Sanders County climate

Sanders County Frost Dates and Growing Season

NOAA 1991-2020 normals for Thompson Falls Ph, 19.2 km from Sanders County, elevation 2380 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Thompson Falls Ph. 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 7 and the first fall freeze around October 4, a growing season of about 150 days.

Median at 36°F
last May 22, first September 21
Median at 32°F
last May 7, first October 4
Median at 28°F
last April 22, first October 18

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

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 7Sep 11Sep 16Sep 19Sep 21Sep 24Sep 27Sep 29Oct 3
32°FSep 21Sep 26Sep 29Oct 1Oct 4Oct 6Oct 10Oct 14Oct 19
28°FOct 2Oct 7Oct 11Oct 15Oct 18Oct 21Oct 25Oct 30Nov 5
24°FOct 14Oct 20Oct 25Oct 30Nov 2Nov 6Nov 11Nov 17Nov 24
20°FOct 24Nov 1Nov 6Nov 11Nov 16Nov 21Nov 25Nov 29Dec 6
16°FNov 2Nov 11Nov 18Nov 24Nov 27Dec 1Dec 6Dec 13Dec 24

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°F142135130126122118113108100
32°F170163158154150146143138132
28°F204197191186181175171165159
24°F247238231225220214209202194
20°F285273265259253247240234223
16°F314303293285277269262253241

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
6,671
Cooling degree days, base 65°F
391
Growing degree days, base 40°F
4,046
Growing degree days, base 45°F
2,987
Growing degree days, base 50°F
2,106
Growing degree days, base 55°F
1,377
Growing degree days, base 60°F
802

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,11400
February91400
March79403
April561036
May3207181
June15236337
July30171606
August31150585
September18126304
October560054
November88901
December1,12500

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 19.2 km from Sanders 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 USC00248211 (Thompson Falls Ph). Public domain.