A Brief But Intense Lake-Dust Event

Late yesterday afternoon, strong winds associated with outflows from storms to the north brought a brief but intense lake-dust event to the Salt Lake Valley.  Satellite imagery showed this dust moving southward through the Salt Lake and Utah Valleys.

Source: CIRA.  Loop also available at https://col.st/80KK0. 

Take a close look at that look, especially the last few frames, and you can also see an area of dust moving off of the Farmington Bay playa and over the south arm of the Great Salt Lake.  There's also evidence of dust from other sources to the west moving through the Skull, Tooele, and Rush Valleys.

Winds at the University of Utah began to pick up at around 1835 MDT when increased to more than 9 mph with gusts to 12 mph.  The peak gust of 20 mph occurred at 1852.  This roughly bracketed a spike in PM2.5 concentrations to just over 8 ug/m3 from 1845-1850 UTC. 

Source: Mesowest

Although the PM2.5 concentrations were not very high, that measurement focuses on smaller particles less than 2.5 microns, whereas wind-blown dust from the lake often contains larger particles and is better measured by instruments that focus on particles up to 10 microns (called PM10).   

Events yesterdays are typical of most July-August dust storms.  They tend to be intense but shortlived and generated by precipitation falling into sub-cloud dry layers, which leads to evaporative cooling.  The evaporatively cooled air spreads outward from the precipitation region, often resulting in strong winds.  The leading edge of this outflow is sometimes referred to as an outflow boundary or gust front.  Often you can see several, which can merge and interact, as evident in yesterday's satellite loop. 

If the lake was full, dust would have been more limited.  Some of us might have only felt a cool and refreshing north wind.  Wouldn't that have been wonderful.