92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Sunday, 22 January 2012
Assessing the Feasibility of Forecasting Regional Snowfall Indices
Hall E (New Orleans Convention Center )
William S. Lamberson, NOAA/NESDIS/NCDC, Asheville, NC; and M. F. Squires

NOAA's National Climatic Data Center (NCDC) recently finished developing a regional snowfall impact index. This scale, know as the Regional Snowfall Index (RSI) is based upon a snowstorm's spatial extent, the amount of snowfall it produces, and the juxtaposition of these elements with the population it impacts. In the past, RSI has only been used to assess storms that have already occurred and it has never been used in a predictive manner. This is due to the general consensus that Numerical Weather Prediction (NWP) models have been and still are not accurate enough in their prediction of precipitation type, snowfall amount, and the areal distribution of snowfall to use snowfall impact scales like RSI in a predictive manner. The goal of this research is to evaluate this notion and determine if issuing a forecasted RSI score before a storm hits is feasible.

To accomplish this, a hindcast study was conducted. Archived NWP model output was manipulated to create a storm total snowfall forecast map for a select set of past snowstorms. From these maps, forecasted RSI values were computed and appropriately categorized. Then, to evaluate the feasibility of issuing a forecasted RSI, various categorical forecast verification metrics were used to compare the forecasted RSI values and categories to their corresponding observed values and categories. Results showed that the snowfall forecasts created from NWP data consistently overpredict RSI values. The study is currently being conducted again utilizing NWP output and a simple 10-to-1 snow-to-liquid ratio. Preliminary results show that this method produces a more accurate RSI forecast.

The benefits of being able to issue a forecasted RSI value for an impending snowstorm are simple yet highly important. Issuing a forecasted RSI score for an impending snowstorm would help convey the societal impacts of the impending storm to transportation officials, emergency managers, the media, and the general public. This would allow these entities and those who rely on their information to better prepare for an impending storm. Better preparation on the part of management officials and the general public would likely reduce the amount of human and financial losses caused by snowstorms.

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