Remembering the Great Flood of 1993: River Forecasting, Then and Now (148)

Mark Fuchs, National Weather Service, Weather Forecast Office St. Louis, MO, St. Charles, MO

Steven Buan, National Weather Service, North Central River Forecast Center

Michael DeWeese, National Weather Service, North Central River Forecast Center

A. Juliann Meyer, National Weather Service, Missouri Basin River Forecast Center

 

Abstract:

Remembering the Great Flood of 1993: River Forecasting, Then and Now

Mark C. Fuchs

NOAA/NWS, St. Charles, MO

Steven D. Buan and Michael M. DeWeese

NOAA/NWS/NCRFC, Chanhassen, MN

A. Juliann Meyer

NOAA/NWS/MBRFC, Pleasant Hill, MO

This presentation commemorates the 25th anniversary of the Great Flood of 1993, reviewing the data processing and river modeling employed at the time, then comparing these methods with the data processing and modeling used today. During the prolonged and historic flooding event of 1993, the Missouri Basin River Forecast Center (MBRFC), the river forecast center responsible for generating river forecast guidance for the Missouri River basin, utilized the modelling framework called RIV-ALL, a framework encompassing all of the basic programs necessary to generate river forecasts. This framework used the antecedent precipitation index (API), to convert rainfall into runoff. This was an event-oriented model which did not employ forecast precipitation into its calculations. While the model could operate on a 6-hour time step, most larger streams were modelled using a 12 or even 24-hour time step. The output was similarly coarse, with only one forecast value per day generated out to just 3 days. Data processing of river and rainfall observations was also sporadic. While data collection platforms (DCPs) at river gages did transmit automated river stage and precipitation readings at several sites along the Missouri and Mississippi rivers, many other river sites required manual readings that were typically limited to no more than one or two readings a day. At the North Central River Forecast Center, the river forecast center responsible for generating river forecast guidance for the upper Mississippi River basin down to Chester, Illinois, the National Weather Service River Forecast System was used as a new modelling framework. However, the API model was also used for rainfall to runoff calculations. Similar to MBRFC, a 12 or 24-hour time step was common in this modelling environment, and no forecast precipitation was utilized.

Today, both RFCs employ modeling within the framework of the Community Hydrologic Prediction System, which uses a variety of available models, including the more robust Sacramento Soil Moisture Accounting Model for rainfall to runoff calculations. This modelling is performed on a 6-hour time step, and can use time steps as short as 1-hour. This framework also uses forecast precipitation as far into the future as the user deems appropriate. Operationally, 24 hours forecast precipitation is used during the warm season, and 48 hours during the cool season, though these limits can be expanded based on regional confidence in each event. Satellite-transmitted river and rainfall data from DCPs are much more common throughout both the Missouri and Mississippi river basins as model input. Forecast output is generated every six hours from 5 days to several weeks.