High-tech forecasting for Howard Hanson Dam

SEATTLE - At the National Weather Service forecasting office on Lake Washington, Ted Buehner watches the weather profile at Westport along Washington's coast.

The data comes in from an elaborate and portable weather station put online just days ago. There's so much stuff in this weather station, it rides on a flatbed semi-trailer. And what it does is tell forecasters how much rain is coming in off the Pacific Ocean that could hit the Central Cascades and the watershed that leads into reservoir behind the compromised Howard Hanson Dam.

The U.S. Army Corps of Engineers has been trying to shore up what's known as the right abutment to the dam - a collection of rock and debris left over from an ancient landslide that one side of the dam is braced against. It's this part of the overall dam structure that's leaking causing engineers lengthy bouts of heartburn trying to decipher as to why. A temporary fix designed to slow down the loss of water is in place, but we won't know until later this week how effective the Corps thinks it will be.

The bottom line is that the Corps may have to allow enough water down into the Green River to protect the dam and its weakened abutment, but flood downstream communities at the same time.

Those communities including Auburn, Kent, Tukwila, Renton and portions of unincorporated King County are bracing for that, and along with reinforcement of levees and plenty of sandbags have been trying to prepare while hoping the worst-case scenarios don't come true.

But part of that reinforcement comes from the Weather Service, which in the next few weeks will add more wind profilers and vertical radars that can analyze the water content of incoming storms.

Some of these devices are being installed in Tacoma and at the dam itself, but some are as simple as adding and upgrading rain gages to send real-time information about how much water is being collected.

A lot of it is going to be considered "ground truth" - how much rain has fallen on the ground, how much water is moving downstream, and all that is going into the short term of how the river is going to behave, says Buehner.