A strong cold front brought a light freeze to portions of Deep South Texas and the Rio Grande Valley during the (mostly) pre-dawn hours on December 18th, 2019.  Temperatures fell to or below freezing in many areas just before daybreak, primarily those that were wind-protected where radiational cooling was maximized.  Durations of the freezing temperatures ranged from around two hours of distant suburbs and rural areas of the Rio Grande Valley to five hours across the northern ranchlands and Rio Grande Plains of Deep South Texas.

Frost/Freeze in ZAPATA, TEXAS
From 18-DEC-19 02:35:00 to 18-DEC-19 07:55:00 (CST-6)
Reported by: ASOS

Low temperatures fell to or below 32 degrees around 3 AM (later in unprotected areas and small cities) and continued through about 8 AM. Minimum measured and estimated temperatures ranged from the mid and upper 20s (27 at Zapata airport) to around 32 just east of Falcon International Reservoir.

Frost/Freeze in INLAND KENEDY COUNTY, TEXAS
From 18-DEC-19 03:00:00 to 18-DEC-19 08:00:00 (CST-6)
Reported by: COOP Observer

Low temperatures fell to or below 32 degrees around 3 AM (later in unprotected areas and small cities) and continued through about 8 AM. Minimum measured and estimated temperatures ranged from the mid and upper 20s (24 at Armstrong) to around 32.

Frost/Freeze in STARR, TEXAS
From 18-DEC-19 04:00:00 to 18-DEC-19 08:00:00 (CST-6)
Reported by: COOP Observer

Low temperatures fell to or below 32 degrees around 3 AM (later in unprotected areas and small cities) and continued through about 8 AM. Minimum measured and estimated temperatures ranged from about 30 to around 32 (30 at Rio Grande City).

Frost/Freeze in BROOKS, TEXAS
From 18-DEC-19 05:30:00 to 18-DEC-19 08:00:00 (CST-6)
Property damage: 0.00K
Reported by: COOP Observer

The cooperative observer at the Hollywood Hunting Camp about 3 miles west of Falfurrias recorded a minimum temperature of 26 degrees, while the Automated Weather Observing Station at Brooks County Airport  recorded a low temperature of 32 degrees for about 30 minutes around daybreak on December 18th.  The cooperative site at Linn/San Manuel in northern Hidalgo County recorded a low of 30 degrees.  Given these proxy observations and the likelihood of rural ranchland seeing temperatures between the two values for at least two hours implies a minor freeze occurred on the morning of December 18.

Frost/Freeze in NORTHERN HIDALGO COUNTY, TEXAS
From 18-DEC-19 05:30:00 to 18-DEC-19 08:00:00 (CST-6)
Property damage: 0.00K
Reported by: COOP Observer

The Automated Weather Observing Station at South Texas International Airport (11 miles north of Edinburg) recorded a low temperature of 31 degrees, with temperaturest between 31 and 32 degrees for nearly two and one half hours around daybreak on December 18th . The cooperative site at Linn/San Manuel in northern Hidalgo County recorded a low of 30 degrees, which likely lasted more than 2 hours given the proximity to the Airport.

Frost/Freeze in JIM HOGG, TEXAS
From 18-DEC-19 03:00:00 to 18-DEC-19 07:30:00 (CST-6)
Property damage: 0.00K
Reported by: RAWS

The Automated Weather Observing Station at Jim Hogg County Airport recorded several hours with temperatures at 32 degrees, and the on-site RAWS observation nearby recorded a couple of hours at 32, all during the pre-dawn through just after sunset hours.