A blast of very cold Canadian air came sweeping down the Great Plains, migrating from the Yukon and Northwest Territories through Saskatchewan and Alberta Provinces, starting on January 6th. The high pressure cell, sourced near the Arctic Circle, brought sharply falling temperatures on January 7th, which would fall just below freezing across the Rio Grande Plains by daybreak of January 8th, and near freezing by mid to late morning on the 8th before struggling to rise into the mid 30s to near 40 toward evening under slate gray clouds, accompanied by a little sleet and rain mixed across the Lower Rio Grande Valley around midday.
Evening clouds on the 8th allowed a gradual temperature fall, but as skies cleared toward midnight, temperatures began a steady drop beginning across the Rio Grande Plains before midnight, spreading southeast and clearing the coast a couple of hours after midnight. By daybreak, all of Deep South Texas, save for the immediate coast and urban/developed locations, sustained hard freeze conditions.
Minimum temperatures ranged from the upper teens across the ranchlands of the Upper Rio Grande Valley of Zapata and Starr County stretching east through much of Jim Hogg, Brooks, northern Hidalgo, and into western Kenedy County.  Elsewhere, lows ranged through the low and mid 20s, except mid and upper 20s in the urban pockets of McAllen/Pharr/Edinburg and toward the immediate coast from Brownsville to South Padre Island, who even touched 32.
The freeze on the 9th probably caused the most damage for the entire period, as insulating frost was confined to low lying, wind protected areas.  Light winds and low humidity in most areas kept frost from developing.

Frost/Freeze in STARR, TEXAS
From 08-JAN-10 22:30:00 to 09-JAN-10 08:30:00 (CST-6)
Reported by: Mesonet

Temperatures fell below freezing during the late evening of the 8th, and ultimately fell to the lower 20s for most of Starr County by daybreak.  Coldest temperatures were found near ground level in low lying areas, including 18 at the Falcon Lake remote automated weather station location, and 21 at Rio Grande City. Freezing temperatures likely lasted up to 10 hours, with a hard freeze, defined as temperatures below 28 degrees, estimated to have lasted 4 to 8 hours in rural, low lying areas, and 3 to 6 hours elsewhere, generally between 2 and 8 AM.
Crop damage was unknown as of this writing.  Information from the Farm Services Agency of Starr County suggested some crop and grassland damage, but no reports were available as of this writing.
Sugar cane damage estimates will be available later in the spring of 2010.

Frost/Freeze in ZAPATA, TEXAS
From 08-JAN-10 06:00:00 to 08-JAN-10 10:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Despite abundant mid level cloudiness, shallow modified arctic air was able to reach into northern Zapata County before daybreak on the 8th, and continue through just before noon before temperatures rose a little above 32 degrees.

Frost/Freeze in KENEDY, TEXAS
From 08-JAN-10 22:15:00 to 09-JAN-10 09:15:00 (CST-6)
Reported by: AWOS

Temperatures fell below freezing during the mid to late evening on the 8th, and ultimately fell into the lower 20s by daybreak on the 9th across much of the King Ranch.  Low lying pockets dropped into the upper teens, including Armstrong. Freezing temperatures lasted up to 11 hours, with a hard freeze, defined as temperatures below 28 degrees, estimated to last 4 to 7 hours, longest in sheltered, wind protected areas.
Early planting of rangeland known as coastal grasses was severely damaged from the Freezes on the 9th and 10th in Brooks County, and similar damage may have been observed in Kenedy County.  Damage to these grasses, as well as any local tender vegetation, was unknown as of this writing.

Frost/Freeze in JIM HOGG, TEXAS
From 08-JAN-10 03:00:00 to 08-JAN-10 10:30:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Despite abundant mid level cloudiness, shallow modified arctic air was able to reach into northern Jim Hogg County before daybreak on the 8th, and continue through just before noon before temperatures rose a little above 32 degrees. Low temperatures at Hebbronville reached 30 degrees between 8 and 930 AM.

Frost/Freeze in JIM HOGG, TEXAS
From 08-JAN-10 20:00:00 to 09-JAN-10 09:30:00 (CST-6)
Reported by: AWOS

Temperatures fell below freezing during the mid evening of the 8th, and ultimately fell into the lower 20s across much of Jim Hogg County for more than 5 hours between 2 and 8 AM on the 9th.  Freezing conditions lasted for 13 and a half hours; a hard freeze, defined as temperatures below 28 degrees, lasted up to 9 hours.  Low temperatures reached 24 at Hebbronville Airport, but 19 at the cooperative location in town, where the sensor is at eye level and less affected by mixing winds.
Damage to grazing land was unknown as of this writing.

Frost/Freeze in COASTAL CAMERON, TEXAS
From 09-JAN-10 01:00:00 to 09-JAN-10 08:30:00 (CST-6)
Reported by: ASOS

Temperatures fell below freezing by 1 AM on the 9th, bottoming out in the upper 20s to around 30 by daybreak across Coastal Cameron County.  Lows ranged from 28 at Laguna Atascosa National Wildlife Refuge to 32 on South Padre Island. Freezing temperatures likely lasted up to 7 and one half hours.  A few pockets may have received an hour or two of a hard freeze, defined as temperatures below 28 degrees.
Crop damage was unknown as of this writing.  Information from the Farm Services Agency of Cameron County suggested only minor damage to citrus plants, with most fruit and trees surviving the freeze.  Tropical tender vegetation did not fare as well, but significant damage was not reported near the coast.

Frost/Freeze in ZAPATA, TEXAS
From 08-JAN-10 20:00:00 to 09-JAN-10 09:00:00 (CST-6)
Reported by: AWOS

Temperatures fell below freezing during the mid evening of the 8th, and ultimately fell into the lower 20s across much of Zapata County for more than 6 hours between 2 and 9 AM on the 9th.  Low lying areas in central and southern Zapata County dropped into the upper teens, with the Zapata airport in Medina hitting 19 degrees.  Freezing conditions lasted for 13 and a half hours; a hard freeze, defined as temperatures below 28 degrees, lasted up to 9 hours.
Damage to grazing land, as well as any local tender vegetation near the river, was unknown as of this writing.

Frost/Freeze in HIDALGO, TEXAS
From 08-JAN-10 23:00:00 to 09-JAN-10 09:00:00 (CST-6)
Reported by: Mesonet

Temperatures fell below freezing by late evening on the 8th, and bottomed out between 20 and 25 across most of Hidalgo County.  Coldest locations, with sensors at eye level, recorded lows of 19 degrees.  These included both Lower Rio Grande Valley National Wildlife Refuge locations near Linn/San Manuel (north portion of the county) and Santa Ana (along the Rio Grande just east of Pharr).  Other low temperatures include 22 at McCook, 25 at Edinburg, 26 at Weslaco, and 29 at McAllen's Miller Airport.
Freezing temperatures likely lasted up to 10 hours, with a hard freeze, defined as temperatures below 28 degrees, estimated between 4 to 8 hours in rural, low lying areas and 2 to 4 hours elsewhere, generally between 2 and 8 AM.
Crop damage was unknown as of this writing.  Information from the Farm Services Agency of Hidalgo County suggested minor damage to citrus plants and fruit, with most fruit and trees surviving the freeze.  Tropical tender vegetation did not fare as well, and there was substantial damage to sugar cane crops.
Sugar damage estimates will be available later in the spring of 2010.

Frost/Freeze in BROOKS, TEXAS
From 08-JAN-10 23:15:00 to 09-JAN-10 09:15:00 (CST-6)
Reported by: AWOS

Temperatures fell below freezing shortly before midnight on the 8th, and ultimately fell into the lower and mid 20s by daybreak on the 9th across much of Brooks County.  Freezing temperatures lasted up to 10 hours near Falfurrias and in locally colder pockets elsewhere, with a hard freeze, defined as temperatures below 28 degrees, lasting between 4 and 8 hours, with the longest duration in aforementioned colder pockets.  The cooperative station at the Hollywood Hunting Camp near Falfurrias dipped to 20 degrees; Brooks County Airport dropped to 24.
Early planting of rangeland known as coastal grasses was severely damaged from the Freezes on the 9th and 10th.  Damage to these grasses, as well as any local tender vegetation, was unknown as of this writing.

Frost/Freeze in CAMERON, TEXAS
From 09-JAN-10 00:00:00 to 09-JAN-10 09:00:00 (CST-6)
Reported by: ASOS

Temperatures fell below freezing around or shortly after midnight on the 9th, and ultimately fell into the 20s by daybreak across inland Cameron County.  A record low was set at Harlingen/Valley International Airport when the low fell to 25 degrees.  Elsewhere, readings ranged from 26 at the Harlingen Cooperative station just west of the Airport, to 29 in Brownsville and 28 in Mercedes. Freezing temperatures likely lasted up to 9 hours, with a hard freeze, defined as temperatures below 28 degrees, estimated to last 3 to 6 hours, longest in sheltered, wind protected areas.
Crop damage was unknown as of this writing.  Information from the Farm Services Agency of Cameron County suggested only minor damage to citrus plants, with most fruit and trees surviving the freeze.  Tropical tender vegetation did not fare as well, and there was substantial damage to sugar cane crops in the southwestern portion of the county.
Sugar damage estimates will be available later in the spring of 2010.

Frost/Freeze in COASTAL WILLACY, TEXAS
From 09-JAN-10 01:15:00 to 09-JAN-10 09:15:00 (CST-6)
Reported by: AWOS

Temperatures fell below freezing around or shortly after midnight on the 9th, and ultimately fell into the mid or upper 20s by daybreak across coastal Willacy County.  Port Mansfield fell to 26 shortly after daybreak; similar or slightly cooler readings were likely immediately west, and closer to 32 degrees right at the coast line.  Freezing temperatures likely lasted up to 8 hours, with a hard freeze, defined as temperatures below 28 degrees, estimated to last 2 to 4 hours, longest in sheltered, wind protected areas.
Crop damage was unknown as of this writing, but information from surrounding areas with similar planting suggest minor damage to dry land crops and more significant damage to tropical, temperature-sensitive plants.

Frost/Freeze in WILLACY, TEXAS
From 08-JAN-10 23:15:00 to 09-JAN-10 09:15:00 (CST-6)
Reported by: AWOS

Temperatures fell below freezing during the mid to late evening on the 8th, and ultimately fell to between 20 and 25 by daybreak on the 9th across inland Willacy County.  Raymondville fell to 21 shortly after daybreak.  Freezing temperatures likely lasted up to 10 hours, with a hard freeze, defined as temperatures below 28 degrees, estimated to last 3 to 6 hours, longest in sheltered, wind protected areas.
Crop damage was unknown as of this writing, but information from surrounding areas with similar planting suggest minor damage to dry land crops and more significant damage to tropical, temperature-sensitive plants.