Irion County climate

Irion County Frost Dates and Growing Season

NOAA 1991-2020 normals for Mertzon 12NNW, 17.7 km from Irion County, elevation 2205 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Mertzon 12NNW. 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 1 and the first fall freeze around November 4, a growing season of about 215 days.

Median at 36°F
last April 12, first October 26
Median at 32°F
last April 1, first November 4
Median at 28°F
last March 19, first November 12

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 29Apr 23Apr 19Apr 16Apr 12Apr 8Apr 5Apr 1Mar 28
32°FApr 19Apr 12Apr 8Apr 4Apr 1Mar 29Mar 25Mar 19Mar 14
28°FApr 7Apr 1Mar 28Mar 24Mar 19Mar 15Mar 11Mar 7Mar 2
24°FMar 28Mar 20Mar 16Mar 11Mar 8Mar 5Feb 28Feb 24Feb 15
20°FMar 16Mar 9Mar 5Mar 1Feb 25Feb 18Feb 9Feb 1Jan 22
16°FMar 7Mar 1Feb 21Feb 9Feb 2Jan 27Jan 20Jan 11Dec 31

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 12Oct 17Oct 20Oct 23Oct 26Oct 29Nov 1Nov 4Nov 7
32°FOct 21Oct 26Oct 30Nov 1Nov 4Nov 6Nov 9Nov 13Nov 18
28°FOct 29Nov 3Nov 6Nov 9Nov 12Nov 15Nov 19Nov 24Nov 30
24°FNov 7Nov 12Nov 17Nov 21Nov 25Nov 28Dec 2Dec 6Dec 11
20°FNov 21Nov 26Dec 1Dec 4Dec 9Dec 15Dec 21Dec 28Jan 5
16°FDec 1Dec 11Dec 19Dec 25Jan 1Jan 5Jan 12Jan 19Feb 2

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°F216209204199194190186181174
32°F240230224219215210206200193
28°F264254247242237232226221215
24°F288278271266261257250244236
20°F331316306299292284276268258
16°F365356345337330322310301290

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
99% of years
16°F or colder
87% 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
2,691
Cooling degree days, base 65°F
2,313
Growing degree days, base 40°F
8,920
Growing degree days, base 45°F
7,310
Growing degree days, base 50°F
5,829
Growing degree days, base 55°F
4,502
Growing degree days, base 60°F
3,334

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January660140
February473699
March31722234
April11989429
May28267705
June0450900
July0524989
August0527992
September9300741
October109115479
November36712172
December608151

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 17.7 km from Irion County. 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 USC00415861 (Mertzon 12NNW). Public domain.