Nez Perce County climate

Nez Perce County Frost Dates and Growing Season

NOAA 1991-2020 normals for Winchester, 13.9 km from Nez Perce County, elevation 3972 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Winchester. 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 23 and the first fall freeze around September 25, a growing season of about 121 days.

Median at 36°F
last June 18, first September 8
Median at 32°F
last May 23, first September 25
Median at 28°F
last May 2, first October 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°FJul 12Jul 2Jun 27Jun 23Jun 18Jun 14Jun 10Jun 5Jun 1
32°FJun 19Jun 6Jun 1May 28May 23May 19May 15May 10May 4
28°FMay 24May 14May 10May 6May 2Apr 29Apr 26Apr 21Apr 13
24°FMay 1Apr 26Apr 19Apr 14Apr 10Apr 5Apr 1Mar 28Mar 21
20°FApr 7Apr 2Mar 28Mar 25Mar 21Mar 17Mar 13Mar 9Mar 4
16°FMar 27Mar 20Mar 15Mar 11Mar 7Mar 4Mar 1Feb 24Feb 15

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°FAug 21Aug 30Sep 2Sep 5Sep 8Sep 12Sep 17Sep 21Sep 26
32°FSep 7Sep 12Sep 17Sep 21Sep 25Sep 28Oct 1Oct 4Oct 10
28°FSep 21Sep 29Oct 2Oct 5Oct 9Oct 14Oct 17Oct 21Oct 28
24°FOct 5Oct 12Oct 18Oct 22Oct 26Oct 29Nov 1Nov 5Nov 13
20°FOct 18Oct 26Nov 1Nov 5Nov 8Nov 12Nov 16Nov 21Nov 27
16°FOct 27Nov 5Nov 10Nov 15Nov 19Nov 23Nov 27Dec 2Dec 10

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°F1049691858075706353
32°F14713813212612111610910089
28°F185174169164160154148141129
24°F222213206201196190185178167
20°F256246240235230224220213201
16°F284272266261255248242235225

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
7,552
Cooling degree days, base 65°F
140
Growing degree days, base 40°F
3,090
Growing degree days, base 45°F
2,131
Growing degree days, base 50°F
1,369
Growing degree days, base 55°F
789
Growing degree days, base 60°F
382

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,09400
February94500
March89401
April697013
May489178
June3016178
July10759418
August9961428
September28213212
October617040
November89602
December1,13000

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 13.9 km from Nez Perce 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 USC00109846 (Winchester). Public domain.