The South Valley Surprise of 2002 was a Pacific Northwest windstorm that affected the U.S. states of Oregon, Washington, California, Nevada, and Idaho on February 7, 2002.
The circulation was so small in area that the isobars were compacted tightly, thanks to a strong ridge of high pressure to the south, resulting[clarification needed] in sustained winds of 50 mph with gusts above 70 mph.
[1] The "surprise" was how rapidly the storm organized and matured, and its unanticipated strength.
The storm was able to tap into the jet stream and aim it towards the surface the phenomenon known as "Jet stream enhancement", which usually occurs in the unstable air found in a cold front in a mid latitude cyclone.
The result was extensive damage to structures both directly and indirectly from falling trees and debris.