Century Mark (Fahrenheit) temperatures set RGV records on March 14 and 15 2008

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