11 June 2010

16 Dead in Arkansas Flash Flood (Updated)

Posted by Dan Satterfield

Digital rainfall estimation off of the Doppler Radar in Little Rock, Arkansas. Nearly 20cm (8 inches) of rain fell overnight in the Ouachita National Forest.

There are many similarities to the flash flood that hit Montgomery County, Arkansas last night and the Big Thompson Canyon flood in Colorado in 1976. Both were National Forest campgrounds near streams. 145 campers died on 31 July in 1976 in the Colorado flood. The death toll now stands at 16 in Arkansas.  Some are still missing.

IR satellite image at 12:45 AM Friday showing the MCS over SW Arkansas. The heavy rain lasted for nearly 5 hours. The dark purple indicates clouds with a temp. of -70C. Clouds that cold would be very high (Over 50,000 feet.)

What Caused It

The flood was caused by what meteorologists call an MCS.

MCS stands for Mesoscale Convective System. In other words, a big cluster of thunderstorms. These systems can produce heavy rains as thunderstorms redevelop over the same place for hours. Last night the winds aloft that steer the storms were very light and this contributed to the heavy rainfall.

The MCS was kicked off by a very slow moving upper level low that has been drifting northeast across Texas for the past few days. It moved into Arkansas last night. A flood  gauge near the campground showed a rise in the river of 2.4 meters in one hour! The total rainfall is nearly 20cm or around 7.5 inches of rain.

It’s Happened Before

I was working on-air in Tulsa, Oklahoma during one of these events.  It was Memorial Day weekend in 1984. That night is burned in my memory. That flash flood killed 14 people.

These events are why you should always have a weather radio with you when camping. There are some excellent and inexpensive models available now.

Stream discharge from a river gauge near the campground. (USGS)

Budget Cuts May Impair Warnings

Another part to this story is the flood gauges on rivers. Most of these are put in place by the USGS. Budget cuts are forcing the removal of many of them.  This means there will be fewer gauges that forecasters can rely on to issue short fused warnings. Some gauges with many years of data will no longer be maintained.

Here is a stream gauge near the site of the deadly flood. The stream discharge triples in just a few hours!

The public is always worried about getting hit by a tornado when in reality the main weather killers in America are lightning and flash floods.

A Climate Connection?

One last thing.

If someone tells you this was caused by climate change they are wrong. If someone tells you this was NOT caused by climate change they are also wrong. The atmosphere is holding more water vapor now than it did 40 years ago. What you can say is that as the planet gets warmer, we will likely see heavier and more frequent extreme rainfall events.

Like this one.

Would it have happened anyhow? Possibly. No one can say for sure about any one event.