By Rod Hill on 2010-12-15
PRELIMINARY LOCAL STORM REPORT...CORRECTED
NATIONAL WEATHER SERVICE PORTLAND OR
130 PM PST TUE DEC 14 2010
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1144 AM TORNADO AUMSVILLE 44.85N 122.87W
12/14/2010 MARION OR FIRE DEPT/RESCUE
EAST AND WEST BOUND LANES COVERED WITH DEBRIS NEAR TOWN
OF SHAW. MANY AUTO ACCIDENTS BETWEEN MILE POSTS 42 AND 45
DUE TO HAIL ON ROADS.
1144 AM TORNADO AUMSVILLE 44.85N 122.87W
12/14/2010 MARION OR BROADCAST MEDIA
DAMAGE TO MANY HOMES AND BUSINESSES IN AUMSVILLE.
OVERTURNED SEMI TRAILER. UPROOTED TREES. ALSO...MANY
REPORTS OF FLYING DEBRIS HITTING AUTOS AND OTHER
STRUCTURES...SUCH AS TWO BY FOUR LUMBER STUD BLOWN INTO A
TRUCK.
1144 AM TORNADO AUMSVILLE 44.85N 122.87W
12/14/2010 MARION OR FIRE DEPT/RESCUE
EMERGENCY PERSONNEL OBSERVED TORNADO. NUMEROUS TREES
DOWN. REPORTS OF PEOPLE TRAPPED IN AUTOS DUE TO NUMBEOUS
DOWNED POWER LINES.
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The above was issued by the National Weather Service. A number of stories and videos can be found at:
www.kgw.com
Damage in the videos showing roofs ripped off and walls of homes damaged indicate this was at least an
F-2 Tornado. Wind speeds were likely 113 - 157 mph in the vortex of the storm or higher.
Strong wind shear likely played a role in the tornadic development. An upper level disturbance tracked through
Clackamas county this morning, jet stream core winds were near 150 mph from the west/southwest. 5,000'
winds were near 50 mph mostly from the west. The shear would have been speed shear, meaning the difference
in speed from near 5,000' to 30,000' was great and can cause friction, leading to a spinning of air - coupled with
surface based rising air from a very unstable air mass and some rotation from the passing disturbance. The pattern
I just mentioned is not unusual for our area. As you know, tornadoes are rare. Oregon does in fact average several
tornadoes a year. Unfortunately, the random nature of development means the storms are almost always a complete
surprise with no warning. Our area does seem to be a greatest risk for mini - windstorms or in this case a tornado
when the flow pattern has a southwest component, an upper level disturbance and a strong jet core.
ALL THREE WERE PRESENT THIS MORNING.
Weekend Rain Totals