Washington County climate

Washington County Frost Dates and Growing Season

NOAA 1991-2020 normals for Cambridge, 16.1 km from Washington County, elevation 2650 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Cambridge. 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 May 15 and the first fall freeze around September 27, a growing season of about 134 days.

Median at 36°F
last June 3, first September 16
Median at 32°F
last May 15, first September 27
Median at 28°F
last April 28, first October 7

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°FJun 21Jun 15Jun 10Jun 7Jun 3May 30May 26May 20May 15
32°FJun 4May 29May 22May 17May 15May 11May 8May 3Apr 29
28°FMay 15May 8May 3May 1Apr 28Apr 24Apr 20Apr 15Apr 8
24°FApr 29Apr 21Apr 15Apr 10Apr 6Apr 2Mar 29Mar 23Mar 16
20°FApr 6Mar 31Mar 27Mar 21Mar 17Mar 13Mar 10Mar 6Mar 1
16°FMar 21Mar 15Mar 10Mar 7Mar 4Mar 2Feb 27Feb 23Feb 18

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 2Sep 6Sep 10Sep 13Sep 16Sep 19Sep 22Sep 25Sep 30
32°FSep 12Sep 17Sep 21Sep 24Sep 27Sep 30Oct 2Oct 5Oct 9
28°FSep 23Sep 28Oct 2Oct 4Oct 7Oct 9Oct 13Oct 17Oct 22
24°FOct 5Oct 9Oct 14Oct 17Oct 20Oct 23Oct 26Oct 31Nov 4
20°FOct 17Oct 23Oct 26Oct 31Nov 1Nov 3Nov 8Nov 13Nov 20
16°FOct 28Nov 2Nov 5Nov 9Nov 13Nov 17Nov 22Nov 26Dec 2

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°F127119114109104100959081
32°F154148143139134130126119111
28°F187179172168164159155149141
24°F220211205201195190184179171
20°F253245239234230224217211202
16°F278270264259254250244239231

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
6,734
Cooling degree days, base 65°F
693
Growing degree days, base 40°F
4,673
Growing degree days, base 45°F
3,573
Growing degree days, base 50°F
2,632
Growing degree days, base 55°F
1,843
Growing degree days, base 60°F
1,197

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,29100
February1,01500
March77705
April498053
May26113235
June9281441
July9297753
August14251702
September13551370
October514172
November90201
December1,22900

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 16.1 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 USC00101408 (Cambridge). Public domain.