Wednesday, June 29, 2011

Dust Event Yesterday, post by Jeff

Dust became visible yesterday afternoon a little after 5pm in the salt lake valley and it stuck around for much of the evening. Here is an image from the Olympus cove weather cam

The event yesterday took place in the pre frontal environment of an approaching Intermountain Cyclone, which is very typical for spring time dust storms. The IDV analysis from 6pm yesterday clearly shows an area of low pressure over north-eastern Nevada riding along an anomalously strong pacific trough for this time of year.

One of the biggest issues Jim and I have faced researching Utah dust transport is determining when a dust event takes place. Dust observations require human input making them very subjective. Unfortunately yesterday was a perfect example of why you can not always rely on human observation. When the dust came through yesterday the visibility dropped to 4 miles, but KSLC reported haze even with a 10% relative humidity!

Dust detection from satellite can also be very tricky. Remote dust retrieval only works during the day and when there are no clouds present. MODIS has high resolution, but only passes over Utah once during the day. Yesterday the pass came around noon when there were only a few small plumes over the West Desert.
Luckily a more simplified dust retrieval algorithm can be applied to GOES data, which reports about every 15 minutes. At around 5pm the only real visible plume is over SW Nevada and UT is fairly quiet. The dust we saw here was either too weak or too late in the day to be picked up by the algorithm.

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