A snow cover extent (SCE) climate data record (CDR) has been derived from a thorough reanalyasis of NOAA visible satellite-derived maps of Northern Hemisphere (NH) continental SCE, maps that date back to late 1966. In 1999, the weekly NOAA maps transitioned to Interactive Multisensor Snow and Ice Mapping System (IMS) maps. Comparisons between climatologies of the first 33 years of coarse-scale weekly NOAA maps and the most recent 12 years of finer daily IMS maps, and a two-year overlap of independently-produced weekly products and trial IMS maps were used to generate a consistent, seamless SCE CDR. This included upscaling the finer spatial resolution IMS maps to the older weekly map resolution. The improved SCE CDR and associated products are available for viewing and downloading via the Rutgers Global Snow Lab website (http://snowcover.org) and through the National Snow and Ice Data Center.

SCE climatologies, time series and spatial analyses have been generated using the new CDR. One avenue of study has been to better understand SCE extent and variability. For example, spring SCE continues to decline over Eurasia and North America during the satellite era, while winter SCE has changed little and in recent years has frequently been quite extensive.. These winter-spring differences are often noted within a given year. The 2009/10 snow season was one where winter (December-February) snow cover was the second most extensive over North America (NA). This was followed by the least extensive NA spring (March-May) cover.

Principal component analysis (PCA) was performed on the annual cycle of NH SCE. Results for the first two compoents explain close to 60% of the vaiance, with the first component dominating the months of February through May and the second October through January. Based on the PCA score time series, snow area composites for years falling either +1 or -1 PC were created. Results for the NH snow composite analysis based on positive PC years displays greater SCE, in excess of 4 million square kilometers. Mid-troposheric geopotential height anomalies based on positive (negative) PC years are indicative of negative (positive) AO/NAO type phases.