Willacy County Frost Dates and Growing Season

NOAA 1991-2020 normals for Port Mansfield, 18.8 km from Willacy County, elevation 9 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Port Mansfield. 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 January 12 and the first fall freeze around January 1, a growing season of about 362 days.

Median at 36°F: last January 30, first December 19
Median at 32°F: last January 12, first January 1
Median at 28°F: last January 7, first January 5

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	Mar 3	Feb 22	Feb 12	Feb 4	Jan 30	Jan 22	Jan 14	Jan 5	Dec 24
32°F	Feb 19	Feb 7	Jan 29	Jan 19	Jan 12	Jan 7	Jan 1	Dec 25	Dec 15
28°F	Feb 9	Jan 29	Jan 18	Jan 11	Jan 7	Jan 4	Jan 1	Dec 26	Dec 15
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 24	Dec 2	Dec 7	Dec 14	Dec 19	Dec 24	Jan 1	Jan 7	Jan 22
32°F	Dec 5	Dec 15	Dec 21	Dec 27	Jan 1	Jan 5	Jan 10	Jan 20	Feb 5
28°F	Dec 14	Dec 23	Dec 31	Jan 2	Jan 5	Jan 7	Jan 11	Jan 18	Feb 3
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	352	343	334	327	319	308	299	285
32°F	365	365	365	365	362	353	345	335	323
28°F	365	365	365	365	365	365	365	365	353
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: 91% of years
32°F or colder: 56% of years
28°F or colder: 17% of years
24°F or colder: 3% 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: 674
Cooling degree days, base 65°F: 3,755
Growing degree days, base 40°F: 12,210
Growing degree days, base 45°F: 10,397
Growing degree days, base 50°F: 8,611
Growing degree days, base 55°F: 6,883
Growing degree days, base 60°F: 5,254

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	223	37	303
February	128	65	368
March	55	150	562
April	10	270	710
May	1	435	899
June	0	543	993
July	0	592	1,057
August	0	609	1,074
September	0	482	932
October	7	350	808
November	70	160	544
December	180	64	364

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 18.8 km from Willacy County. 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 USC00417184 (Port Mansfield). Public domain.