From the beginning of April through the end of May, a team of hydrologists at the National Weather Service's Salt Lake City office turns flood forecasting into a 24-hour, seven-days-a-week occupation.

Given the huge snowpack in the northern Utah mountains and what looks like, finally, the arrival of genuine spring weather, the place has already begun to jump - and will only get busier as the temperatures climb and the region's rivers and streams swell to the brim, and beyond. Forecasters are calling this spring the most active for potential flooding along the Wasatch Front since 1997.

"It's just starting to roll," hydrologist Brian McInerney said Thursday at the Weather Service office, located near Salt Lake City International Airport. "The scenario we're looking at now is shaping up as a six-week event, and possibly longer, depending on the climate."

McInerney is the public face of flood forecasting in Utah, the Weather Service's go-to guy for the news media and state and local government agencies. His job: to get the word out when flooding looms.

But McInerney gets his data from the Colorado River Basin Forecast Center, which is located in the same office and delivers long-range water supply and flood forecasts to seven Western states. Number crunchers supreme, the center's hydrologists process hundreds of thousands of pieces of data and translate them into flood probability forecasts - which are in turn used by federal, state, county and city agencies, as well as businesses and homeowners.

"We're set up to go 24 hours a day. And if things get crazy, we'll extend the shifts," said hydrologist Greg Smith, whose own personal on-duty record is 22 straight hours during one particularly active flood season.

Forecasters likely will log some long hours this spring. The top of City Creek Canyon, regarded as a lower-elevation snowpack location, is currently 200 percent of normal and water has only begun to rumble down. A similar scenario is unfolding at the top of Mill Creek and Big and Little Cottonwood canyons, which are all at least 150 percent of normal and sport even bigger snowpacks. May is shaping up as a very interesting month, especially if temperatures spike, as they did during the record flood season of 1983.

Colorado River Basin Center forecasters use multiple sources to create their flood models, converging precipitation, snowpack, river and reservoir data that is largely furnished by other agencies - such as the Natural Resources Conservation Service, which provides snow totals, or the U.S. Geological Survey, which furnishes stage and volume numbers for rivers and streams.

Most of this data collection is high-tech in nature, but the National Weather Service also still does it the old-fashioned way, relying on observers to phone or e-mail data in from remote outposts, or roving spotters to simply call in what they see.

"Everybody has a certain niche that we pool together to create a forecast," says McInerney.

Weather being what it is, forecasters also have to be able to make adjustments on the fly. When that unforeseen lake effect storm hits or temperatures climb higher than expected, the new numbers have to be poured into the models - which all incorporate historical climate and precipitation conditions. In this way, forecasters can quickly, and usually accurately, make their flood calls.

This wasn't always the case. Even a decade ago, computer technology was unable to furnish such fast answers to changing conditions, says Michelle Schmidt, chief hydrologist at the Salt Lake City office of the National Weather Service.

"We've gotten pretty good at forecasting river levels," she said.

Nor was the Internet developed to the extent that it could deliver one-stop shopping for consumers. Today, both the National Weather Service and the Colorado River Basin Forecast Center Web sites provide more information than even the hungriest weather junkie can consume in one sitting.

That, in the end, is what this forecasting business is all about, says Larry Dunn, chief meteorologist of the Salt Lake office. And during flood season, it takes on an urgent tone.

"We spend a lot of time with the emergency management agencies," he said. "Brian's been working for months with these people as we've watched the snowpack develop. And if weather occurs that could cause property damage or endanger lives, they'll be ready."

jbaird@sltrib.com

Forecasts online

For flood forecasts and stream information, go to:

The National Weather Service Salt Lake City Web site: http://www.wrh.noaa.gov/slc

Also, visit the Colorado River Basin Forecast Center at http://www.cbrfc.noaa.gov