West climate

West Frost Dates and Growing Season

NOAA 1991-2020 normals for Hillsboro, 23.9 km from West, elevation 550 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Hillsboro. 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 21 and the first fall freeze around November 10, a growing season of about 235 days.

Median at 36°F
last April 2, first November 3
Median at 32°F
last March 21, first November 10
Median at 28°F
last March 9, first November 22

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

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°F236228223218213209204198190
32°F261252245240235230225219209
28°F286276269263257252246239231
24°F323308301294287281272264253
20°F360345335327318308301294280
16°F365365365365357346337328313

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
93% of years
16°F or colder
66% 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
2,257
Cooling degree days, base 65°F
2,675
Growing degree days, base 40°F
9,657
Growing degree days, base 45°F
7,986
Growing degree days, base 50°F
6,434
Growing degree days, base 55°F
5,029
Growing degree days, base 60°F
3,772

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January577271
February4207118
March26725265
April9395456
May13264716
June0473922
July06011,066
August06171,082
September4401847
October72158555
November28728240
December524595

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 23.9 km from West. 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 USC00414182 (Hillsboro). Public domain.