Opal climate

Opal Frost Dates and Growing Season

NOAA 1991-2020 normals for Warrenton 3 Se, 7.2 km from Opal, elevation 500 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Warrenton 3 Se. 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 April 9 and the first fall freeze around November 1, a growing season of about 205 days.

Median at 36°F
last April 22, first October 21
Median at 32°F
last April 9, first November 1
Median at 28°F
last March 29, 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°FMay 10May 4Apr 30Apr 25Apr 22Apr 19Apr 16Apr 12Apr 7
32°FApr 28Apr 20Apr 15Apr 12Apr 9Apr 6Apr 4Mar 31Mar 26
28°FApr 11Apr 6Apr 3Mar 31Mar 29Mar 26Mar 22Mar 18Mar 13
24°FMar 31Mar 26Mar 22Mar 19Mar 17Mar 14Mar 11Mar 5Feb 28
20°FMar 22Mar 19Mar 14Mar 11Mar 7Mar 3Feb 28Feb 23Feb 16
16°FMar 17Mar 10Mar 4Feb 28Feb 25Feb 19Feb 12Feb 5Jan 30

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 8Oct 12Oct 16Oct 19Oct 21Oct 24Oct 26Oct 29Nov 2
32°FOct 18Oct 23Oct 27Oct 29Nov 1Nov 3Nov 5Nov 9Nov 14
28°FNov 1Nov 5Nov 7Nov 11Nov 14Nov 16Nov 19Nov 24Dec 1
24°FNov 10Nov 15Nov 18Nov 23Nov 27Dec 1Dec 3Dec 7Dec 12
20°FNov 20Nov 27Dec 1Dec 4Dec 8Dec 12Dec 17Dec 23Dec 30
16°FDec 4Dec 10Dec 16Dec 20Dec 24Dec 28Jan 1Jan 8Jan 18

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°F202195190186182178174167159
32°F226218214209205201197191184
28°F251243238234229226221217211
24°F276268262259254250245241233
20°F304296290284279273267262252
16°F329321313307303298292286276

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
4,685
Cooling degree days, base 65°F
1,018
Growing degree days, base 40°F
6,148
Growing degree days, base 45°F
4,817
Growing degree days, base 50°F
3,630
Growing degree days, base 55°F
2,603
Growing degree days, base 60°F
1,731

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January97609
February80907
March662252
April32616185
May13758389
June20199628
July1321786
August2279742
September48126528
October28416226
November560164
December859015

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 7.2 km from Opal. 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 USC00448888 (Warrenton 3 Se). Public domain.