Snow forecasts in Washington state are pretty horrible. I actually am not sure they have ever accurately predicted snowfalls. Anyways, my favorite weather blogger, Cliff Mass posted a couple of articles on why forecasting is really hard sometimes. A bit weather-nerdy, but insightful.
Weak disturbances that develop on fronts, or frontal waves, are relatively small scale, are often shallow, and are very difficult to forecast correctly even over land. But in this case, it is even harder because they are forming and evolving over the ocean where our ability to detect and describe small-scale structures are not as good. And the snow events this week have all been associated with such frontal waves and to forecast the snow correctly requires getting their position, size, and motion exactly correct…something current weather prediction technology is still not adequate to deal with.
There are at least three reasons:
- The description of the atmosphere, the starting point of the simulation called the initialization, is flawed.
- The physics of the model, how basic processes like radiation, clouds and precipitation are described, are flawed.
- The forecasting problem is not possible considering the inherent uncertainties of atmospheric flows and the tendency for errors to grow in time.