Porcupine climate

Porcupine Frost Dates and Growing Season

NOAA 1991-2020 normals for Porcupine 11 N, 17.9 km from Porcupine, elevation 2820 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Porcupine 11 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 17 and the first fall freeze around September 25, a growing season of about 130 days.

Median at 36°F
last May 28, first September 16
Median at 32°F
last May 17, first September 25
Median at 28°F
last May 7, first October 3

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°FJun 16Jun 9Jun 3May 31May 28May 25May 22May 19May 15
32°FJun 1May 27May 23May 19May 17May 14May 11May 8May 3
28°FMay 22May 17May 13May 10May 7May 4May 2Apr 29Apr 24
24°FMay 14May 7May 4May 1Apr 29Apr 26Apr 23Apr 19Apr 15
20°FMay 4Apr 30Apr 27Apr 24Apr 20Apr 16Apr 13Apr 9Apr 3
16°FApr 27Apr 22Apr 17Apr 13Apr 10Apr 6Apr 2Mar 29Mar 22

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 1Sep 5Sep 9Sep 13Sep 16Sep 18Sep 21Sep 24Sep 29
32°FSep 10Sep 15Sep 19Sep 22Sep 25Sep 28Sep 30Oct 3Oct 7
28°FSep 19Sep 25Sep 28Oct 1Oct 3Oct 5Oct 8Oct 11Oct 15
24°FSep 28Oct 2Oct 6Oct 9Oct 12Oct 15Oct 17Oct 21Oct 25
20°FOct 5Oct 10Oct 14Oct 17Oct 20Oct 22Oct 25Oct 29Nov 1
16°FOct 14Oct 19Oct 22Oct 25Oct 28Oct 31Nov 2Nov 7Nov 12

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°F1301231181141091051009483
32°F149142138134130126121116108
28°F166160156152148144140135129
24°F185178173169165161157152144
20°F205198192187183179175170162
16°F226216211206202197192187178

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
7,230
Cooling degree days, base 65°F
690
Growing degree days, base 40°F
4,573
Growing degree days, base 45°F
3,514
Growing degree days, base 50°F
2,605
Growing degree days, base 55°F
1,834
Growing degree days, base 60°F
1,191

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,28700
February1,08301
March899021
April615161
May32119216
June84106475
July17268716
August27223663
September17870359
October567383
November912012
December1,24100

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 17.9 km from Porcupine. 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 USC00396736 (Porcupine 11 N). Public domain.