Clear skies and light winds allowed temperatures to fall steadily after sunrise from January 3rd highs in the lower 50s, and soon after midnight readings were at or below 32 across the ranchlands and wind-protected areas of the upper Rio Grande Valley.  Low temperatures bottomed out in the mid to upper 20s across most of the ranchlands, with slightly higher temperatures (still below 32) in non-wind-protected locations along Texas State Route 285. Frost was common in the Lower Valley and may well have occurred in wind protected colder locations elsewhere.

Frost/Freeze in BROOKS, TEXAS
From 04-JAN-18 01:00:00 to 04-JAN-18 08:30:00 (CST-6)
Reported by: AWOS

The AWOS at Falfurrias recorded a low temperature of 31 degrees.  However, wind protected ranchlands south and southwest likely fell into the mid and upper 20s, based on proxy observations from Kenedy, nothern Hidalgo, and western Willacy County. While frost was not recorded specifically, wind protected locations may have received some due to the clear, calm conditions that followed several days of cloudy and chilly conditions.

Frost/Freeze in CAMERON, TEXAS
From 04-JAN-18 06:00:00 to 04-JAN-18 08:00:00 (CST-6)
Reported by: ASOS

The ASOS at Brownsville/South Padre Island International Airport fell to 31 degrees early on the 4th, the coldest temperature recorded there since nearly a year ago (January 7, 2017, also 31 degrees).  Harlingen/Valley International Airport fell to 30 degrees, and a few locations may have touched into the upper 20s.  Light frost was fairly widespread across the county. Impact to agriculture from this particular day was unknown; multiple cold days in a row followed by another long-duration but minor freeze less than two weeks later may have aggregated the damage.

Frost/Freeze in STARR, TEXAS
From 04-JAN-18 01:00:00 to 04-JAN-18 08:00:00 (CST-6)
Reported by: COOP Observer

Minimum temperatures at Rio Grande City and Falcon Lake RAWS fell to 27 and 26 degrees respectively, the coldest since the same readings were recorded nearly a year earlier (January 8, 2017).  By proxy, much of Starr County likely fell to the upper 20s based on observations from Zapata to Jim Hogg and western Hidalgo County. Clear, calm  conditions aided the steady drop in temperatures after sunset on the 3rd.

Frost/Freeze in KENEDY, TEXAS
From 04-JAN-18 01:00:00 to 04-JAN-18 08:30:00 (CST-6)
Reported by: COOP Observer

The cooperative observer 7 miles east of Sarita recorded 23 degrees, their coldest temperatures since January 7 and 8 (26 and 27) 2017 under clear skies and calm winds. Other nearby observations included 26 in Kingsville and San Manuel (northeast Hidalgo), and 28 in Raymondville. Duration of subfreezing temperatures is estimated from proxy observations at the RAWS/Mesowest location in San Manuel, adjusted to include both wind and non-wind protected locations.

Frost/Freeze in WILLACY, TEXAS
From 04-JAN-18 04:00:00 to 04-JAN-18 08:00:00 (CST-6)
Reported by: COOP Observer

The cooperative observer in Raymondville recorded a low temperature of 28 degrees.  Temperatures across the county were likely in the upper 20s, based on proxy observations at Linn/San Manuel RAWS (26) and Harlingen/Valley Int'l Airport ASOS (30). Duration of event was a blend between the colder ranching communities and slightly warmer farming communities closer to the more populated Lower Valley.

Frost/Freeze in COASTAL WILLACY, TEXAS
From 04-JAN-18 06:00:00 to 04-JAN-18 08:00:00 (CST-6)
Reported by: COOP Observer

The cooperative observer in Port Mansfield recorded a low temperature of 32 degrees under clear and mainly calm conditions.  Temperatures in other nearby locations may have fallen a degree or two lower based on an observation from the RAWS/Mesowest site at Laguna Atascosa National Wildlife Refuge in northeast Cameron County.

Frost/Freeze in COASTAL CAMERON, TEXAS
From 04-JAN-18 06:00:00 to 04-JAN-18 08:00:00 (CST-6)
Reported by: RAWS

The RAWS/Mesowest location at Laguna Atascosa National Wildlife Refuge fell to 29 degrees, and Bayview/Cameron County Airport fell to 31 degrees, under clear and calm conditions early on January 4th. cooperative observer in Port Mansfield recorded a low temperature of 32 degrees under clear and mainly calm conditions.  These were the coldest temperatures along the Lower Texas coast since January 7, 2017 - nearly one year earlier.

Frost/Freeze in HIDALGO, TEXAS
From 04-JAN-18 04:00:00 to 04-JAN-18 08:00:00 (CST-6)
Reported by: RAWS

Most of Hidalgo County fell to or below freezing early on January 4th, with the sole exception of the City of McAllen. Across the ranch and farming communities north of the populated areas, temperatures fell into the mid and upper 20s, as did wind-protected Santa Ana National Wildlife Refuge on the Rio Grande near Pharr (23 degrees). Weslaco and Edinburg fell to 32.  In general for the county, about 4 hours of freezing temperatures were observed under clear and calm conditions.

Frost/Freeze in ZAPATA, TEXAS
From 04-JAN-18 01:15:00 to 04-JAN-18 08:35:00 (CST-6)
Reported by: COOP Observer

Minimum temperatures at Zapata County Airport fell to 26 degrees, as did the low at Falcon Lake RAWS, just inside Starr County south of the Zapata/Starr County line. Based on observations in Starr County, low temperatures likely fell into the mid and upper 20s county-wide under clear and calm conditions.

Frost/Freeze in JIM HOGG, TEXAS
From 04-JAN-18 01:15:00 to 04-JAN-18 08:35:00 (CST-6)
Reported by: AWOS

Minimum temperatures at Jim Hogg County Airport 4 miles northwest of Hebbronville reached 30 degrees early on January 4th, but a pocket of mid to upper 20s temperatures likely was observed across most ranch areas based on proxy observations in Hidalgo, Starr, and Zapata County. Clear, calm conditions led to the coldest readings since January 8, 2017.