Meteorological aspects of the 2006 El Paso Texas metropolitan area floods

The summer monsoon of 2006 was historically wet across far western Texas, south central and southwestern New Mexico. Numerous mesoscale convective systems produced excessive rainfall with attendant and at times destructive flash floods. Heavy rainfall and flooding were particularly severe over El Paso, Texas and adjacent communities where flood damage estimates approached $450 million. The occasionally torrential rains around this area fell between 27 July and 4 August, and were particularly heavy during the morning and early afternoon of 1 August when 3 to 10 inches (75 to 250 mm) of rain fell. This resulted in flooding which severely damaged portions of the region and forced the Rio Grande to overflow as the river reached its highest level since 1912. The series of convective storms occurred in an environment which included unusually high and deep moisture content, weak to moderate instability, and minimal convective inhibition. Light wind speeds with little vertical wind shear through the cloud layer resulted in slow-moving or upstream-propagating cells. Storm initiation and sustenance over the nine day period was due to a combination of several middle-tropospheric troughs (including a convectively enhanced vortex), sustained upslope wind flow over high terrain, and weak surface boundaries. Using buoyancy to derive updraft strength, theoretical sub-cloud moisture convergence, and cloud condensation rates, two techniques were explored to derive rainfall intensities for the 1 August convection. It was determined that for this event, theoretical sub-cloud moisture convergence values provided results consistent with observations. From a climatological perspective, the heavy rainfall episode greatly contributed to daily, monthly, and seasonal records for the El Paso metropolitan area, with the summer monsoon of 2006 becoming the wettest on record.