May 18th marks the 40th anniversary of the eruption of Mt St Helens. As a young meteorologist with the National Weather Service in Seattle, I was on duty that fateful Sunday morning working the aviation forecast desk. At that time, we were a state forecast office. So I was responsible for 14 air terminal forecasts and close to a dozen air route forecasts statewide.

A few minutes after 830 AM, the red phone on the forecast desk, the phone that never rings, rang. The FAA Flight Service Station at Boeing Field was on the other end and patched me through to a pilot who was conducting a sightseeing tour around the volcano with five passengers onboard. In an excited voice over his radio, he said the mountain just blew, they were fortunately on the south side of the volcano, and they were now flying south toward Portland. He just wanted to know how to avoid the volcano ash plume and get back to his base at Chehalis.

Since the holidays in 1979 when the mountain started grumbling with swarms of earthquakes, we had pre-set plans with the partners like the U.S. Geological Survey, U.S. Forest Service, the FAA, the state of Washington and the counties around the volcano. Among those plans was a twice daily plume trajectory forecast up to 50000 feet.

That morning, the plume trajectory had it moving east toward Spokane. I informed the pilot he could follow the Cowlitz river north of Kelso and safely return to Chehalis. He also told me his plane had been hit by rocks and debris when the mountain blew, it felt like opening a very hot pizza oven, twisted the plane vertical with the wings pointed to the sky and ground, and there was lightning in the plume. The passengers? Well, let’s just say I heard R-rated language in the background.

Once off the phone, I turned to my lead forecaster on duty and said the mountain blew. We executed our plans, activating EBS – the Emergency Broadcast System – for a flash flood warning for the Toutle River via NOAA Weather Radio. I then called the FAA’s Air Route Traffic Control Center in Auburn to let them know of the eruption and the plume trajectory. They in turn shut down the air space from the volcano eastward and rerouted aircraft already in that air space. My next step was to update all the Eastern Washington terminal and air route forecasts, putting volcano ash into them and essentially shutting down the airports there. There were other actions, but all them were done in less than a hour.

After that, it was monitoring the situation, providing updates as needed, and addressing media phone interviews. We all have career moments – ones we remember above all. The eruption of Mt St Helens was my first career moment.

Mt St Helens is by far the most active of the Cascade volcanoes in Washington. Glacier Peak is estimated to have last erupted about two centuries ago. Mt Baker last did so in 1880 and Mt Rainier in 1894. Emergency managers have plans to address the next eruption of any of these volcanoes and exercise those plans periodically.

Now it is your turn. Share your May 18th Mt St Helens eruption story with us in our comments section.