A fairly vigorous cool front swept through Deep South Texas early on December 12th, followed by strong high pressure with Canadian roots but not truly frigid air to arrive later on the 12th into the 13th. Clear and relatively calm conditions overnight allowed temperatures to fall near or just below freezing in rural Deep South Texas.  In locations where the temperature remained just above freezing, dew points remained in the teens, and prolonged low wet bulb temperatures in the mid 20s likely created a proxy freeze for tender vegetation in neighborhoods and towns.
The very dry, cold morning further cured fine and medium fuels (grasses and brush); the freeze was the fourth of the season in a little more than two weeks.

Frost/Freeze in ZAPATA, TEXAS
From 13-DEC-10 02:00:00 to 13-DEC-10 09:00:00 (CST-6)
Property damage: 0.00K
Reported by: COOP Observer

Freezing temperatures reached the Zapata County Airport in Medina by 2 AM, and would continue until around 9 AM before rising above 32 degrees.  Low temperatures fell to 26 degrees. Temperatures failed to fall below freezing in exposed locations, such as the Bustamante Gas Plant near Escobas. Along the Rio Grande, the Remote Automated Weather Station near Falcon Lake, just south of the Zapata/Starr County line, recorded four hours of freezing temperatures with a low of 31.
The impressively low overnight dew points, dipping into the low to mid teens, supported wet bulb temperatures in the low to mid 20s for four to seven hours after midnight on the 13th; prolonged low wet bulb temperatures are known to create a proxy freeze to unprotected, cold weather sensitive tender vegetation.

Frost/Freeze in STARR, TEXAS
From 13-DEC-10 04:00:00 to 13-DEC-10 08:00:00 (CST-6)
Property damage: 0.00K
Reported by: COOP Observer

Along the Rio Grande, the Remote Automated Weather Station near Falcon Lake, just south of the Zapata/Starr County line, recorded four hours of freezing temperatures with a low of 31, and the cooperative observation at Rio Grande City also fell to 31 degrees, with unknown duration.  The cooperative location at Falcon Dam (near border of Zapata County), however, remained several degrees above freezing, bottoming out at 35 degrees.  Proxy data and known drainage locations support most of Starr County falling to or just below freezing.
The impressively low overnight dew points, dipping into the mid teens, supported wet bulb temperatures in the mid 20s for four to seven hours after midnight on the 13th; prolonged low wet bulb temperatures are known to create a proxy freeze to unprotected, cold weather sensitive tender vegetation.

Frost/Freeze in BROOKS, TEXAS
From 13-DEC-10 04:00:00 to 13-DEC-10 08:00:00 (CST-6)
Property damage: 0.00K
Reported by: COOP Observer

The cooperative observer at the Hollywood Hunting Camp just west of Falfurrias recorded a low of 27 degrees.  Proxy locations in Kenedy County (Lebh Shomea House of Prayer, 30) and northern Hidalgo County (Lower Rio Grande Valley National Wildlife Refuge near San Manuel, 29, for three hours) support several hours of freezing temperatures across the Brooks County brush country.  In addition, dew points in the upper teens to lower 20s supported wet bulb readings in the mid to upper 20s.  Prolonged low wet bulb temperatures are known to create a proxy freeze to unprotected tender vegetation.

Frost/Freeze in JIM HOGG, TEXAS
From 13-DEC-10 04:00:00 to 13-DEC-10 08:00:00 (CST-6)
Property damage: 0.00K
Reported by: COOP Observer

Though air temperatures failed to reach 32 degrees at the Jim Hogg County Airport or the Hebbronville cooperative station in town, dew points in the mid teens, as well as nearby observations of freezing temperatures in Zapata, near Falfurrias (Brooks County), and in southern Starr County argue for several hours of freezing temperatures in central and southern portions of Jim Hogg County.
The impressively low overnight dew points supported wet bulb temperatures in the mid 20s for four to seven hours after midnight on the 13th; prolonged low wet bulb temperatures are known to create a proxy freeze to unprotected, cold weather sensitive tender vegetation.

Frost/Freeze in KENEDY, TEXAS
From 13-DEC-10 04:00:00 to 13-DEC-10 08:00:00 (CST-6)
Property damage: 0.00K
Reported by: COOP Observer

The cooperative observer at Sarita recorded a low temperature of 30 degrees around or just before daybreak; similar or lower temperatures were likely at Armstrong, whose observation was missing as of this writing. Proxy locations at the Lower Rio Grande Valley National Wildlife Refuge (10 miles southwest of the Kenedy/Hidalgo line) and Falfurrias cooperative station at the Hollywood Hunting Camp just west of town (27) support four hours of freezing temperatures across most of the King Ranch.