Los Indios Frost Dates and Growing Season

NOAA 1991-2020 normals for Harlingen, 18.6 km from Los Indios, elevation 38 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Harlingen. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

A freeze (32°F or colder) happens in only 31 percent of years at Harlingen, so there is no typical freeze season.

Median at 36°F: last January 21, first December 26
Median at 32°F: last January 9, first January 3

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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	Feb 28	Feb 15	Feb 3	Jan 28	Jan 21	Jan 11	Jan 5	Dec 28	Dec 17
32°F	Feb 4	Jan 28	Jan 23	Jan 14	Jan 9	Jan 5	Dec 31	Dec 24	Dec 15
28°F	–	–	–	–	–	–	–	–	–
24°F	–	–	–	–	–	–	–	–	–
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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	Nov 29	Dec 6	Dec 12	Dec 19	Dec 26	Jan 1	Jan 5	Jan 15	Feb 2
32°F	Dec 9	Dec 19	Dec 27	Jan 1	Jan 3	Jan 7	Jan 12	Jan 20	Jan 29
28°F	–	–	–	–	–	–	–	–	–
24°F	–	–	–	–	–	–	–	–	–
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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	365	365	357	348	340	334	326	314	299
32°F	365	365	365	365	365	365	365	353	338
28°F	365	365	365	365	365	365	365	365	365
24°F	365	365	365	365	365	365	365	365	365
20°F	365	365	365	365	365	365	365	365	365
16°F	365	365	365	365	365	365	365	365	365

How often it gets that cold

The share of years with at least one night at or below each temperature.

36°F or colder: 79% of years
32°F or colder: 31% of years
28°F or colder: 5% of years
24°F or colder: 0% of years
20°F or colder: 0% 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: 543
Cooling degree days, base 65°F: 4,438
Growing degree days, base 40°F: 13,023
Growing degree days, base 45°F: 11,208
Growing degree days, base 50°F: 9,413
Growing degree days, base 55°F: 7,660
Growing degree days, base 60°F: 5,991

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	179	68	372
February	97	108	438
March	42	213	637
April	8	342	785
May	0	510	975
June	0	619	1,070
July	0	674	1,139
August	0	691	1,156
September	0	551	1,001
October	5	389	850
November	55	183	580
December	157	90	411

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 18.6 km from Los Indios. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00413943 (Harlingen). Public domain.