A strong cold front surged through Deep South Texas and the Rio Grande Valley the morning after Thanksgiving Day, and was followed by temperatures which had fallen more than 40 degrees from record highs near or above 90 on Thanksgiving into the upper 40s during the mid morning hours of November 26th.
Clear skies, diminishing winds, and a chilly air mass set the stage for rapid overnight cooling on the 27th, and the season's first freeze set in during the pre dawn hours from the Rio Grande Plains to portions of the King Ranch in Kenedy County.  Subfreezing temperatures also squeezed into far northern Hidalgo County, which was not included based on both of the following criteria:  less than one half of the county area was not affected by the freeze, or one half of the county population was not affected by the freeze.

Frost/Freeze in ZAPATA, TEXAS
From 27-NOV-10 03:00:00 to 27-NOV-10 07:30:00 (CST-6)
Property damage: 0.00K
Reported by: AWOS

Near calm winds, clear skies, and a dry cool air mass allowed temperatures to fall steadily during the evening and overnight of November 26th and 27th.  By 130 AM, the typically colder Zapata Airport, located northeast of the Medina Addition, had fallen below freezing; the temperature would flirt with freezing with numerous observations at or below 32 through 730 AM, and a minimum temperature of 29 degrees.  The Remote Automated Weather Station at Falcon Lake, at the border of Starr and Zapata County, also fell to 29, with around 3 consecutive hours below 32 from 430 until 730 AM.

Frost/Freeze in JIM HOGG, TEXAS
From 27-NOV-10 03:00:00 to 27-NOV-10 07:30:00 (CST-6)
Property damage: 0.00K
Reported by: AWOS

Near calm winds, clear skies, and a dry cool air mass allowed temperatures to fall steadily during the evening and overnight of November 26th and 27th.  While low temperatures at Hebbronville hovered just above 32 degrees,  proxy values among known radiational cooling locations in Brooks (Hollywood Hunting Camp Cooperative), Zapata (Airport), and Starr (Falcon Lake) Counties showed temperatures falling into the upper 20s to around 30, suggesting at least 3 hours of freezing or below values across the southern two thirds of Jim Hogg County.

Frost/Freeze in STARR, TEXAS
From 27-NOV-10 03:00:00 to 27-NOV-10 07:30:00 (CST-6)
Property damage: 0.00K
Reported by: AWOS

Near calm winds, clear skies, and a dry cool air mass allowed temperatures to fall steadily during the evening and overnight of November 26th and 27th.  By 430 AM, the Remote Automated Weather Station at Falcon Lake, at the border of Starr and Zapata County, also fell below 32 degrees and would bottom out at 29, with around 3 consecutive hours below 32 from 430 until 730 AM.  Proxy observations in northern Hidalgo and Zapata County, along with a number of known radiational cool spots in central and northern Starr County, argue for a slightly longer duration of time at or below 32 degrees, estimated to start around 3 AM CST.

Frost/Freeze in KENEDY, TEXAS
From 27-NOV-10 03:00:00 to 27-NOV-10 07:30:00 (CST-6)
Property damage: 0.00K
Reported by: AWOS

Near calm winds, clear skies, and a dry cool air mass allowed temperatures to fall steadily during the evening and overnight of November 26th and 27th.  The typically well radiating soil of the King Ranch allowed the coldest temperatures of the region to be recorded, with 26 degrees at the Lebh Shomea House of Prayer east of Sarita, and 29 degrees in Armstrong (south central portion).  The Lower Rio Grande Valley National Wildlife Refuge in northeastern Hidalgo County recorded 28 degrees, less than 10 miles from the Kenedy County border, starting just before 3 AM.

Frost/Freeze in BROOKS, TEXAS
From 27-NOV-10 03:00:00 to 27-NOV-10 07:30:00 (CST-6)
Property damage: 0.00K
Reported by: AWOS

Near calm winds, clear skies, and a dry cool air mass allowed temperatures to fall steadily during the evening and overnight of November 26th and 27th.  Low temperatures at Brooks County Airport just southeast of Falfurrias hovered just above 32 degrees, while the cooperative site at the Hollywood Hunting Camp about 2 miles west of town recorded a low of 31 degrees. Proxy locations among many radiational cooling locations on the King Ranch in Kenedy County (Armstrong and east of Sarita) and in northern Hidalgo County (Lower Rio Grande Valley National Wildlife Refuge) had minimum temperatures in the upper 20s, suggesting at least 3 hours of freezing or lower values in much of Brooks County.