Editor’s Note: This is a weekly column written by Meteorologist Joel Gratz that will take you “behind the scenes” of the typical weather forecast. Joel is the founder of ColoradoPowderForecast.com, where you can sign up for his email alerts.
Boulder, CO – Just like no two snow flakes are exactly the same, no two snowstorms are exactly the same. Most resorts report the number of inches of new snow accumulation, which of course is the major data point for most people. However, savvy skiers know that new snow depth is just one guide of how much fun you’ll have on the hill. Another very important aspect is the density of new snow, which is different for each snow storm. Low density, fluffy snow can often make the best memories, but it’s also somewhat rare.nThe density of snow is mainly controlled by the amount of moisture in the air and the temperature. Readings around 5-15ºF with lots of moisture often produce the fluffiest snow, but this is also dependent on the wind. High wind speeds make snowflakes crash into one another, which makes them break into smaller pieces. Smaller flakes pack more closely together when they accumulate, and this gives the feeling of slightly heavier, denser snow.
Weather computer models actually do a pretty good job of predicting the overall amount of moisture that will fall during a storm, but they don’t do a good job of predicting the density of the snow.
Thankfully, some very smart folks at the University of Utah created a specific computer model to predict the density of snow for the Alta area. Clicking on that link, the middle graph shows the density, where 15:1 is about average, 10:1 would be considered on the heavy side (for Utah), and 20:1 is blower powder.
We’ll see how this new technology proves out over the remaining storms this winter. Hopefully it helps forecasters to predict the quality of an upcoming powder day in addition to its depth.