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During most winters, storms bring long periods of heavy rain and snow to the
Pacific Northwest. In addition to extended rain, flooding can also occur due to
ice jams, where large flows of ice pile up. This pile-up of ice can act like a
dam, causing water to back up and flood. Warm weather can also cause snow on the
middle and higher mountains to melt, putting more water into already rain-swollen
streams.
Flooding causes more deaths and prpoerty damage in the U.S. than any other severe
weather related event. The majority of flood related deaths occur when people
become trapped in automobiles while attempting to drive through flooded areas.
Flowing water can be deceptively strong, and pack a powerful punch. As little as
six inches of water is enough to float a small car and carry it away. There
have been many floods in the history of the Northwest, which include the
devastating floods of December 1964 and February 1996. Most recently, in Dec 2007 and Jan 2009,
significant flooding struck the Pacific Northwest, closing a twenty mile stretch of
interstate 5 near Chehalis Washington under 10 feet of water. Coastal flooding
can also occur during the winter months, and poses a threat to life and property.
Winds generated from very strong Pacific storms can drive ocean water inland, much
like a storm surge, and can cause significant flooding along the immediate coastal
areas and estuaries.
A Flood refers to a gradual rise in the water along a stream, river, wash or over
an extended period of time. Floods result from heavy rainfall, river ice jams,
snowmelt. They can erode an entire
mountain side, roll boulders the size of trucks, tear out trees, destroy buildings, wash out roads and
bridges, and cause the loss of lives. Rain weakened soils can also result in mudslides capable of closing
major highways.
Flood Watch...
This means that flooding is possible with the watch area. You should remain alert and be
ready to evacuate on a moment's notice.
Flood Warning...
This means that flooding has been reported, or is imminent. When a flood warning is issued
for your area, act quickly to save yourself. If advised to evacuate, do so immediately.
Go to higher ground, or climb to safetly. Move to a safe area before access is cut off by rising flood waters.
Nearly half of all flood fatalities are auto-related. Water that is two feet deep will
carry away most automobiles. Never attempt to drive through a flooded roadway. The road bed
may be washed out beneath the water, and you could be stranded or trapped. If the vehicle stalls,
leave it immediately and seek higher ground.
The best advice if you are in a vehicle: TURN AROUND…Don't DROWN.
From the past...
Record Floods of December 1964 [some historical photos]
The December 1964 rainstorm was undoubtedly the most severe rainstorm to ever
occur over central Oregon, and among the most severe over western Oregon since
the late 1870s. Several observing stations across central Oregon recorded
two-thirds of their normal annual rainfall in just 5 days. Scores of stations
set new records for both 24-hour totals and December monthly rainfall totals.
Widespread severe flooding occurred, with at least 30 major highway bridges
receiving such damage as to make them unuseable! The new John Day multi-million
dollar bridge was destroyed as were scores of bridges on county and secondary
roads. Hundreds of miles of roads and highways were washed out or badly damaged.
Thousands of people had to be evacuated due to ensuing floods.
The Willamette
River at downtown Portland had a stage of 29.8 feet. This was a record high for
the winter season, and was within inches of the peak stage during the Columbia
River spring flood of 1948. Hundreds of homes and other buildings were destroyed
and an even greater number were badly damaged. .Heavy snow followed by
persistent heavy rains lead to record flooding in Oregon during the later half
of December 1964 and January 1965. In all, 17 people died. Virtually every river
in the state was far above flood stage and mudslides, bridge failures, and
inundation closed the state's roads, airports, and railways. Reservoirs were
overwhelmed early on in the storm and many proved unable to release water fast
enough to prevent overtopping. Dorena Dam, south of Eugene had water flowing
over the top more than 8 feet deep.
Read more information on this and other historic storms in Oregon.
Additional Links of Interest...
- 1996 Flood Summary of Northwest Oregon/SW Washington
- Historic Floods of Oregon
- Severe Emergency Plan for Inland Pacific NW Schools
- Each local office may have photographs online (see office links below)
Remember, in times of severe weather, you can get all these vital NOAA/National Weather Service messages via NOAA Weather Radio, your favorite
local media, or through NOAA's National Weather Service websites.
For questions about local Severe Weather Preparedness, contact your local NOAA National Weather Service Office:
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