Saturday, May 23, 2020

Yesterday's Haboob

At around 1700-1800 MDT yesterday afternoon, a brief but violent dust storm or haboob swept through the Salt Lake Valley, degrading air quality and uprooting trees.

As described in the Glossary of Meteorology, the term haboob was first used to describe sand and dust storms in Sudan.  It is now commonly used to describe such storms in arid and semiarid regions around the world.  It is often used for dust storms in the American southwest, especially Arizona.  Below is an example from storm chaser Reed Timmer.

While there are many types of dust storms, haboob is typically applied to those with sharp leading edges caused by a density current or front.  It is often clear ahead of the density current, with opaque dust loading behind it.  

I first noticed yesterday's haboob at about 1730 MDT when it had spread into the northwest Salt Lake Valley.  Looking toward the southwest at that time, a shallow layer of dust was evident at low levels and clearly confined to elevations below the crest of the Oquirrh Mountains.  

At that time, strong northwesterly flow was observed in the northwest valley as high as 40 knots at the Kennecott tailings pile just south of I-80 and as high as 25 knots at the Trans Jordan Landfill in the southwest valley near the base of Kennecott's open-pit mine (labeled Bingham Canyon Mine on the plot below).  

Source: Mesowest
Time series from the tailings pile show steady northwesterly to northerly flow if 5-10 knots from approximately 1000 MDT to 1500 MDT.  From 1500-1700 MDT, that flow strengthened and the temperature fell about 4˚F.  At about 1700 MDT, the haboob hit, with sustained winds increasing rapidly to 50 mph and gusts reaching over 60 mph.  The temperature also fell more dramatically.

Source: MesoWest
Another perspective is provided below from the Neil Armstrong Academy just a bit further east and where there is a particulate matter sampler.  Here, one can see the Haboob passage isn't quite as abrupt, but still led to a peak in wind gusts to about 26 mph and apike in PM2.5 to 60 ug/m3, which is in the unhealthy for sensitive groups category, but not exceptional for such storms in Utah.  I've seen worse for sure.  

Source: Mesowest
A curious aspect of the Haboob is that it spread southward in the western Salt Lake Valley and then eastward across the southern Salt Lake Valley while the northeastern Salt Lake Valley around the University of Utah remained temporarily clear.  Below is a photo looking south through the Salt Lake Valley showing the dust blanketing the southern Salt Lake Valley.

And below is a video showing the haboob surging across the southern Salt Lake Valley.

And, given Blogger's inability to adequately process video in some instances, here's a still.

Source: University of Utah
Eventually dust came into the northeast Salt Lake Valley from the west.  I'm not sure why we were temporarily spared, but here are a couple of possibilities.  One is that the dust source, which may have been Salt Lake Playa, was such that the northeast Salt Lake Valley simply wasn't immediately downstream for northwest flow.  The other is that the haboob density current was blocked initially by the transverse mountains that extend westward between the northeast Salt Lake Valley and Bountiful (i.e., the terrain surrounding City Creek Canyon, including the Avenues Foothills).  Some evidence is provided below for 1800 MDT which shows weaker winds in the northeast Salt Lake Valley.  

Source: Mesowest
Further analysis is needed to evaluate those hypotheses.

Further analysis is also needed to evaluate the origins of the haboob, but the analysis below shows that it wasn't a microburst.  Strong northwesterly flow is evident from the west Desert to the Wasatch Front. 

Source: Mesowest
Thus, this was a fairly large-scale feature, possibly enhanced by cooling beneath the frontal precipitation band that lagged the wind shift.  

There were reports of wind damage with the haboob, such as the downed trees below in the Avenues.
I also noticed a report of downed power lines in West Jordan.

This morning we awake to a different scene with much colder temperatures and snow blanketed mountains.  What a relief to have rain!  However, if you don't like this weather, check out the NWS forecast below.  Climbing temperatures all week and a forecast high of 94 on Friday!

Source: NWS

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