The IWXXM SIGMET Subscription and Request Service Request Interface shall support filtering based on the ICAO location indicator of the FIR/UIR/CTA of interest. The IWXXM SIGMET Subscription and Request Service Subscription Interface shall allow for the selection of subscription based on clearly defined criteria. The service may support other filters based on the operators defined in the OGC Filter Encoding 2.0 Encoding Standard on a case by case basis.