Stair-stepping the river crest

More than two decades ago, when I was the chief of forecast operations at the Indianapolis Weather Service Office, we were wrestling with the challenges presented by predicting the crest along major rivers. For the most part, we dealt with early spring snow melt combined with observed rainfall, as well as the impact of ice jams.

Rises on the river were based on observed stages, antecedent conditions,(i.e. soil moisture), temperature forecasts, the time of year and reported rainfall.. The river forecast models would ingest observed 24 hour rainfall, averaged over the basins, forecast the flow along the tributaries and then forecast the rise and fall at specific locations for the next five days.

Unfortunately, in the 1980s we had yet to boldly accept the challenge to attempt to incorporate what is now known as quantitative precipitation forecast, or QPF.

Currently skilled hydrologists and meteorologists in NOAA's River Centers and local offices are adding this additional forecast information. Daily computer model runs are adjusting the crest forecast based on anticipated rainfall, averaged across the basin for the next seven days.

River stage forecasts. Click on a yellow colored site.

These critical forecasts of quantitative precipitation help to keep the stair-stepping appearance to a minimum, since forecasters are now adding expected additional rainfall, not just observed rainfall. In the 80s, we often knew the river could continue to rise higher if more rain occurred. So a forecast crest of 15.5 feet might step up to 16.0 feet if rain fell in the basin while the river had yet to crest.

You can follow along on the river crest forecast on the National Weather Service River Forecast link. It may be of interest with the periods of wet weather expected in the next three to four days.

Quantitative precipitation forecast for the next three days.

CE