Harper climate

Harper Frost Dates and Growing Season

NOAA 1991-2020 normals for Harper 3ENE, 4.1 km from Harper, elevation 2110 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Harper 3ENE. 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 15 and the first fall freeze around November 15, a growing season of about 243 days.

Median at 36°F
last April 1, first November 4
Median at 32°F
last March 15, first November 15
Median at 28°F
last March 2, first November 29

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 24Apr 16Apr 10Apr 5Apr 1Mar 28Mar 22Mar 16Mar 7
32°FApr 12Apr 3Mar 28Mar 21Mar 15Mar 11Mar 5Mar 1Feb 24
28°FMar 28Mar 17Mar 11Mar 6Mar 2Feb 26Feb 22Feb 15Feb 5
24°FMar 12Mar 5Feb 28Feb 23Feb 16Feb 9Jan 31Jan 20Jan 3
20°FMar 4Feb 22Feb 13Feb 2Jan 25Jan 16Jan 7Dec 31Dec 18
16°FFeb 22Feb 12Feb 3Jan 23Jan 15Jan 7Jan 3Dec 28Dec 19

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 20Oct 24Oct 29Nov 1Nov 4Nov 7Nov 11Nov 16Nov 24
32°FOct 27Nov 2Nov 6Nov 10Nov 15Nov 20Nov 24Nov 30Dec 6
28°FNov 4Nov 12Nov 18Nov 23Nov 29Dec 3Dec 7Dec 14Dec 25
24°FNov 14Nov 23Dec 1Dec 6Dec 13Dec 21Dec 30Jan 5Jan 18
20°FNov 27Dec 6Dec 18Dec 26Jan 1Jan 5Jan 12Jan 24Feb 12
16°FDec 10Dec 21Dec 31Jan 4Jan 7Jan 14Jan 23Feb 2Feb 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°F248238230224218212206200191
32°F273262254248243236229221211
28°F308296285276270262255245234
24°F351335324314305296287277264
20°F365365365355344334325311296
16°F365365365365365365365355337

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
96% of years
20°F or colder
71% of years
16°F or colder
29% 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
2,208
Cooling degree days, base 65°F
2,139
Growing degree days, base 40°F
9,162
Growing degree days, base 45°F
7,475
Growing degree days, base 50°F
5,899
Growing degree days, base 55°F
4,471
Growing degree days, base 60°F
3,213

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January551174
February4005125
March25921262
April9384445
May18237683
June0390840
July0479944
August0486951
September5290735
October85122508
November29322233
December502299

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 4.1 km from Harper. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00413954 (Harper 3ENE). Public domain.