Zavala County climate

Zavala County Frost Dates and Growing Season

NOAA 1991-2020 normals for Crystal City, 21.8 km from Zavala County, elevation 580 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Crystal City. 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 February 10 and the first fall freeze around December 10, a growing season of about 307 days.

Median at 36°F
last February 28, first November 28
Median at 32°F
last February 10, first December 10
Median at 28°F
last January 20, first December 26

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°FMar 18Mar 12Mar 8Mar 4Feb 28Feb 24Feb 19Feb 12Feb 2
32°FMar 9Mar 3Feb 25Feb 18Feb 10Feb 4Jan 29Jan 21Jan 6
28°FFeb 28Feb 16Feb 5Jan 29Jan 20Jan 10Jan 3Dec 28Dec 15
24°FFeb 13Feb 1Jan 18Jan 8Jan 4Dec 31Dec 28Dec 20Dec 12
20°F–––––––––
16°F–––––––––

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°FNov 8Nov 15Nov 20Nov 24Nov 28Dec 2Dec 6Dec 11Dec 19
32°FNov 19Nov 27Dec 2Dec 6Dec 10Dec 17Dec 23Dec 31Jan 9
28°FDec 1Dec 6Dec 13Dec 19Dec 26Jan 1Jan 7Jan 20Feb 6
24°FDec 7Dec 15Dec 22Dec 28Jan 1Jan 5Jan 10Jan 23Feb 5
20°F–––––––––
16°F–––––––––

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°F308296288281275269262256246
32°F345333323315307300292282270
28°F365365363354346338330318302
24°F365365365365365365365357341
20°F365365365365365365365365365
16°F365365365365365365365365365

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
98% of years
28°F or colder
77% of years
24°F or colder
31% of years
20°F or colder
2% of years
16°F or colder
0% 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
990
Cooling degree days, base 65°F
3,838
Growing degree days, base 40°F
11,978
Growing degree days, base 45°F
10,170
Growing degree days, base 50°F
8,406
Growing degree days, base 55°F
6,737
Growing degree days, base 60°F
5,208

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January31012202
February17141300
March73135531
April13281719
May1476941
June06151,065
July06641,128
August06961,161
September0516966
October16304754
November12281415
December28518225

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 21.8 km from Zavala 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 USC00412160 (Crystal City). Public domain.