Fall Severe Weather Preparedness Week Day 4: Flash Flooding

What are the types of flooding?

Many types of flooding occurs in Mississippi. Flash flooding, which can occur any time of year, is a result of sudden, heavy rainfall commonly produced from slow-moving intense thunderstorms or multiple rounds of thunderstorms occurring over the same area. Flash flooding can also occur with a dam or levee failure. Flash floods become raging torrents of water which rip through creek beds, city streets, and areas of poor drainage, sweeping away everything before them.

Another common type of flooding that occurs in Mississippi is river flooding. Many big river flooding events have occurred in the spring months from spring thunderstorms and snow melt upstream. However, history has shown that major river flooding can also occur in the fall and winter months, primarily from heavy rain.

Past Flooding Events

One significant winter river flood event came in February 1961, when a series of three storm systems tracked through the South, dumping extreme amounts of rainfall. Accumulated rainfall totals of up to 18 inches occurred in Southeast Louisiana and Mississippi and in Central and South Alabama. As a result, extensive flooding occurred throughout Central and Southeast Mississippi. Many locations in the Pearl and Pascagoula River Basins approached and broke their all-time record crests. The Leaf River at Hattiesburg crested at 31.53 feet breaking the record(which would later be broken again). Many locations in the Pascagoula Basin reached or exceeded their 50-year floods. In the Upper and Middle Pearl River Basin, flooding was not as extreme.

Another significant winter flooding event occurred in December 1982. Widespread flooding occurred in December 1982 in Central and Southern Mississippi. December of 1982 was a record month for almost every rain gauge in the state. Rainfall for the 6 month period from December 1982 to May of 1983 was in excess of 150 percent of normal across Mississippi.Heavy rainfall in December in the Upper and Lower Mississippi River Basin also produced a significant flood along the Mississippi River. For additional information on this event, please click here.

Flood Terms to Know

Flash Flood Watch	Flash Flood Warning	Flash Flood Emergency
Conditions are favorable in the atmosphere to where heavy rain could be possible over a specified area.	Flash flooding is occurring or imminent in the specified area. This can be from excessive rainfall or a dam or levee failure.	Extremely heavy rainfall has already occurred, will continue to occur, and emergency officials are reporting life threatening rises in water that are resulting in water rescues or evacuations.
Stay alert to the weather and think about where you would go if water begins to rise of you are put under a warning. Watch for development of heavy rain.	Move to higher ground immediately. Be on the lookout for water covered roadways.	Move to higher ground. Make sure to not cross water covered roadways or drive down roads that are barricaded due to high water.

Flood Safety Guidelines

If you are driving, look ahead and watch for flooding at highway dips, bridges, and low areas. Do not try to drive across water-filled areas of unknown depth. The road could be washed out.
Be especially cautious at night when it is harder to recognize flood dangers. Heavy rain events frequently and notoriously occur at night.
Do not camp or park your vehicle along streams or drainage areas particularly during threatening conditions.
Avoid already flooded and high velocity flow areas.
Do not attempt to cross a flowing stream on foot where water is above your ankles.

Flooding and Cars

Most deaths from flash flooding occur when vehicle operators drive their automobiles into flood waters of unknown depths only to find the water is deeper than they thought. At this point, the motor becomes inundated then stalls and the vehicle is soon swept away, taking the passengers with it. It does not matter how big the car is. It only takes TWO FEET of water to wash a car away. In addition, it only takes six inches of water to wash away a person. A simple rule to remember is Turn Around Don't Drown.