At approximately 2200 UTC 10 July 1998, an aircraft over southwestern British Columbia reportedly was forced to divert around a volcanic ash cloud. A pilot on the aircraft, flying at approximately 31 thousand feet was quoted as saying "I have not seen anything like this since Mount St. Helens erupted". Immediately thereafter, an investigation commenced to determine the source of this cloud; concurrently, SIGMET messages were issued and emergency response procedures activated.
The event is chronicled, with an emphasis on the SIGMET messages and the various real-time reports. Backward and forward trajectories are used to demonstrate the probable source of the suspected ash cloud as well as its forecast motion, respectively. It will be shown that this ash travelled for several days over the Pacific Ocean before being reported over British Columbia. Satellite imagery and trajectories are examined to determine if this ash could have been detected prior to its arrival over the busy airways of western North America. Finally, the operational response and impact on the aviation industry will be assessed with specific reference to the challenge of effective warning of an ash event from an unknown or unconfirmed source.
The 8th Conference on Aviation, Range, and Aerospace Meteorology