A section of modified arctic high pressure settled over Deep South Texas and the Rio Grande Valley late on February 4th into early February 5th, bringing clear skies, nearly calm winds, and the coldest air temperatures of the three day period to most areas.
After an ice storm departed all areas by midday on the 4th, sunshine returned, bringing temperatures above freezing but only into the 40s, except upper 30s along the coast.  With low relative humidity, the stage was set for rapid temperature falls during the evening of the 4th; before midnight, most locations away from the coast (where some wind continued) fell below 32F and would continue dropping steadily.  By daybreak on the 5th, hard freezes (temperatures below 28 for several hours) covered rural areas north and west of the Lower Rio Grande Valley; sheltered pockets fell into the teens.
Readings quickly rose above freezing by mid morning of the 5th, ending the freeze event - until the next one arrived just five days later.

Frost/Freeze in CAMERON, TEXAS
From 05-FEB-11 00:00:00 to 05-FEB-11 08:15:00 (CST-6)
Property damage: 0.00K
Reported by: ASOS

For Cameron County, air temperatures likely fell to 32F between 11 PM February 4th and 1 AM  February 5th, and continued falling into the upper 20s to around 30F, on average, before sunrise, with these temperatures continuing until an hour or so after sunrise before rapidly rising into the 50s by noon.  A hard freeze - temperatures below 28 degrees for 2 or more hours - likely occurred in a few pockets north and west of Harlingen and Brownsville.
Selected low temperatures included Brownsville/South Padre Island Int'l Airport (31 degrees; 5 hours of freezing), Harlingen/Valley Int'l Airport (28 degrees, 5 hours of freezing), Harlingen Cooperative (27 degrees), and Santa Rosa (29 degrees).
Additional light to moderate damage to cold sensitive crops likely occurred with the cold temperatures on the 5th.  See the report for the long duration freeze from the 3rd through the 4th for details.

Frost/Freeze in KENEDY, TEXAS
From 04-FEB-11 20:00:00 to 05-FEB-11 08:30:00 (CST-6)
Property damage: 0.00K
Reported by: COOP Observer

Temperatures dipped to 32F as early as 8 PM on February 4th, and would continue through 830 AM on the 5th before quickly rising into the 40s and 50s before noon.  A hard freeze - temperatures below 28F for 2 hours or more - was widespread across the King Ranch. The low at cooperative sites in Armstrong (south Central portion) was 21 degrees, and at the Lebh Shomea House of Prayer (7 miles east of Sarita) dipped to 23 degrees.
The hard freeze, which lasted an estimated 5 to 10 hours, further contributed to freeze drying of grasses and scrub brush on the King Ranch.

Frost/Freeze in STARR, TEXAS
From 04-FEB-11 20:00:00 to 05-FEB-11 08:45:00 (CST-6)
Property damage: 0.00K
Reported by: COOP Observer

Temperatures dipped to 32F as early as 8 PM on February 4th, and would continue through 830 AM on the 5th before quickly rising into the 40s and 50s before noon.  A hard freeze - temperatures below 28F for 2 hours or more - covered all of the county.
The low at the Falcon Lake Remote Automated Weather Station, just south of the Zapata/Starr County line, dipped to 16 degrees with a hard freeze for 12 hours. The cooperative observer at Falcon Dam, nearby, recorded a low of 25 degrees, which may have been influenced by warmer temperatures near Falcon Lake. The cooperative observer at Rio Grande City recorded a low of 21 degrees.

Frost/Freeze in JIM HOGG, TEXAS
From 04-FEB-11 19:30:00 to 05-FEB-11 08:30:00 (CST-6)
Property damage: 0.00K
Reported by: AWOS

Temperatures dipped to 32F as early as 730 PM on February 4th, and would continue through 830 AM on the 5th before quickly rising into the 40s and 50s before noon.  A hard freeze - temperatures below 28F for 2 hours or more - was widespread in the largely rural county. The low at Jim Hogg County Airport (northwest of Hebbronville) dipped to 27 degrees,  which held for 7 hours.   Interpolating between observing locations in Starr and Zapata County suggested up to 13.5 hours hours of freezing temperatures during the event in much of the county; lows in central and southern portions likely fell to 20F or below.

Frost/Freeze in COASTAL CAMERON, TEXAS
From 04-FEB-11 23:00:00 to 05-FEB-11 08:15:00 (CST-6)
Property damage: 0.00K
Reported by: ASOS

For coastal Cameron County, air temperatures likely fell to 32F by approximately 11 PM on February 4th (pockets fell to 32F as early as 915 PM), and continued falling into the upper 20s to around 30F, on average, before sunrise, with these temperatures continuing until an hour or so after sunrise before rapidly rising into the 50s by noon.  A hard freeze - temperatures below 28 degrees for 2 or more hours - occurred in a few pockets north and east of County Road 106, generally near the Laguna Atascosa National Wildife Refuge, where minimum temperature fell to 24 degrees with hard freeze conditions lasting up to 6 hours.
The long duration of cold was aided by highs on the 4th, which only reached 40, giving a head start to rapid cooling in light winds and starry skies. Other low temperatures included Bayview/Cameron County Airport (29 degrees; 7 hours of freezing) and South Padre Island heliport (29 degrees; 9 hours of freezing temperatures).

Frost/Freeze in BROOKS, TEXAS
From 04-FEB-11 20:00:00 to 05-FEB-11 08:30:00 (CST-6)
Property damage: 0.00K
Reported by: COOP Observer

Temperatures dipped to 32F as early as 8 PM on February 4th, and would continue through 830 AM on the 5th before quickly rising into the 40s and 50s before noon.  A hard freeze - temperatures below 28F for 2 hours or more - was widespread in the largely rural county. The low at Brooks County Airport (southeast of Falfurrias) dipped to 27 degrees,  which held fo 2.5 hours.  The cooperative observer at the Hollywood Hunting Camp (west of Falfurrias) recorded a low of 21 degrees.  Interpolating between observing locations at Linn/San Manuel suggested between 12 and 13 hours of freezing temperatures during the event in much of the county.

Frost/Freeze in WILLACY, TEXAS
From 04-FEB-11 23:00:00 to 05-FEB-11 08:15:00 (CST-6)
Property damage: 0.00K
Reported by: COOP Observer

For most of Willacy County, air temperatures fell to 32F by approximately 11 PM (sheltered locations likely fell to 32F by 8 PM), and continued falling into the mid and upper 20s, on average, before sunrise, with these temperatures continuing until an hour or so after sunrise before rapidly rising into the 50s by noon.  A hard freeze - temperatures below 28 degrees for 2 or more hours - was common for most of the largely rural county. Coldest temperatures in the mid 20s were most likely west of Raymondville, interpolated from 24 degrees at San Manuel (less than 10 miles west of the border).
Other specific temperatures included:  27 degrees at the Port Mansfield and Raymondville cooperative observing stations, and 24 degrees at Laguna Atascosa NWR (9 miles south of the county line).
Additional light to moderate damage to cold sensitive crops likely occurred with the cold temperatures on the 5th.  See the report for the long duration freeze from the 3rd through the 4th for details.

Frost/Freeze in HIDALGO, TEXAS
From 04-FEB-11 23:00:00 to 05-FEB-11 08:15:00 (CST-6)
Property damage: 0.00K
Reported by: ASOS

For all but urban centers of Hidalgo County, air temperatures fell to 32F by approximately 11 PM (sheltered locations likely fell to 32F by 8 PM), and continued falling into the mid and upper 20s, on average, before sunrise, with these temperatures continuing until an hour or so after sunrise before rapidly rising into the 50s by noon.  A hard freeze - temperatures below 28 degrees for 2 or more hours - was common for all but the Lower and Mid Valley communities from Mission to Weslaco, where temperatures grazed 27 degrees.  Ranchland across the northern third of the county (McCook and other locations) saw temperatures dip to near 20 degrees, by interpolation.
Specific temperatures included:  24 degrees at San Manuel (8 hours of hard freeze), 24 at the Santa Ana NWR near Pharr (7 hours of hard freeze), 26 at La Joya, 27 at McAllen/Miller Airport (<1 hour of hard freeze), and 29 degrees at Weslaco (5 hours of freezing).
Additional light to moderate damage to cold sensitive crops likely occurred with the cold temperatures on the 5th.  See the report for the long duration freeze from the 3rd through the 4th for details.

Frost/Freeze in COASTAL WILLACY, TEXAS
From 04-FEB-11 23:00:00 to 05-FEB-11 08:15:00 (CST-6)
Property damage: 0.00K
Reported by: COOP Observer

For coastal Willacy County, air temperatures likely fell to 32F by approximately 1 AM,  and continued falling into the upper 20s, on average, before sunrise, with these temperatures continuing until an hour or so after sunrise before rapidly rising into the 50s by noon.  A hard freeze - temperatures below 28 degrees for 2 or more hours - may have occurred a few miles inland from Port Mansfield.  The low temperature at Port Mansfield reached 27, likely during the pre dawn hours of the 5th and continuing for an hour or two either side of sunrise.

Frost/Freeze in ZAPATA, TEXAS
From 04-FEB-11 20:00:00 to 05-FEB-11 08:45:00 (CST-6)
Property damage: 0.00K
Reported by: AWOS

Temperatures dipped to 32F as early as 8 PM on February 4th, and would continue through 830 AM on the 5th before quickly rising into the 40s and 50s before noon.  A hard freeze - temperatures below 28F for 2 hours or more - covered all of the largely rural county. The low at Zapata County Airport (Medina) dipped to 18 degrees,  with a hard freeze holding for 12 hours.  The Falcon Lake Remote Automated Weather Station, just south of the Zapata/Starr County line, dipped to 16 degrees with a hard freeze for 12 hours.