We understand that you are asking the same questions like us — how deep was the snow yesterday or two days ago? How did it change with the recent storm? What is the snow depth today? Whether you’re new to our snow modeling product mountainsnow.org or already an accustomed user – it has just gotten better and much more useful to you!
The snowpack responds to the weather, it’s as simple as that. So, at Community Snow Observations, we force our snowpack models with weather data. Since there are not weather stations everywhere we would like, we force our snow models with ‘gridded’ (think checkerboard) output from weather models. Some weather models are reanalysis models and they use current weather station data to create their gridded results of current and past weather. Other models are forecast models that predict weather into the future, with uncertainty that increases the farther out you go.
Because of the time requirements for running computer models and thus lag time in data availability, it is currently not possible to get reanalysis data that is closer to today’s date than three days ago. In the past, CSO has used reanalysis data, which means that snowpack results shown at mountainsnow.org stopped at ‘three days before yesterday’(n-4, see graphic below). So, if you went to mountainsnow.org on March 28, you could not see the snowpack results for March 28, 27, or 26, but you could see the results for March 25 (n-4). In addition to delay in reanalysis data availability, once the data comes available, it takes our computers approximately one full day to digest all the input data, apply corrections and compute the final output (what you see on mountainsnow.org). We have changed our modeling approach and we now use forecast data to ‘close the gap’ and provide snowpack results up to and including today! Visit mountainsnow.org to see up to date information on what the snow is doing in our high mountain areas right now.
As the graphic above shows, our computers running today (n) uses a combination of reanalysis data and forecast data to provide the snowpack results for the last couple of days (n-1 and n-2), and because of the computing requirements, it is tomorrow’s (n+1) forecast data that’ll be the basis for what is shown as tomorrow’s ‘today’s snowpack’. [Confusing enough, huh?!] If you look at today’s snowpack in a week from now, the snowpack that was shown on today’s date will no longer be based on the forecast data but instead replaced with reanalysis data (better accuracy) and also corrected by snow depth information submitted by CSO participants.
What’s next? Well, as already stated, uncertainty increases the farther you go into the future, and that holds true especially in complex mountainous terrain which is notoriously difficult to forecast. That being said, we are working on a snowpack forecasting product that extends a couple of days into the future — so keep your ears out for the next up-date on mountainsnow.org!