Too Much Snow!!!....?

The Wasatch Front has been POUNDED with snow this week!!! Well, that is if you are comparing things with last year. While last year was much dryer than normal, much of Utah's snow totals so far this year are still below average despite "so much" new snow. Mother Nature hasn't been too friendly this January giving us extremely cold temperatures associated with a polluted inversion and then dumping us with three days of snow. Here's a question for you, would you rather live in a cold, dirty inversion or drive in the snow? I would much rather have the snow. I can ski in snow. What ever you think, don't get too sick of the snow yet: we still need more.

My thermodynamics professor loves the snow, too. He spend most of his research studying the stuff that fall from the sky. At Alta Ski Resort he installed a camera to take pictures of snowflakes in free-fall. The following are a few pictures his camera has captured:

The following link includes the most recent snowflake pictures. If it is snowing at Alta new pictures will load up automatically. Enjoy! http://www.alta.com/pages/snowflakeshowcase.php

(Mobile ozone and temperature sensor: photo (c) BKB)

I am involved in a research project at the University of Utah studying ozone formation in the Uintah River Basin, near Roosevelt and Vernal, Utah. This is a picture of a device I helped build. On top is a temperature and humidity sensor. An ozone sensor is also attached. A driver can drive around the basin taking measurements while a GPS keeps track of the position the measurement was taken. Kind of a cool set up.

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! ;)

Freezing Rain

On January 24, 2013, Salt Lake, Utah, Davis, Weber, and other counties in Northern Utah experienced freezing rain. Even a tenth of an inch of rain caused many problems. People had trouble walking to their car, let alone driving their car. Over 200 accidents were reported.

The following figure shows the basic meteorology at play when freezing rain occurs. We don’t usually get freezing rain in Utah because it requires cold surface temperatures and a warm, moist air mass above. Inversions, where the air near the ground is cold, is common in Utah. We don’t, however, experience warm winter storms very often. 

All month we have had a strong, shallow inversion in the valleys keeping the surface temperature in some places ten degrees below freezing or more. The other ingredient was also present. A warm, moist storm blew in from the southwest providing the precipitation. 

It is also worth noting that this storm did not clean out the polluted valleys. Because hot air floats on top of cold air, the air mass didn't dig into the valleys to replace the dirty air. All counties in northern Utah continued to have “Red” air quality days.

The next diagram is called a “skew-T.” This is the data collected from weather balloon launched from Salt Lake City Airport at 5:00 AM on the morning we woke up to freezing rain.

There are two black squiggly lines drawn up the graph. The right side black squiggly line represents the temperature for given heights. I drew in the sideways blue line to represent freezing temperatures. When the black temperature line is to the left of the freezing line, it is below freezing. When the black line is to the right of the freezing line, the temperature is above freezing. The blue and red highlighted part of the graph helps you see where temperatures are above or below freezing. A mountain is also depicted on the left to illustrate how tall the mountains are.

Warm air mass clouds can be made of ice crystals. The snow that falls from these clouds melt as it falls when temperatures are above freezing (the red highlighted area). The snow turns to rain. Near the ground is a shallow freezing layer. This is due to the temperature inversion caused by lack of solar heating in the day and losing radiation at night.

In this cold layer, you might wonder why it doesn't turn to hail. When water freezes it needs something to freeze onto. It has a hard time freezing to itself. Because the cold layer near the surface is thin, water doesn't freeze into hail. It becomes supercooled, meaning the liquid water is below freezing.

The instant a supercooled water droplet hits anything with a freezing temperature, such as a road, tree, or powerline, it will freeze to the surface creating an ice glaze.