I live in Phoenix, Arizona and we get some serious dust storms during our monsoon season (now called the Summer Thunderstorm Season according to meteorologists). We have those same 110 to 120 degree temps here too. Before I digress too much, here’s what Wikipedia wants us to know about dust storms:
A dust storm or sandstorm is a meteorological phenomenon common in arid and semi-arid regions and arises when a gust front passes or when the wind force exceeds the threshold value where loose sand and dust are removed from the dry surface. Particles are transported by saltation and suspension, causing soil erosion from one place and deposition in another.
As the force of wind passing over loosely held particles increases, particles of sand first start to vibrate, then to saltate (“leap”). As they repeatedly strike the ground, they loosen smaller particles of dust which then begin to travel in suspension. At wind speeds above that which causes the smallest to suspend, there will be a population of dust grains moving by a range of mechanisms: suspension, saltation and creep.
Unfortunately, I couldn’t find any information as to why dust storms seem to be more prevalent in summer months, such as July.