  Accurate forecasting of the arrival time and subsequent geomagnetic impacts
of Coronal Mass Ejections (CMEs) at Earth is an important objective for space
weather forecasting agencies. Recently, the CME Arrival and Impact working team
has made significant progress towards defining community-agreed metrics and
validation methods to assess the current state of CME modeling capabilities.
This will allow the community to quantify our current capabilities and track
progress in models over time. Firstly, it is crucial that the community focuses
on the collection of the necessary metadata for transparency and
reproducibility of results. Concerning CME arrival and impact we have
identified 6 different metadata types: 3D CME measurement, model description,
model input, CME (non-)arrival observation, model output data and metrics and
validation methods. Secondly, the working team has also identified a validation
time period, where all events within the following two periods will be
considered: 1 January 2011-31 December 2012 and January 2015-31 December 2015.
Those two periods amount to a total of about 100 hit events at Earth and a
large amount of misses. Considering a time period will remove any bias in
selecting events and the event set will represent a sample set that will not be
biased by user selection. Lastly, we have defined the basic metrics and skill
scores that the CME Arrival and Impact working team will focus on.
