Hillsboro climate

Hillsboro Frost Dates and Growing Season

NOAA 1991-2020 normals for Courtland 2 Wsw, 14.3 km from Hillsboro, elevation 575 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Courtland 2 Wsw. 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 3, a growing season of about 221 days.

Median at 36°F
last April 9, first October 25
Median at 32°F
last March 28, first November 3
Median at 28°F
last March 13, first November 14

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

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 15Oct 19Oct 21Oct 24Oct 25Oct 28Oct 30Nov 1Nov 5
32°FOct 22Oct 27Oct 30Nov 1Nov 3Nov 5Nov 8Nov 12Nov 18
28°FNov 1Nov 4Nov 7Nov 10Nov 14Nov 18Nov 21Nov 27Dec 3
24°FNov 9Nov 14Nov 19Nov 24Nov 29Dec 2Dec 7Dec 13Dec 27
20°FNov 20Nov 30Dec 4Dec 9Dec 18Dec 27Jan 1Jan 6Jan 16
16°FDec 6Dec 18Dec 27Jan 1Jan 4Jan 9Jan 14Jan 21Feb 1

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°F218212207203199196192188182
32°F246237231226221216211206199
28°F272264259253247243236229221
24°F307296288280273268262254247
20°F340328319313306300292283271
16°F365361351343335329322314303

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
98% of years
16°F or colder
84% 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
3,208
Cooling degree days, base 65°F
1,684
Growing degree days, base 40°F
7,870
Growing degree days, base 45°F
6,324
Growing degree days, base 50°F
4,915
Growing degree days, base 55°F
3,671
Growing degree days, base 60°F
2,593

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January744040
February566258
March3977157
April17638323
May42158581
June0330780
July0448913
August0411876
September15233669
October16753360
November4474105
December655154

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 14.3 km from Hillsboro. 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 USW00063868 (Courtland 2 Wsw). Public domain.