http://www.opc.ncep.noaa.gov/Loops/

You want the "Pacific Products" page and select the charts for the "North Pacific Surface Analysis". If you are running Linux you need to select the Javascript application.

Look at the blocked situation on the west coast of North America. When a Low pushes through two fairly far apart anticyclones, tornadoes tend to dominate.

When the anticyclones are virtually connected as is the case with the egg-timer shaped system off the coast on the 21st, the situation is relieved as volcanic events predominate.

http://weathercharts.wordpress.com/2...and-volcanoes/