South Windham climate

South Windham Frost Dates and Growing Season

NOAA 1991-2020 normals for Portland Intl Jetport, 13.8 km from South Windham, elevation 45 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Portland Intl Jetport. 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 26 and the first fall freeze around October 15, a growing season of about 170 days.

Median at 36°F
last May 7, first October 4
Median at 32°F
last April 26, first October 15
Median at 28°F
last April 14, first October 27

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 20May 16May 12May 10May 7May 5May 3May 1Apr 28
32°FMay 7May 3May 1Apr 29Apr 26Apr 24Apr 22Apr 20Apr 16
28°FApr 25Apr 21Apr 19Apr 16Apr 14Apr 11Apr 9Apr 6Apr 3
24°FApr 16Apr 10Apr 7Apr 5Apr 3Apr 1Mar 30Mar 26Mar 21
20°FApr 4Apr 1Mar 30Mar 26Mar 23Mar 21Mar 17Mar 14Mar 10
16°FMar 29Mar 25Mar 21Mar 18Mar 15Mar 12Mar 10Mar 7Mar 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°FSep 24Sep 28Sep 30Oct 2Oct 4Oct 6Oct 9Oct 13Oct 17
32°FOct 2Oct 5Oct 9Oct 11Oct 15Oct 17Oct 21Oct 25Oct 30
28°FOct 14Oct 19Oct 22Oct 25Oct 27Oct 30Nov 2Nov 5Nov 9
24°FOct 26Oct 31Nov 3Nov 5Nov 8Nov 11Nov 14Nov 18Nov 23
20°FNov 8Nov 12Nov 15Nov 18Nov 21Nov 24Nov 27Dec 1Dec 5
16°FNov 18Nov 23Nov 27Nov 30Dec 1Dec 4Dec 8Dec 12Dec 18

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°F164159155152149145142138132
32°F188182177173170166162158153
28°F212206202198195192187183177
24°F239232227223220216212208202
20°F263257252247244240236231225
16°F282276271266263259255251244

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
6,795
Cooling degree days, base 65°F
447
Growing degree days, base 40°F
4,335
Growing degree days, base 45°F
3,254
Growing degree days, base 50°F
2,327
Growing degree days, base 55°F
1,551
Growing degree days, base 60°F
922

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,27100
February1,08800
March95604
April613131
May32510174
June8968430
July10176631
August16147595
September14543352
October459295
November749014
December1,07401

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 13.8 km from South Windham. 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 USW00014764 (Portland Intl Jetport). Public domain.