To do this, we will be examining the accuracy of forecasts produced by the Hydrometeorological Prediction Center (HPC), which provides precipitation forecasts and outlooks for the entire continental United States.
The metric that they use to evaluate the accuracy of their forecasts is known as the equitable threat score. Without getting into the gory details, the bottom line is the higher the equitable threat score, the more accurate the forecast.
Forecasts produced by computer models (i.e., the NAM and GFS) and by the HPC forecasters show considerable progress going back to the beginning of this record in 1993 (and certainly much progress before that). For example, for storms producing an inch of precipitation (snow-water equivalent) in 24 hours, the NAM and GFS equatable threat scores have climbed from about .15 in 1993 to about .25 in 2006, with some evidence of a plateau thereafter.
So, forecasts are better today than they were 10 or 20 years ago, and there have been some major forecast victories (e.g., Hurricane Sandy) that could not have been achieved with the tools and models of 20 years ago.
However, those statistics are for the entire United States. While it is likely that forecasts have improved everywhere since the early 1990s, they haven't improved uniformly. If we look at the equitable threat scores for precipitation forecasts from 16 April 2011–15 April 2012 by region, we find they are highest along the U.S. west coast and in the northeastern U.S., and lowest in the western U.S. interior and southeast U.S. This holds for both modest (a threshold of 0.5") through large (2.0") 24-hour accumulation thresholds, although there is more scatter in the highest bin due to the small number of events.
|Equitable threat scores for HPC and calibrated ensemble modeling system|
forecasts from 16 April 2011–15 April 2012 by region. Courtesy
Keith Brill, HPC
Based on these statistics, the most reliable snow forecasts are likely to be for the Cascades and Sierra, followed by the Northeast, and then the interior (e.g., Utah, Wyoming, Montana, Colorado). Wasatch powderhounds who feel battered and bruised by forecasts have every right to complain to their brethren to the west. However, while we don't know precisely when or where a storm will produce, we don't have to worry as much about snow quality.
Of course, there are some caveats to this analysis. It would be good to examine statistics strictly for winter. Snow forecasts in the Sierra and Cascades also depend on the snow level forecast, and this can be a challenge in some storms. Finally, there is the issue of converting from snow-water equivalent to snowfall amount, which contributes to errors in the forecast of snow amount. Nevertheless, if these factors are considered, I think we will find that the interior west remains the most difficult ski region in which to forecast snow.