Jed Boal ReportingAs flood watch intensifies many Utah communities anxiously watch the forecasts to see what the rivers will do. The science of flood forecasting has come a long way in recent years.
Right now City Creek in Salt Lake is flowing at 71 cubic feet per second and it's 1.7 feet deep. By Monday at this time it's forecast to rise to bankfull.
How do we know? When the Sevier River breached its banks this week it did not surprise those who study the streams.
Len Randolph, KSL-TV5 Meteorologist: "The advanced hydrologic prediction service is superb."
KSL-TV5 Meteorologist Len Randloph says the where and when of flooding has improved dramatically in 20 years. Not that long ago forecasters had to be in the field to take measurements.
Len Randolph: "Now with the internet and these computers we have, you can sit at a desk and see the flow from the smallest ditch or canal to the biggest reservoir. It's all at your fingertip."
National Weather Service Hydrologist Brian McInerney works with an experienced staff to put out forecasts.
Brian McInerney, National Weather Service Hydrologist: "It's a combination of a lot of factors and so far it seems to be working out quite well."
The forecast starts in the fall. Spring run-off depends on the saturation of the soil after fall rains. In the winter the Natural Resources Conservation Service monitors snow depth and water content across the state. Spring climate is the final factor -- heavy rainfall increases the flow, so do high temperatures.
The USGS records stream flows with gauges across the state.
Brian McInerney: "We're doing that basically on a 24-hour, seven day a week work schedule to get this run-off correct."
Hydrologists have created models for snowmelt with mathematical equations. Years ago the equations were rough. Today the National Weather Service has computer power and experienced forecasters who can adjust the models as they need.
"It goes into all of the river basins and measures the flow and how high the water is in all of those channels."
Flooding aggravated by a rain storm is much tougher to forecast. Right now the forecasting is all tied to the hot air and a lot of snow.