Metrics for the Sea Ice Outlook

This website describes metrics of spatial forecasts included in the Sea Ice Outlook. We ask that if you do submit processed fields to 2025 SIO, you include information on the forecast grid (latitude, longitude, grid area), and identify land points with the _FillValue attribute on the variable in the NetCDF file. If you received a username and ftp password prior to 2025, you should be able to upload to the data portal using these credentials. If you are a new contributor or have any other queries, please email Ed Blanchard-Wrigglesworth at edwardbw at uw.edu

  • Forecast initial conditions

    We invite dynamical model contributors to include spatial fields of their forecasts' initial conditions, particularly sea ice concentration and sea ice thickness or ice thickness distribution, with the date of initialization documented. If forecasts are produced from multiple initializations, these could be the mean fields across your intializations or you can include each single initialization.

  • Sea Ice Probability (SIP)

    SIP is defined as the fraction of ensemble members in an ensemble forecast with September ice concentration in excess of 15%.

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    Example of SIP forecasts (July 2018 SIP forecasts of September 2018).


  • Ice Free Date (IFD)

    Ice-free date (IFD) is the first date (quantified as day of year) in the melt season at which the ice concentration at a given location first drops below 15%. Below are the IFDs in observations since 2015 up to May 2019. If you can (new for 2020) we request that you also calculate IFD80, which would be an additional field of the first date at which ice concentration drops below 80%. This marks the start of the ice loss period.

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  • Ice Advance Date (IAD)

    Ice advance date (IAD) is the first date (quantified as day of year) in the freeze up season (ie after the summer minimum) at which ice concentration at a given date first increases over 15%. Below is an example of IAD for freeze up of 2016. The black contour indicates the sea-ice edge on September 15th (day of year 259). If you can (new for 2020), we request that you also calculate IAD80, an additional field of the first date at which ice concentration increases over 80%. This marks the end of the ice gain period.

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