Silverton climate

Silverton Frost Dates and Growing Season

NOAA 1991-2020 normals for Silverton, 0.7 km from Silverton, elevation 408 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Silverton. 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 28 and the first fall freeze around November 10, a growing season of about 227 days.

Median at 36°F
last April 25, first October 26
Median at 32°F
last March 28, first November 10
Median at 28°F
last February 25, first November 28

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 11May 5May 1Apr 28Apr 25Apr 20Apr 16Apr 11Apr 5
32°FApr 19Apr 10Apr 4Mar 31Mar 28Mar 23Mar 17Mar 10Mar 1
28°FMar 23Mar 13Mar 5Feb 28Feb 25Feb 19Feb 12Feb 2Jan 18
24°FFeb 26Feb 20Feb 12Feb 2Jan 23Jan 12Jan 1Dec 22Dec 12
20°FFeb 19Feb 10Jan 25Jan 10Jan 1Dec 26Dec 16Dec 10Dec 1
16°FFeb 18Feb 8Feb 1Jan 5Dec 30Dec 20Dec 13Dec 8Nov 30

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 9Oct 15Oct 20Oct 23Oct 26Oct 29Nov 1Nov 5Nov 11
32°FOct 25Oct 29Nov 2Nov 7Nov 10Nov 13Nov 19Nov 24Dec 1
28°FNov 4Nov 10Nov 17Nov 23Nov 28Dec 3Dec 8Dec 14Dec 24
24°FNov 15Nov 26Dec 2Dec 7Dec 12Dec 19Dec 28Jan 5Jan 27
20°FNov 27Dec 2Dec 8Dec 13Dec 20Dec 29Jan 3Jan 20Feb 11
16°FNov 30Dec 6Dec 10Dec 14Dec 20Dec 31Jan 18Feb 3Feb 17

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°F209199194189184179173167160
32°F260247240234227221214207198
28°F320306296287278271262254243
24°F365355344335329319311302284
20°F365365365365365356344334319
16°F365365365365365365365365343

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
86% of years
20°F or colder
48% of years
16°F or colder
18% 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
4,658
Cooling degree days, base 65°F
319
Growing degree days, base 40°F
4,990
Growing degree days, base 45°F
3,518
Growing degree days, base 50°F
2,332
Growing degree days, base 55°F
1,426
Growing degree days, base 60°F
757

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January75005
February61607
March574025
April436172
May26711219
June13833345
July32112546
August28114552
September10444390
October3542143
November588024
December77205

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 0.7 km from Silverton. 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 USC00357823 (Silverton). Public domain.