How Snow Totals are Documented

After receiving our first snowfall of the winter there was one question many viewers were asking…why was the official total so low at 8.8″? The answer isn’t as complicated as you might think. There is no perfect way to get snow totals for one location. When looking at snow totals on a micro-scale they differ a ton. That is why the National Weather Service uses ASOS (Automated Service Observing Systems). These weather systems can collect data such as temperature, dew point, temperature, wind speeds, cloud conditions, rain totals, and snow totals to name a few. This information gets collected and then documented by the NWS.

Here is a map of all the ASOS stations across the nation:

natl_ASOS

The information from these sites are the most precise weather data meteorologist can collect. The data helps with research and climate data for that area. These systems aren’t effected by blowing/drifting snow when calculating accumulation totals.

This previous snow event can show how difficult forecasting snow events can be. All it takes is one little heavy snow band within a system to bust a forecast for a meteorologist and that occurred in some areas of the Stateline Friday and Saturday. Areas just northeast and west of the Rockford Metro experience those heavier snow bands and that’s what lead to amounts reaching over a foot of snow. The gradient between snow bands was very tight during this event and that’s why just six miles away from a specific location could have received 5-8 more inches of snow.

Due to these heavy snow bands within a system there will never be a measurement the same in all areas of a large city like Rockford. The NWS does take into account spotter reports all across the area for when they release snow total graphics as seen below.

snowfall recap nws

 

Although the official report will be looked at as 8.8″ it is known that across the Stateline anywhere from 8-18″ of snow fell during this event.

– Nick

 

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This post was written by Alex Kirchner on November 22, 2015

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