The 'qvaci_iwxxm' collection consists of sets of polygons that show the expected ash areas for where ash exceeding the four concentration thresholds (0.2mg/m3, 2mg/m3, 5mg/m3 and 10mg/m3) is expected to occur. It includes one dataset, which provides only the vertical levels where the ash plume is present in the atmospheric layer between FL000 and FL600.
The IWXXM objects/polygons represent a subset of the gridded data with each spanning the minimum to maximum height for a given threshold. All the data sets are provided covering the period from T+0 hour to T+24 hours at 3-hourly intervals from the time they are issued. In the case of a significant volcanic eruption in Iceland, the IWXXM data will be updated every 6 hours while a significant ash cloud remains.
Payloads are in XML format, as per the IWXXM schema https://schemas.wmo.int/iwxxm/2025-2RC1/WAFSSigWxFC.xsd. Please note this is currently a release candidate, so it may be subject to further adjustment before it comes into effect in November 2025.
Please note that you cannot filter the IWXXM payloads to receive polygons for only one concentration threshold. The API response will return all the data for a particular forecast timestep.