…Flooding and flash flooding…a significant threat to life and property across the Pacific Northwest…

"Flash floods are a significant concern in the region because of our rugged terrain,” said Mike Vescio, Pendleton , Ore. , weather forecast office Meteorologist in Charge. “On June 14, 1903 , the worst natural disaster in Oregon history occurred when a flash flood swept through Heppner destroying the town and claiming about 250 lives during the second worst flash flood fatality event in American history."

What is the difference between a flash flood and river flooding? Flash flooding occurs within a few hours of the heavy rain event and ends a few hours after it starts. River flooding takes half a day or longer to develop and frequently rivers will remain above flood stage for days at a time.

Flooding and flash flooding occur every year at some location across the Pacific Northwest. Since 1986, over 700 floods and flash floods have been reported somewhere in the states of Idaho, Oregon, or Washington. This is an average of over 27 flash flood events per year. Some years there are only a few events, but in a bad year more than 75 such events can occur.

As long as a significant snowpack remains in the mountains…spring storms could cause rapid rises in area rivers and streams. Rain falling on the heavy snow pack has the potential to cause rapid snowmelt, flooding small streams and even larger rivers. This year's heavy snow pack will remain in the higher elevations until early july. This will keep an elevated risk of river flooding across the Pacific Northwest into early summer.

An additional flooding threat across the Pacific Northwest is flash flooding due to heavy downpours from thunderstorms. FLASH FLOODING from thunderstorms is caused by the rain falling faster than it can be carried away by normal drainage channels. The result is rapid rises in small streams as the large volume of water races downstream.

A flash flood refers to a dangerous sudden rise in water along a stream, river, wash, or over a normally dry land area. Flash floods result from heavy rainfall, river ice jams, snowmelt, and dam or levee failures. Flash floods can occur within a few minutes or hours, and can move at surprisingly high speeds, striking with little warning. 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 loss of lives. Rain weakened soils can also result in mud slides capable of closing interstates.

To stay informed about a flash flood listen for:

A Flash Flood Watch…

This tells you that flash flooding is possible within the watch area.  You should remain alert and be ready to evacuate on a moment's notice.

A Flash Flood Warning...

This tells you that flash flooding has been reported or is imminent. When a flash 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 safety. Move to a safe area before access is cut off by flood water.

An Urban and Small Stream Flood Advisory…

This tells you that flooding of small streams...streets and low lying areas such as railroad underpasses and urban storm drains, is occurring, but rainfall is not expected to produce a flash flood situation.

The following basic flash flood safety rules should be observed when you see flooding or hear about a flash flood warning…

Do not camp or park your vehicle along streams and washes, particularly during threatening conditions.

If you are near a river be aware of water levels and be prepared to take action to move to higher ground if river levels rise.

Do not enter areas that are already flooded.

Do not try to cross a flowing stream on foot when the water is at or above your knees.

If walking or fishing along a river, be aware that erosion from swift running water can cause river banks to collapse.

Never let your children play around high water, storm drains, viaducts or arroyos.

Be especially cautious at night when it is harder to recognize flood dangers.

Nearly half of all flash flood fatalities are auto related.  While driving your automobile look out for flooding at highway dips, bridges and low areas.  Two feet of water will carry away most automobiles.  Never attempt to drive over a flooded road.  The road bed may be washed out under the water and you could be stranded or trapped.  If the vehicle stalls, leave it immediately and seek higher ground.  Rising water may engulf the vehicle and sweep it away.

THE BEST ADVICE IF YOU ARE IN A VEHICLE…TURN AROUND…DON'T DROWN.

During flash flood season, and year round, stay abreast of the latest weather information.  You can receive the latest forecasts and immediate notification of warnings on NOAA weather radio.

From the past...
Deadly Flash Flood on June 14, 1903 at Heppner, Oregon [ historical photo ]
This was surely the most deadly natural disaster in Oregon's recorded history. A strong thunderstorm, accompanied by extremely heavy rain and hail, moved near Heppner, Oregon. The storm covered a very small area, probably no more than 50 square miles. Heavy rain fell in a very short time, creating severe flash flooding along Willow Creek, normally a peaceful stream flowing through the town center. The entire town was swept away in just a few short minutes, drowning 247 people. Eyewitnesses say thunderstorm rains arrived as a 40-foot wall of water and the ensuing flood raged through town for over an hour. In all, one-third of the towns' structures were wiped out. The massive runoff of water was a result of heavy rain falling on the barren rocky hills, then flowing into the Willow Creek watershed. Only fifteen minutes separated the first rainwater in Willow Creek at Heppner and the flood crest! There are no rainfall records available for this storm because the weather observing station was completely destroyed, drowning the observer and his entire family.

A similar fate would have been in store for the citizens of Ione, just 20 miles downstream. However, telephoned warnings prompted an immediate evacuation and residents escaped to high ground. At least 150 homes were destroyed at Ione and bodies were washed more than 40 miles downstream to the Columbia River.

Additional Links of Interest...
1. Historic Floods of Oregon
2. Severe Emergency Plan for Inland Pacific NW Schools
3. Each local office may have photographs online ( see office links below )