Friday, January 31, 2014

Weather Stations

In the environmental instrumentation class we set up weather stations and collected weather data for a week. Each weather station has a wind monitor to measure wind speed and direction, a temperature and relative humidity sensor, and a barometer to measure air pressure.

Monday, January 27, 2014

Weather Instruments

This semester I'm a TA for an environmental instrumentation class. In the class we program data loggers and test the performance of several types of weather sensors. Shown below is a wind monitor, temperature and humidity sensor, and a pressure sensor wired to a Campbell Scientific data logger. This week the class will set up weather stations and collect weather data for a week.

Frosted Trees

On cold, clear nights, frost will deposit on trees like dew. Here is a frosted tree at the University of Utah:

Wednesday, January 15, 2014

Measuring Groundwater from Satellites

The Utah Climate Center at the Utah State University publishes monthly climate notes. This month's issue has an article about measuring groundwater from satellites. "How in the world can you measure groundwater from a satellites", you might ask. I sure wondered how that is possible. You can read the article here. The basic idea is to have two satellites orbiting the earth fairly close together (about 120 miles apart from each other). As these two satellites communicate with each other, they measure the distance between each other which is related to the gravity of the earth. Despite what you learned in physics class, gravity is not constant. From small changes in the spacing of these two satellites a change in gravity can be calculated. Since all mass on earth contributes to the gravitational force, the absence or abundance of water underground will affect the gravity these satellites measure. Thus, groundwater levels can be measured by remote sensing. Kind of cool!  Again, you can read the entire article here:

Also in this issue is a chart showing the current winter snow pack for various locations in Utah. The bottom line is this: WE NEED MORE SNOWSTORMS!!!

Wednesday, January 8, 2014

Freezing Fog vs. normal Fog

This was an attempt to capture pictures of freezing fog. This evening (January 8, 2014) at my house it was 26 F with relative humidity at 91%. This is a recipe for freezing fog because temperatures are below freezing and the humidity is close to 100% meaning that the air is saturated with water vapor.

Below are the pictures I attempted to take to illustrate the difference. The top row shows pictures taken with out a flash, and the bottom show pictures taken with a flash. In the frozen fog, it is easy to see each individual crystal. In fact, sometimes the crystals grow too large and will fall out of the air to the ground. I created the normal, water drop fog by breathing heavily into the air. The warm, humid air I breathed condensed into water droplets like a cloud. Water droplet fog makes a much more dense looking cloud. It looks thicker because it is made of tiny water droplets which in turn scatters more light. Eventually the liquid water droplet fog I created with my breath froze and mixed with the rest of the frozen fog. Kind of cool!

Monday, January 6, 2014


A mass of cold, cold air from the polar region is pushing south into the central United States. Below is a map from MesoWest showing the Real-Time Mesoscale Analysis of the temperatures over the United States at about 21:30 GMT (2:30 PM Mountain Time). You can see the cold air extending into Illinois. Also, notice the temperatures over the Great Lakes, which haven't cooled off as fast. This is because water has a high specific heat.

The National Weather Service stations in the area are reporting temperatures as cold as -20 F (at 2:30 PM Mountain Time). That is bitter cold and very dangerous. I suppose I won't complain about my comfy 32 degrees.

Wednesday, January 1, 2014

Surface Hoar

Last weekend I did a quick trip to Arches National Park. The park is pretty in the winter with the snow covered red rocks, but I was surprised how many people were out hiking in the cold weather. Anyways, when we arrived at Delicate Arch, while everyone was gazing at the amazing arch, I was looking at the incredible surface hoar!

Surface hoar is found on the surface of snow after a cold night. It looks like this...
Photo by NGB

 It forms by vapor deposition, which is when water vapor (water in its gas phase) freezes, or deposits, to a snow surface. It makes these feathery like structures on the snow surface. It is most common after a cold, clear night in areas when the air is humid. It is especially common in areas with a water source like a river or stream. Light winds are also favorable to surface hoar formation because the light wind will re-supply the air right above the snow with more water vapor to condense on the surface.

Surface hoar can become an avalanche hazard when it is buried by a layer of new snow. It makes a slick, unstable layer which the new snow can slip easily on.