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.

Hail in LANE, OREGON
From 04-JUN-09 13:02:00 to 04-JUN-09 13:02:00 (PST-8)
Location: MABEL
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Large hail was accompanied by heavy rain as the storm passed.

Hail in LINN, OREGON
From 04-JUN-09 13:02:00 to 04-JUN-09 13:02:00 (PST-8)
Location: ROWLAND
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Large hail was accompanied by heavy rain as the storm passed.

Thunderstorm Wind in BENTON, OREGON
From 04-JUN-09 14:30:00 to 04-JUN-09 14:30:00 (PST-8)
Location: CORVALLIS
Magnitude: 71.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Thunderstorm Wind in MARION, OREGON
From 04-JUN-09 14:55:00 to 04-JUN-09 14:55:00 (PST-8)
Location: SALEM
Magnitude: 70.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Public

A report called in by a former spotter, strong gusty winds brought numerous trees down along Hwy. 22.  Other reports from this storm included wind gusts strong enough to snap Cottonwood tree branches estimated at 10 to 12 inches in diameter along Hwy. 214.

Thunderstorm Wind in MULTNOMAH, OREGON
From 04-JUN-09 16:15:00 to 04-JUN-09 16:15:00 (PST-8)
Location: PORTLAND
Magnitude: 56.00 EG
Property damage: 1.20K
Crop damage: 0.00K
Reported by: Newspaper

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.

Thunderstorm Wind in WASHINGTON, OREGON
From 04-JUN-09 15:50:00 to 04-JUN-09 15:50:00 (PST-8)
Location: SHERWOOD
Magnitude: 52.00 EG
Property damage: 0.80K
Crop damage: 0.00K
Reported by: Newspaper

Outside of Chapters Books and Coffee in Newberg, a tree with estimated diameter 10 to 12 inches was snapped in half. Also, numerous spotter reports just to the north and  with similar conditions were reported.

Thunderstorm Wind in CLACKAMAS, OREGON
From 04-JUN-09 15:50:00 to 04-JUN-09 15:50:00 (PST-8)
Location: ESTACADA
Magnitude: 52.00 EG
Property damage: 1.20K
Crop damage: 0.00K
Reported by: NWS Storm Survey

NWS Storm Survey visited a site with extensive damage most likely the result straight-line thunderstorm winds.  Numerous large tree branches ranging in diameter of 10 to 16 inches snapped off of several trees.  The wind speed is estimated from damage in a nearby county under similar conditions.

Tornado in LINN, OREGON
From 04-JUN-09 14:35:00 to 04-JUN-09 14:45:00 (PST-8)
Location: PEORIA
Tornado F-scale: EF0
Property damage: 10.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

A tornado was reported by the public to local television station KVAL in Eugene. NWS Storm Survey visited the residence and confirmed: a small shed-like structure was lifted off the ground and blown 21 feet to the east - counter to the prevailing storm winds.  There were also circular carvings in the grass nearby.

Thunderstorm Wind in MULTNOMAH, OREGON
From 04-JUN-09 16:30:00 to 04-JUN-09 16:30:00 (PST-8)
Location: PARKROSE
Magnitude: 52.00 EG
Property damage: 0.30K
Crop damage: 0.00K
Reported by: NWS Employee

At the Portland WFO, strong wind gusts knocked down a small tree in the parking lot, as well as snapped off a large branch from a different tree on the property.