What does this mean?

The maps and bar graphs show how Northern Hemisphere snow cover for different years and months compares to averages for the period 1966 to 2012. The maps show snow cover, expressed as the number of days a grid cell is snow covered for each month for each year. On the maps, areas with longer than average snow cover duration are indicated in blue (positive anomalies). Areas with shorter than average snow cover duration are indicated in red (negative anomalies). The maps of anomalies help show where changes in snow cover are strongest.

The bar graphs indicate the mean snow cover extent for the Northern Hemisphere for a given month. The graph helps to illustrate hemisphere-wide changes for each month. >>Continue reading...