Help - problems with understanding the plot?


You are looking at a quite simple plot of time series. The values on the vertical axis inform about the fraction of a country (Poland in this case) is currently covered with snow. Instead of absolute units (square kilometres) a relative value is given, which is the percentage of a country territory. The scale is simple: 0% means now snow at all, while 100% the whole country under snow cover. The horizontal axis represents time, i.e. the consecutive days of a year, starting July 1 and ending June 30. The New Year falls exactly in the middle of the plot and is marked with a continuous vertical line. Vertical dashed lines indicate the first day of each month.

The plot shows two lines. The red line represents the extent of the snow cover in the current season. Information is daily updated. The most recent value (right-most) informs about the snow cover 1-2 days ago. Delay is caused by the time needed for data analysis. The blue line in the background of the plot indicates the average snow cover for given day, based on climatological data (winters since 2004, excluding the current season).

The average may serve as a reference point for the interpretation of the line for the current season - indicates whether the presence of snow cover, and its coverage at any given time are unusual, or typical. For example, the blue line shows that snow cover appears in Poland first in the middle of October, and is noted until the end of April. However, the greatest probability of snow cover occurrence in Poland is in January and February. Nevertheless, one should not expect snow in the period from May to September (except for the mountains).

The graphs show only the snow cover presence, without specifying its depth. On the map and plots the snow cover is marked it the same way, despite being 1 cm depth or 100 depth. This is due to the nature of the optical remote sensing of snow.


© 2010-2015  | Earth Observation Group at CBK PAN
Data analysis and web site concept: Andrzej Kotarba
Web site maintenance: Andrzej Kotarba and Adam Włodarkiewicz
Contact info:

Centrum Badań Kosmicznych PAN

Web site was partialy deweloped under the framework of the following projects:
  GEO Network for Capacity Building - GEONetCab (, 2009-2012
  Earth Observation for Economic Empowerment - EOPOWER (,

Disclaimer: We put our best effort to make this web site as accurate as possible. Nevertheless the web site comes with no warranty to its users. By using this web site and/or data published on this web site you acknowledge, that you are doing this on YOUR OWN risk and responsibility. Acknowledgement: Source data used by this web site (The Interactive Multisensor Snow and Ice Mapping System, or IMS) originates from NOAA servers and are freely available for everyone at