Oregon-AMS Meeting Summary

“2008 Vancouver Tornado” by Dave Elson, NWS, and Steve Pierce

We had 34 attend this technical meeting. Columbia River Inter-Tribal Fish Commission hosted the meeting. Our guest speakers were Dave Elson, Lead Forecaster, from the Portland NWS Office, and Steve Pierce (Storm Chaser). This was also a “dessert meeting,” so yummy desserts were shared. Kyle Dittmer presided over his last meeting as outgoing Oregon-AMS President.

Dave started the talk by showing the tornado climatology of the Pacific Northwest. Generally, F0-F1 tornadoes strike the region, with a few F2/F3 reports. Sittings tend to cluster in the Willamette Valley (Oregon), Puget Sound (Washington), eastern Washington, and southern Idaho. Many remember the F3 tornado that hit Vancouver on April 5^th, 1972. Common factors for local tornado formation include: post-cold front, cooling aloft, and moderated surface marine air. Geographic channeling helps make wind shear. In the case of the January 2008 storm, horizontal convective rolls were a key source of rotation.

On January 10, 2008, the Portland CAPE values were much higher than the models suggested, with the NAM forecasting 238 J/kg, compared to the actual (estimated) 912 J/kg. The storm was a super-cell with an overhanging top. NEXRAD (Doppler radar) showed a “hook echo” in red, which is a strong sign of a tornado vortex. A notch in the gust front, prior to tornado development, indicated enhanced wind shear and rotation. The tornadic vortex wind shear was 68 knots at its peak.

Damage was mostly confined to the east side of Vancouver Lake. The tornado was classified at EF-1 (enhanced Fujita scale) or 90-110 mph. The track was 10 miles. The damage included 200 down trees, 30-40 homes impacted, totally $525,000, but no deaths or injuries. These tornadoes are rare but are favored by north-south oriented valleys and local terrain (slope influence by the Portland West Hills?). Two of the three most significant tornadoes to hit southwest Washington and northwest Oregon in the past 50 years touched down within a few miles in Vancouver.

Steve then gave a detailed photo slide show of the damage sites: ripped roofs, downed signs, snapped trees, sheared trees and branches, uprooted trees, and downed power lines and poles. An hour after the tornado passed, ½-inch hail was still spotted near I-5 and NE 134^th Street. The boat dock east of Vancouver Lake had metal roof strips wrapped around trees, suspended 100 feet in the air. Trailers at the boat launch were destroyed. A fish was lifted from the lake and thrown a mile to NW Dale Road.

Note-taker: Kyle Dittmer, Oregon-AMS President (2005-2009)