Rupert climate

Rupert Frost Dates and Growing Season

NOAA 1991-2020 normals for Rupert 4 N, 6.2 km from Rupert, elevation 3319 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Rupert 4 N. 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 2 and the first fall freeze around October 11, a growing season of about 160 days.

Median at 36°F
last May 13, first October 3
Median at 32°F
last May 2, first October 11
Median at 28°F
last April 21, first October 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°FMay 31May 25May 21May 17May 13May 10May 6May 2Apr 27
32°FMay 20May 14May 10May 6May 2Apr 30Apr 26Apr 21Apr 16
28°FMay 10May 4Apr 30Apr 24Apr 21Apr 17Apr 14Apr 11Apr 5
24°FApr 28Apr 20Apr 16Apr 12Apr 9Apr 5Apr 2Mar 30Mar 23
20°FApr 16Apr 10Apr 6Apr 3Mar 31Mar 28Mar 23Mar 19Mar 13
16°FApr 6Apr 2Mar 29Mar 25Mar 20Mar 17Mar 13Mar 7Feb 28

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 19Sep 24Sep 28Oct 1Oct 3Oct 6Oct 8Oct 11Oct 15
32°FSep 28Oct 3Oct 6Oct 9Oct 11Oct 14Oct 17Oct 20Oct 24
28°FOct 7Oct 13Oct 16Oct 19Oct 22Oct 25Oct 28Oct 31Nov 5
24°FOct 18Oct 24Oct 28Oct 31Nov 2Nov 5Nov 8Nov 13Nov 19
20°FNov 1Nov 4Nov 7Nov 11Nov 14Nov 17Nov 21Nov 26Dec 2
16°FNov 8Nov 12Nov 17Nov 21Nov 25Nov 30Dec 3Dec 7Dec 14

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°F161154150145141137132126118
32°F182175170165160156152146139
28°F205198193188184179174169159
24°F231223217213207203199191183
20°F255247241235230225220215208
16°F280269263257251246240233226

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
6,433
Cooling degree days, base 65°F
292
Growing degree days, base 40°F
4,489
Growing degree days, base 45°F
3,340
Growing degree days, base 50°F
2,335
Growing degree days, base 55°F
1,479
Growing degree days, base 60°F
778

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,19703
February1,00204
March857027
April5022105
May26515249
June8751416
July30102538
August3788516
September15330335
October4643117
November776021
December1,06305

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 6.2 km from Rupert. 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 USC00465875 (Rupert 4 N). Public domain.