National Weather Service United States Department of Commerce


Across the Inland Northwest, river floods occur most often in association with rain and snowmelt from late winter into late spring. The flash flooding can happen anytime of the year, but July and August are the prime months for thunderstorm induced flash flooding.

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, 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.

Water covered roadways near Moscow, ID 3/14/03.




  • Flooding is possible
  • Be ready to evacuate
  • Flooding is imminent or occuring
  • Evacuate to high ground
  • Minor flooding expected
  • Not considered life threatening


You may not always have a warning that these deadly sudden floods are coming so you need to know some basic flash flood safety rules.

  1. Do not camp or park your vehicle along streams and washes, particularly during threatening conditions.
  2. 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.
  3. 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.
  4. If walking or fishing along a river, be aware that erosion from swift running water can cause river banks to collapse.
  5. Never let your children play around high water or storm drains.
  6. 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 its occupants and sweep them away.

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

For more information on Flash Flooding, visit the "Turn Around Don't Drown" National Weather Service web page