Somervell County climate

Somervell County Frost Dates and Growing Season

NOAA 1991-2020 normals for Rainbow, 7.8 km from Somervell County, elevation 648 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Rainbow. 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 28 and the first fall freeze around November 7, a growing season of about 225 days.

Median at 36°F
last April 9, first October 28
Median at 32°F
last March 28, first November 7
Median at 28°F
last March 11, first November 18

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 27Apr 21Apr 18Apr 13Apr 9Apr 5Apr 1Mar 28Mar 21
32°FApr 19Apr 12Apr 6Apr 1Mar 28Mar 24Mar 19Mar 12Mar 5
28°FApr 5Mar 28Mar 22Mar 16Mar 11Mar 7Mar 4Feb 27Feb 20
24°FMar 20Mar 12Mar 7Mar 3Feb 28Feb 22Feb 16Feb 8Jan 31
20°FMar 8Mar 1Feb 21Feb 13Feb 6Feb 1Jan 29Jan 21Jan 6
16°FFeb 22Feb 10Feb 2Jan 30Jan 24Jan 19Jan 12Jan 1Dec 20

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 16Oct 20Oct 23Oct 26Oct 28Oct 31Nov 3Nov 7Nov 13
32°FOct 22Oct 27Nov 1Nov 3Nov 7Nov 10Nov 15Nov 19Nov 25
28°FOct 31Nov 5Nov 10Nov 15Nov 18Nov 23Nov 27Dec 1Dec 6
24°FNov 9Nov 17Nov 23Nov 28Dec 1Dec 5Dec 10Dec 17Dec 30
20°FNov 22Dec 1Dec 5Dec 12Dec 19Dec 28Jan 2Jan 9Jan 19
16°FDec 8Dec 16Dec 24Dec 31Jan 4Jan 12Jan 18Jan 26Feb 3

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°F229220214208203198194187181
32°F252244237231225220215208197
28°F280270263257252247241234223
24°F311300292285280274267260250
20°F351335327319311305297289277
16°F365365364353345338332322307

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
95% of years
16°F or colder
70% 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
2,575
Cooling degree days, base 65°F
2,513
Growing degree days, base 40°F
9,217
Growing degree days, base 45°F
7,594
Growing degree days, base 50°F
6,107
Growing degree days, base 55°F
4,762
Growing degree days, base 60°F
3,560

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January645256
February469598
March30027241
April11593436
May19259705
June0458907
July06041,069
August05861,051
September6348792
October103108475
November33121204
December587373

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 7.8 km from Somervell 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 USC00417388 (Rainbow). Public domain.