Sandy climate

Sandy Frost Dates and Growing Season

NOAA 1991-2020 normals for Headworks Portland Wtr B, 10.1 km from Sandy, elevation 748 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Headworks Portland Wtr B. 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 27 and the first fall freeze around November 18, a growing season of about 239 days.

Median at 36°F
last April 26, first October 29
Median at 32°F
last March 27, first November 18
Median at 28°F
last February 14, first December 9

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 12May 6May 2Apr 30Apr 26Apr 22Apr 19Apr 14Apr 7
32°FApr 20Apr 10Apr 3Mar 30Mar 27Mar 21Mar 13Mar 5Feb 26
28°FMar 12Mar 3Feb 25Feb 20Feb 14Feb 6Jan 30Jan 19Jan 2
24°FFeb 21Feb 13Feb 3Jan 26Jan 16Jan 6Dec 31Dec 21Dec 9
20°FFeb 21Feb 8Jan 23Jan 11Jan 1Dec 26Dec 19Dec 11Dec 3
16°F–––––––––

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 12Oct 18Oct 21Oct 24Oct 29Nov 1Nov 5Nov 10Nov 18
32°FOct 26Nov 3Nov 8Nov 13Nov 18Nov 24Nov 29Dec 3Dec 10
28°FNov 12Nov 22Nov 30Dec 3Dec 9Dec 15Dec 24Jan 2Jan 19
24°FNov 29Dec 5Dec 13Dec 21Dec 29Jan 3Jan 13Jan 25Feb 9
20°FDec 1Dec 7Dec 13Dec 19Dec 24Jan 1Jan 13Jan 31Feb 17
16°F–––––––––

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°F212203195190186181174169160
32°F274261253246239232224215205
28°F344330319311303294284275261
24°F365365365360350341333322310
20°F365365365365365365365351334
16°F365365365365365365365365365

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
97% of years
24°F or colder
65% of years
20°F or colder
31% of years
16°F or colder
9% 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
5,144
Cooling degree days, base 65°F
209
Growing degree days, base 40°F
4,417
Growing degree days, base 45°F
3,030
Growing degree days, base 50°F
1,960
Growing degree days, base 55°F
1,143
Growing degree days, base 60°F
560

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January78900
February65703
March631015
April490153
May3217172
June18918281
July6472473
August5178493
September14231340
October3873119
November621012
December80300

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 10.1 km from Sandy. 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 USC00353770 (Headworks Portland Wtr B). Public domain.