Pair of "Aces" Sets Records
Heat spike pushes temperatures past 100°F March 14–15 2008

As expected, a spike of unseasonably hot and dry air covered much of the Rio Grande Valley and Deep South Texas on March 14th and 15th, courtesy of initially dry west to southwest winds flowing downwind of the higher terrain of northern Mexico and southwest Texas, all courtesy of a developing upper level ridge of high pressure in the central and western Gulf of Mexico. The mixing of dry air from higher levels of the atmosphere to lower levels almost always results in significant warming as the air descends. Meteorologically, we call this process "compression", since direct transfer of heat does not occur; rather, the "heat" is generated by the acceleration of gravity as the air mixes toward the surface. On March 14th and 15th, it was estimated that 15 to 17°C (roughly 30 to 33°F) of warming occurred between 5000 feet and the surface. Given measured and estimated 5000 foot temperatures between 23 to 25°C (roughly 73 to 77°F), resulting in afternoon high temperatures between 100 and 105°F generally from Hidalgo and western Brooks County west to Zapata, Starr, and Jim Hogg Counties.

On the 14th, southerly flow in the lower levels helped set up a dry line of much lower humidity from much higher humidity, and heat index, toward the Gulf (Figure 1, right). Temperatures within about 15 miles of the coast were much lower than those farther west; for example, Brownsville only reached 89°F while Harlingen rose to 95°F, and Raymondville even higher, to 101°F.

On the 15th, weak high pressure built into the region from the northwest, leaving surface winds light westerly to northerly through early afternoon, before turning northeast as the high scooted toward the lower Mississippi Valley. At the same time, measured temperatures at around 5000 feet at 7 AM CDT indicated 25°C. Without the hindrance of Gulf-influenced southeast flow to begin the day, even coastal locations were able to soar to near 100 degrees, before northeast winds took values down a bit by late afternoon. Tables 1 and 2 below show high temperatures and and new, standing, or former records, for March 14th and 15th.

As of this writing, virtually every observing location in the lower Rio Grande Valley broke a high temperature record on March 15th!

NWS Brownsville Doppler radar, 609 PM CDT March 14th, showing dry line east of McAllen (click to enlarge)
Figure 1. Doppler radar depicted dryline (boxed area) just after 6 PM CDT Friday, 3/14/2008.

Table 1. High temperatures (column 2), previous record/year (columns 3 and 4), and new record (yes or no, column 5), 3/14/2008.
City
High
Pvs Rec
Year
New?
McCook
105
102
1971
Y
McAllen/Miller
104
101
1971
Y
Falfurrias
104
100
1971
Y
Falcon Dam
104
101
2002
Y
McAllen/Co-op
103
100
1971
Y
La Joya
103
96
2002
Y
Zapata
102
100
1982
Y
Rio Grande City
102
106
1902
N
Hebbronville
102
98
1971
Y
Raymondville
101
101
1971
Tie
Sarita
101
87
2002
Y
Weslaco 2E
99
98
1971
Y
Mercedes
98
93
1928
Y
Harlingen
96
95
1928
Y
Brownsville
89
93
1971
N
Port Isabel
88
86
2001
Y
**Table 2. High temperatures (column 2), previous record/year (columns 3 and 4), and new record (yes or no, column 5), 3/15/2008.
City
High
Pvs Rec
Year
New?
Rio Grande City
104
102
2002
Y
McAllen/Miller
103
98
2002
Y
McCook
103
99
1911
Y
La Joya
103
100
2002
Y
Zapata
102
100
2002
Y
Harlingen
100
98
2002
Y
Hebbronville
100
97
2002
Y
Edinburg
100
97
2002
Y
Raymondville
100
99
1946
Y
Falfurrias
100
100
1945
Tie
Weslaco 2E
99
97
1961
Y
Brownsville
98
95
1902
Y
Mercedes
98
94
1945
Y
Port Isabel
89
86
2001
Y
Port Mansfield
88
84
2002
Y
** Preliminary Data as of 530 PM CDT March 15th, 2008
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