Petroleum County climate

Petroleum County Frost Dates and Growing Season

NOAA 1991-2020 normals for Valentine, 31 km from Petroleum County, elevation 2905 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Valentine. 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 18 and the first fall freeze around September 21, a growing season of about 124 days.

Median at 36°F
last May 31, first September 10
Median at 32°F
last May 18, first September 21
Median at 28°F
last May 7, first September 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°FJun 16Jun 9Jun 5Jun 2May 31May 28May 24May 21May 17
32°FMay 31May 26May 23May 20May 18May 16May 13May 10May 7
28°FMay 18May 14May 12May 9May 7May 5May 2Apr 30Apr 25
24°FMay 9May 5May 2Apr 30Apr 27Apr 24Apr 20Apr 16Apr 10
20°FMay 1Apr 27Apr 22Apr 19Apr 14Apr 10Apr 6Apr 3Mar 29
16°FApr 23Apr 17Apr 12Apr 7Apr 3Mar 31Mar 27Mar 21Mar 14

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°FAug 27Sep 1Sep 4Sep 8Sep 10Sep 13Sep 17Sep 20Sep 23
32°FSep 7Sep 12Sep 16Sep 19Sep 21Sep 23Sep 25Sep 28Oct 2
28°FSep 17Sep 21Sep 24Sep 26Sep 29Oct 1Oct 4Oct 7Oct 12
24°FSep 24Sep 29Oct 1Oct 4Oct 7Oct 10Oct 13Oct 16Oct 21
20°FOct 1Oct 5Oct 9Oct 13Oct 16Oct 19Oct 23Oct 26Nov 1
16°FOct 8Oct 14Oct 18Oct 21Oct 25Oct 29Nov 1Nov 3Nov 9

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°F12211411010510197938779
32°F142136131128124120117113106
28°F163156151147144140136131124
24°F185178173169164160155151144
20°F210201194189184179175169161
16°F229220213208203197192185177

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
8,058
Cooling degree days, base 65°F
411
Growing degree days, base 40°F
3,880
Growing degree days, base 45°F
2,888
Growing degree days, base 50°F
2,051
Growing degree days, base 55°F
1,358
Growing degree days, base 60°F
808

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,41200
February1,17601
March98905
April660029
May3846152
June13545364
July30178612
August48156575
September24826257
October643152
November1,00205
December1,33100

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 31 km from Petroleum County. 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 USC00248498 (Valentine). Public domain.