Thomas County climate

Thomas County Frost Dates and Growing Season

NOAA 1991-2020 normals for Cairo 1SW, 28.5 km from Thomas County, elevation 201 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Cairo 1SW. 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 March 11 and the first fall freeze around November 21, a growing season of about 255 days.

Median at 36°F
last March 27, first November 10
Median at 32°F
last March 11, first November 21
Median at 28°F
last February 25, first December 6

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 12Apr 6Apr 3Mar 31Mar 27Mar 23Mar 20Mar 16Mar 9
32°FMar 31Mar 24Mar 19Mar 15Mar 11Mar 7Mar 4Feb 28Feb 20
28°FMar 18Mar 11Mar 6Mar 1Feb 25Feb 20Feb 14Feb 6Jan 29
24°FMar 8Feb 28Feb 21Feb 14Feb 7Feb 2Jan 28Jan 19Jan 6
20°FFeb 25Feb 14Feb 6Feb 1Jan 28Jan 18Jan 11Jan 5Dec 28
16°FFeb 14Feb 6Jan 31Jan 29Jan 21Jan 14Jan 7Jan 1Dec 29

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 26Nov 1Nov 4Nov 7Nov 10Nov 13Nov 17Nov 22Dec 1
32°FNov 4Nov 10Nov 14Nov 18Nov 21Nov 25Dec 1Dec 5Dec 15
28°FNov 16Nov 22Nov 28Dec 1Dec 6Dec 12Dec 20Dec 30Jan 10
24°FNov 29Dec 6Dec 14Dec 23Dec 30Jan 3Jan 9Jan 16Feb 1
20°FDec 14Dec 25Dec 30Jan 4Jan 9Jan 13Jan 22Feb 1Feb 12
16°FDec 27Dec 31Jan 5Jan 10Jan 15Jan 20Jan 30Feb 4Feb 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°F255246240234230225220214206
32°F287274266260255250244238229
28°F319308299292286278271263254
24°F359342334328320312305296285
20°F365365365364352343335327313
16°F365365365365365365365359339

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
90% of years
20°F or colder
60% of years
16°F or colder
22% 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
1,756
Cooling degree days, base 65°F
2,327
Growing degree days, base 40°F
9,733
Growing degree days, base 45°F
7,986
Growing degree days, base 50°F
6,342
Growing degree days, base 55°F
4,833
Growing degree days, base 60°F
3,487

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January4775118
February3279159
March20526305
April7187468
May7266724
June0422871
July0474939
August0488953
September2360808
October51149564
November21930278
December39811155

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 28.5 km from Thomas 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 USC00091463 (Cairo 1SW). Public domain.