A true blue norther drove pure Canadian high pressure directly into South Texas and northern Mexico, beginning on November 27th and continuing through early on the 29th before the high drifted into the southeast U.S.  Extremely dry and relatively chilly air invaded Deep South Texas and the Rio Grande Valley; temperatures bottomed out in the mid 20s to lower 30s for all but the southeast corner of the Rio Grande Valley on the 28th.
The event was a rare dry freeze, as humidity through the coldest periods remained below 50 percent.  Ambient temperatures varied greatly depending on the height of the sensor taking the measurements.  At eye level, temperatures fell to or just below freezing in many areas, but remained a few degrees above freezing in others.  Just above the ground, and in wind protected hollows, temperatures fell into the 20s; local hard freezes, defined as 2 or more hours with temperatures below 28 degrees, likely occurred.  Agricultural damage was not known as of this writing.

Frost/Freeze in HIDALGO, TEXAS
From 28-NOV-11 04:00:00 to 28-NOV-11 08:00:00 (CST-6)
Property damage: 0.00K
Reported by: Mesonet

Temperatures fell below freezing in wind protected areas of Hidalgo County after midnight on the 28th, bottoming out in the mid 20s in these areas, around freezing in rural locations with less wind protection, and in the mid to upper 30s in urbanized sections from Weslaco to Mission.  The primary time for continuous subfreezing temperatures was between 4 and 8 AM, though some pockets fell to freezing as early as 2 AM.
Low temperatures included 24 degrees at both the Lower Rio Grande Valley Wildlife Refuge sites of Santa Ana (along the Rio Grande southeast of Pharr) and Linn/San Manuel (along the Willacy County line near SR 186), 31 degrees at the Climate Reference Network site along SR 186 near San Manuel, and 32 degrees at Edinburg International Airport, the San Manuel cooperative site, and near La Joya.
Agricultural damage was unknown as of early December.  However, the dry freeze and associated low wet bulb temperatures, which ranged from the upper 20s to 31 degrees even in areas where air temperatures were a few degrees above freezing, likely caused minor problems to cold sensitive crops, particularly tender tropical vegetation.  The freeze reinforced the impacts from the intense drought (Exceptional for most of the county).

Frost/Freeze in WILLACY, TEXAS
From 28-NOV-11 04:00:00 to 28-NOV-11 08:00:00 (CST-6)
Property damage: 0.00K
Reported by: Mesonet

Temperatures fell below freezing in wind protected areas of western Willacy County after midnight on the 28th, bottoming out in the mid 20s in these areas, and around freezing in rural locations with less wind protection.  The primary time for continuous subfreezing temperatures was between 4 and 8 AM, though some pockets fell to freezing as early as 2 to 230 AM.
Low temperatures included 24 degrees at the Lower Rio Grande Valley Wildlife Refuge site Linn/San Manuel (along the Willacy County line near SR 186), 31 degrees at the Climate Reference Network site along SR 186 near San Manuel, and 32 degrees at the Raymondville cooperative site.
Agricultural damage was unknown as of early December.  However, the dry freeze and associated low wet bulb temperatures, which ranged from the upper 20s to 31 degrees even in areas where air temperatures were a few degrees above freezing, likely caused minor problems to cold sensitive crops, particularly tender tropical vegetation.  The freeze reinforced the impacts from the intense drought (Extreme to Exceptional for most of the county).

Frost/Freeze in BROOKS, TEXAS
From 28-NOV-11 03:30:00 to 28-NOV-11 08:00:00 (CST-6)
Property damage: 0.00K
Reported by: COOP Observer

Temperatures fell below freezing in wind protected areas, including Falfurrias, between 3 and 4 AM and continued until 8 AM on the 28th.  Minimum temperature at the Hollywood Hunting Camp, 3.5 miles west of Falfurrias, dipped to 26 degrees between 7 and 8 AM.  Temperatures in non wind protected areas only fell into the mid 30s, including Brooks County Airport (2 miles southeast of Falfurrias).

Frost/Freeze in STARR, TEXAS
From 28-NOV-11 03:00:00 to 28-NOV-11 08:00:00 (CST-6)
Property damage: 0.00K
Reported by: Mesonet

Temperatures fell below freezing in wind protected areas of Starr County after midnight on the 28th, bottoming out in the mid to upper 20s.  Non protected or higher ground locations remained at or above freezing. At the Remote Automated Weather Station at Falcon Lake (just south of the Zapata/Starr County line), temperatures flirted with 32 degrees between midnight and 2 AM, and fell below 32 by 330 AM, reaching a minimum of 25 degrees just after 7 AM.  The cooperative station at Falcon Dam stayed just above freezing, while Rio Grande City reached 30 degrees between 7 and 8 AM.

Frost/Freeze in KENEDY, TEXAS
From 28-NOV-11 03:00:00 to 28-NOV-11 08:00:00 (CST-6)
Property damage: 0.00K
Reported by: Mesonet

Temperatures fell below freezing in wind protected areas of Kenedy County after midnight on the 28th, bottoming out in the mid 20s around daybreak.  The cooperative sites at Sarita (Lebh Shomeah retreat, 7 miles east) and Armstrong (on the King Ranch) each dipped to 25 degrees between 7 and 8 AM.

Frost/Freeze in ZAPATA, TEXAS
From 28-NOV-11 03:30:00 to 28-NOV-11 08:00:00 (CST-6)
Property damage: 0.00K
Reported by: COOP Observer

Temperatures fell below freezing in wind protected areas, including the Zapata County Airport (near Medina, northeast of Zapata), shortly after 5 AM and continued until 8 AM on the 28th.  Minimum temperature at the airport was 27 degrees. A Remote Automated Weather Station at Falcon Lake, just south of the Zapata/Starr County line, dipped to 25 degrees; temperatures reached freezing as early as midnight.

Frost/Freeze in JIM HOGG, TEXAS
From 28-NOV-11 04:00:00 to 28-NOV-11 08:00:00 (CST-6)
Property damage: 0.00K
Reported by: COOP Observer

Temperatures fell below freezing in wind protected areas, including Hebbronville, between 3 and 4 AM and continued until 8 AM on the 28th.  Minimum temperature at the Hebbronville Executive Inn (cooperative site) on the north side of town, dipped to 29 degrees between 7 and 8 AM.  Temperatures in non wind protected areas only fell into the mid 30s or higher, including Jim Hogg County Airport (4.5 miles northwest).