Thunderstorm Wind in Multnomah County, Oregon

The top of a 70-foot tree, estimated between 20 and 20 inches in diameter, was snapped off in downtown Portland at the intersection of SW Salmon Street and Park Avenue. A passer-by was nearly hit as it fell to the ground. Time of the event is estimated based nearby reports from the storm.

A fairly vigorous upper level low pressure system had been blocked offshore and was finally allowed to progress onshore on June 4th. An upper level disturbance rotated around upper level low pressure system, enhancing divergence aloft and turning upper level flow easterly across much of western Oregon. This overall pattern resulted in enhanced vertical wind shear for the Willamette Valley, with southerly winds near the surface backing to easterly flow aloft. The June 4, 2009 was a significant thunderstorm outbreak by Northwestern Oregon standards, with several areas taking damage from strong thunderstorm wind gusts, minor urban area flooding, and rotation in a few storms resulted in one weak tornado.