Oregon-AMS Meeting Summary
Tornado” by Dave Elson - Powerpoint, NWS, and Steve Pierce - Powerpoint
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
(Oregon), Puget Sound (Washington),
eastern Washington, and southern Idaho. Many remember the F3 tornado that hit Vancouver on April 5th,
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, ˝-inch hail was still spotted near I-5 and NE 134th Street. The boat dock east
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)