Sunday, January 27, 2013

Clean Air

(c) BKB
Finally, some clean air. We've been stuck in an inversion the last few weeks causing horrible pollution. The north half of Utah had the worst air quality in the nation for a week! Here is a picture of me in Big Cottonwood Canyon looking down on the valley inversion...

The time the cold front passed Salt Lake can be found by looking at the temperature change from the weather station at the Gateway Mall in Salt Lake City. The red line represents the temperature. Around 10:00 AM the temperature reached 44 degrees. But look at what happened quickly after...the temperature took a ten degree dive in about 30 minutes!
(image from Mesowest.utah.edu)
 You can also identify the passing cold front by looking at the wind directions. Before a cold front passes, winds will blow from the south. After the cold front passes winds come from the north and northwest. There is a definite change in wind direction at 10:00 AM.


(image from Mesowest.utah.edu)

The following image shows the PM 2.5 concentrations in the Salt Lake Valley. This graph is hard to read, but the back circles is what you want to look at. In the right third of the picture you can see the black circles getting lower. This means our air is getting cleaner! As this storm continues to push through we can expect the air quality to improve
(image from airquality.utah.gov)


This next graph shows Provo's air quality from the following week. Utah County's air quality has by far been the worse in Utah. With south winds increasing before the storm and movement of the storm through Utah County the air quality has improved and will continue to get better
(image from airquality.utah.gov)


So, as the storm first blew through Salt Lake, this is the stuff that fell...























(c) BKB

This isn't just normal snow. It is called graupel. Graupel looks kind of like hail, but it is formed differently. It looks and feels like foam pellets you might find in packaging material. It started as a common snowflake, but as it fell to the ground, it encountered supercooled water droplets which immediately froze to the snowflake. This is called rimming. This kind of stuff is usually perfect for making a snowball because it is relatively warm and wet snow.

It took a few more hours, but the cold front eventually reached Utah County also changing the wind direction from south to northwest, caused a 10 degree temperature drop, and brought graupel and snow. You better get the snow shovel ready for Monday morning! ;)

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