MWOs are responsible for the preparation and dissemination of SIGMETS to appropriate ACC/FIC within their own and agreed adjacent FIRs. Aircraft in flight should be warned by the ACC/FIC of the occurrence or expected occurence of one or more of the following SIGMET phenomena for the route ahead for up to 500nm or 2hrs flying time:
(b) At transonic and supersonic cruising levels (see Note3) (SIGMET SST)
- moderate or severe turbulence;
- cumulo-nimbus cloud;
- hail;
- volcaninc ash cloud
Note 3: FL 250-FL 600 within London and Scottish UIRs, FL 400-FL600 within Shanwick OCA.
So as far as i can tell it's more to do with levels thans speeds
Last edited by TheFox; 1st Jan 2003 at 17:19.