Rancho Viejo Frost Dates and Growing Season

NOAA 1991-2020 normals for Brownsville, 19.5 km from Rancho Viejo, elevation 23 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Brownsville. 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 26 percent of years at Brownsville, so there is no typical freeze season.

Median at 36°F: last January 16, first December 30
Median at 32°F: last January 6, first January 2

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 18	Feb 7	Jan 30	Jan 23	Jan 16	Jan 9	Jan 5	Dec 30	Dec 19
32°F	Feb 1	Jan 21	Jan 13	Jan 9	Jan 6	Jan 1	Dec 30	Dec 21	Dec 11
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 30	Dec 7	Dec 16	Dec 24	Dec 30	Jan 4	Jan 6	Jan 14	Feb 1
32°F	Dec 8	Dec 18	Dec 24	Dec 30	Jan 2	Jan 6	Jan 9	Jan 14	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	363	356	350	342	334	326	310
32°F	365	365	365	365	365	365	365	359	347
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: 70% of years
32°F or colder: 26% of years
28°F or colder: 2% 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: 423
Cooling degree days, base 65°F: 4,542
Growing degree days, base 40°F: 13,246
Growing degree days, base 45°F: 11,426
Growing degree days, base 50°F: 9,619
Growing degree days, base 55°F: 7,843
Growing degree days, base 60°F: 6,136

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	143	76	410
February	76	119	468
March	29	225	661
April	5	356	801
May	0	527	992
June	0	618	1,068
July	0	664	1,128
August	0	683	1,149
September	0	554	1,004
October	5	406	867
November	43	210	618
December	123	106	455

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 19.5 km from Rancho Viejo. 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 USW00012919 (Brownsville). Public domain.