feb 18Feb 12Feb 5Jan 31Jan 24Jan 12
16°FFeb 25Feb 12Feb 3Jan 30Jan 26Jan 20Jan 15Jan 8Jan 2

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 16Oct 21Oct 25Oct 27Oct 30Nov 1Nov 3Nov 6Nov 11
32°FOct 25Oct 30Nov 2Nov 5Nov 7Nov 10Nov 13Nov 17Nov 23
28°FNov 4Nov 9Nov 13Nov 17Nov 21Nov 25Nov 29Dec 3Dec 11
24°FNov 17Nov 25Nov 30Dec 3Dec 8Dec 13Dec 21Dec 29Jan 5
20°FDec 2Dec 11Dec 17Dec 25Dec 31Jan 3Jan 8Jan 14Jan 25
16°FDec 18Dec 29Jan 2Jan 6Jan 11Jan 14Jan 19Jan 27Feb 5

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°F218213207203200196193189183
32°F245237231226221217213208201
28°F278267260254249244239232224
24°F310302294288282276268260252
20°F353337328320312306301292281
16°F365365365356347339334324310

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
96% of years
16°F or colder
69% 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
2,843
Cooling degree days, base 65°F
1,803
Growing degree days, base 40°F
8,247
Growing degree days, base 45°F
6,642
Growing degree days, base 50°F
5,186
Growing degree days, base 55°F
3,889
Growing degree days, base 60°F
2,759

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January659150
February526264
March39811162
April16058358
May40169594
June3346793
July0460925
August0412877
September7258700
October11974425
November36110163
December570376

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 8.9 km from Washington County. 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 USC00316853 (Plymouth 5 E). Public domain.