Thursday, July 8, 1999 | 11:16 a.m.
Massive black clouds tower over the Las Vegas Valley. Thunder crackles in the hot still air, followed by sheets of water that catch desert dwellers in water over their ankles in minutes.
The National Weather Service sends out warnings, but by then it may be too late. Dry washes overflow with torrents and an unsuspecting motorist may already be caught in a flash flood.
Local weather experts now have technology that will get the word out faster -- crucial minutes that they believe can help save lives.
In Southern Nevada flooding comes suddenly, often without warning as residents and visitors drive their cars or four-wheel-drive vehicles across the valley.
"It can be dry and sunny on one side of the valley and pouring enough to flood homes and streets on the other," Chief Meteorologist Larry Jensen said.
Mid-July is the beginning of what weather service meteorologists call Southern Nevada's monsoon season, at least two months of fierce summer storms, each one bringing with it the danger of flash floods.
The monsoon season is sparked by a flow of warm, moist air from Mexico which then collides with a high-pressure system over the Four Corners and a low-pressure system over Southern Nevada. When the the three air masses run into each other, thunderstorms are formed in the Las Vegas Valley.
Floods have been recorded in Southern Nevada for almost 100 years. The U.S. Soil Conservation Service has documented 184 different floods in Clark County this century. And while July and August see most of them, every month has at least one flood recorded in some year.
Since 1960 the area has experienced eight "million-dollar floods," meaning property damage was valued above $1 million.
Even newcomers to the valley can recall destructive storms such as last September's thunderstorm over the southeastern valley that spawned a tornado that damaged two buildings in Henderson.
But desert flooding can be deadly too. In the past 25 years, 24 people have died in Southern Nevada torrents.
Among them was former Teamster Union executive Harold "Mel" Dittmer, 58, who drowned Aug. 10, 1998, when he tried to cross Skyline Road and Tamarack Drive in Henderson and was knocked down by the rushing waters.
Quicker warning
When black clouds tower above the mountains south and west of Las Vegas, the National Weather Service gets ready to warn residents of accompanying lightning, heavy rains and flooding.
This year the warning system will be quicker, thanks to new technology.
Local meteorologists have added modern computers and radar linked with other stations around the West to get the latest information.
Just a few months ago, several forecasters had to calculate the speed, direction and size of a major summer storm by hand using information gleaned from several computer tracking systems, Kim Runk, National Weather Service science and operations officer said. It took up to six minutes.
A high-speed computer called an Advanced Weather Interactive Processing System, installed in February, allows a meteorologist to follow the speed, direction, severity, rainfall and lightning in a storm that roars into the valley on a single computer screen.
Now one forecaster can see a storm's path and issue a warning in one minute. From the forecaster's office, the word is sent out via local television, radio and the Weather Channel.
Flood control
Protecting those in the path of a storm or a flood is a recent development for Clark County. Since 1989 Southern Nevada residents and visitors have paid an extra quarter-cent in sales taxes to build flood controls for the valley. To date officials have spent $300 million on 20 major flood-control projects, Regional Flood Control District Director Gale Fraser said.
Most of the money has been poured into building detention basins near Red Rock Canyon, Las Vegas Creek, which runs along Washington Avenue, and in Henderson to prevent runoff from the mountains flooding the rapidly growing residential areas.
While 12 square miles of the Las Vegas urban area is considered protected from flooding, there is much more work -- at least 30 years of it -- to flood-proof the area, Fraser said.
If heavy rain falls in the center of the valley, there is little protection from floodwaters filling the Charleston Boulevard underpass or the intersection at Oakey Boulevard and Western Avenue, for example.
In the next year the Regional Flood Control District and Clark County will begin or finish $200 million in new flood control projects, Fraser said. The County Commission approved $150 million in bonds for these projects in October. Developers, cities and the county contribute the rest of the funds.
Danger still
Even with the flood controls being built, as Southern Nevada continues to grow, residents need to learn about the dangers posed by summer thunderstorms and accompanying flash floods, Fraser said. Typically, the flooding lasts a few hours. In 1984 flooding lasted for weeks across the valley.
The natural shape of the valley -- it's more like a funnel than it appears -- combined with the increasing number of paved areas add to the damage that flood waters can cause, Fraser said.
Water raging through Henderson and Boulder City two years ago was clocked at 30 mph. "Who in their right mind would stand in front of a car going 30 mph?" Fraser asked. Yet people think nothing about trying to wade across a road that has turned into a raging river.
Water running to the top of the curb in a local street can kill. "Remember, 6 inches of running water can knock a full grown man down and 2 feet of rushing water can move a car," Fraser said, recalling Dittmer's death.
What's the best advice for those caught in a Southern Nevada thunderstorm? According to Fraser: "Avoid moving water. Period."
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