Average snow depth from three acoustic sensors is now available on the NWS Milwaukee/Sullivan weather observation page. Below is some background and specifics about these sensors.
In 2006 the NWS Milwaukee office became one of 14 offices across the country selected in a study to test the accuracy of automated snow sensors. The study conducted in conjunction with Colorado State University was intended to find a more accurate and efficient means of measuring snow depth. This study found that the instruments proved to be fairly accurate. In addition, it was determined at the NWS Milwaukee/Sullivan office that the snow sensors performed well in comparison to human measurements made by our forecasters through two seasons of testing. Below is an image of the sensors:
Acoustic sensors send a pulse from the instrument straight downward. A snowboard is located at the ground below the sensor. The sensor records the amount of time for the pulse to bounce back off of the surface of the snowboard or top of the snow cover. This result is then calculated into a distance between the height of the sensor and the height of snow. The shorter the time it takes for the pulse to return, the less distance between the snow and sensor, and thus the higher the snow depth.
5-minute snowfall observations are recorded by three snow sensors and then averaged. The last 24 hours of data is then plotted and updated on the web every 10 minutes.
Observation times are noted at the bottom of the graph in central time based on a 24 hour clock (0200 = 2 am, 1300 = 1 pm, etc.).
The data goes through some rough quality control steps, but should still be considered experimental and some noise may still appear particularly in low snow depth conditions, i.e., animals moving under the sensors or other objects blowing by could lead to erroneous data.
There may be times when a slight wave pattern is noted in the observations. This is most often due to settling of the snow pack, primarily in the middle of a snow event or shortly after, the weight of the snow will cause the collapse of small air pockets leading to slight settling. Also on windy days there could be some variations in the snow depth.