No, I am NOT kidding. When she blew in '80 we proceeded to have the WORST drought EVER. Even in the midwest. Her destruction was NOT just WA. She has been spouting off for 15 months now.
Mt. St. Helens isn't erupting, it's fairly quietly building a dome; gas emissions, relatively for a volcano, are minimal, and it has absolutely nothing to do with your drought.
Nor did the Mount St. Helens eruption in 1980, which wasn't big enough for any weather effects anywhere either.
You either need a truly big eruption (like Pinatubo in 1991) or an eruption emitting unusual amounts of Sulfur Dioxide, like El Chichon in Mexico in 1982, to affect climate.
Droughts in the Great Plains of the US are common because they're quite close to being desert. The "Dust Bowl" in the 1930s had nothing to do with volcanism.
Correlation is not causation, particularly with one data point. And there isn't even a second data point because MSH hasn't even really erupted recently.
Good article on what caused the "Dust Bowl" drought in the 1930s...
http://www.nasa.gov/centers/goddard/news/topstory/2004/0319dustbowl.html
Basically you get a horrific drought in the Great Plains when the Tropical Pacific is cool and the Tropical Atlantic is warm, as in the 1930s, shifting the jet stream.
Unfortunately, you can see the exact same conditions prevail now:
https://www.fnmoc.navy.mil/products/NCODA/US058VMET-GIFwxg.NCODA.glbl_sstanomaly.gif
It's a long-term ocean SST cycle with no relation to volcanism.
And this could go on for YEARS.
