Dust events are categorized into two major types: 1) Synoptic Scale and 2) Mesoscale. The synoptic types are further broken down into two subtypes (based on the origin of their generating cold fronts: 1a) Pacific or 2a) Continental Polar (backdoor) fronts. Synoptic scale dust events are most frequent in the late winter and spring seasons (February through May) (64%) but also occur in the late fall and early winter seasons. Most result from Pacific upper level troughs and their associated surface cold fronts producing surface cyclogenesis over northern New Mexico which in turn tightens the surface pressure gradient producing strong gusty west to southwest winds across dry, exposed desert soils. This along with ample solar radiation permits sufficient dry convection which in turn vertically mixes the dust in planetary boundary layer and occasionally into the free troposphere where it may be transported long distances. Mesoscale type dust events are most prevalent in the summer season during the North American monsoon. These dust events are produced from strong thunderstorm outflows and microbursts and are generally less intense and more localized than the synoptic types, accounting for only 2.5% of all the dust events.
Data are presented showing the duration as well as the frequency of dust storms. Statistical information on the attendant meteorological parameters of wind speed, direction, visibility and relative humidity is also analyzed. The “classical” blowing dust events occur during the months of March and April and are most frequent in the mid afternoon hours lasting on the average around 3- 4 hours. The average wind speed is around 25-30 mph with gusts of 35-40 mph. The average relative humidity occurring during these dust events is fairly low at 18%. An analysis of annual precipitation and dust events is also presented showing a high correlation of increased dust storm activity during the years with below average precipitation. A noted increase in the number of dust storms (up by 34%) was observed in the ten year period from 1994-2003 under drought conditions during which El Paso received only 73% of its average rainfall. A significant portion of dust events in the 1930s was associated with backdoor cold fronts with east winds blowing in from the Dust Bowl region.
El Paso averages 14.5 significant dust events per year; their consequences range from simple irritations and increased particulate matter concentrations to serious disruptive events aggravating respiratory health problems and even can turn deadly in fatal collisions in near-zero visibility on city roadways and highways in the surrounding desert.
Common dust sources have been identified and show a distinct preference for dust events to originate in the playas (dry lake beds) of the Chihuahuan desert surrounding El Paso as well as in some local natural and anthropogenic sources in southern New Mexico and far west Texas.
A local forecast aid has been developed from this synoptic climatology study and shows a mean synoptic case in which all contributing meteorological parameters such as wind profiles, temperatures, etc. are optimized in phase to produce the typical blowing dust scenario experienced in El Paso, Texas.