In late 1997, NOAA/NESDIS began production of a daily Interactive
Multisensor Snowmap (IMS). This product is being implemented to
provide a daily Northern Hemisphere snowmap for use in specifying the surface boundary conditions in numerical weather forecast models run by the National Center for Environmental Prediction (NCEP). The daily IMS snowmaps will replace a weekly snowmap that NESDIS has been producing since 1966. There is concern in the climate community that the new multisensor product will cause a discontinuity in the long-term record. It is critical that for an overlap period, NESDIS produce both the weekly and the daily snowmaps and that a detailed validation of both products be done. It is also very important that a comparison between the two snowmaps be undertaken to determine what differences occur between the products and why and under what circumstances the discrepancies occur.
The weekly NOAA snow product is produced from visual analyses of
visible satellite imagery by trained meteorologists. It is the longest satellite-derived environmental data set available and plays an important role in the monitoring of climate variability and change. The IMS product employs visible imagery, passive microwave data, and station data in the daily charting effort, which is done interactively by trained meteorologists on a work station.
NESDIS management has agreed to generate both the weekly and daily snowmaps for 15 months covering a complete northern hemisphere snow season, and funding for a validation effort is being provided to the authors through the NOAA/NASA Enhanced Data Set Program. Here we report on both the weekly and daily products, independent data sets being collected for product intercomparisons, and results of the validation effort to date. This project will make the transition between the two products as seamless as possible and will also provide input for the improvement and refinement of the new daily product.