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Hydrology Laboratory
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Presented at AMS Conference
12th International Conference on Interactive Information and Processing System (IIPS) for Meteorology, Oceanography, and Hydrology
Atlanta, Georgia
January 28-February 2, 1996


Office of Hydrology
NOAA/National Weather Service
1325 East-West Highway
Silver Spring, Maryland 20910

North Central River Forecast Center
NOAA/National Weather Service
1733 Lake Drive West
Chanhassen, Minnesota 55317-8581


The United States Department of Commerce , National Oceanic and Atmospheric Administration (NOAA) , National Weather Service (NWS) , has the responsibility to provide river and flood forecasts and warnings for the protection of life and property within the United States. These forecast services also provide for economic and environmental well-being through improved water resources management. The continuation and advancement of these services is occurring through NOAA's Advanced Hydrologic Prediction System (AHPS) .


The deaths and economic losses resulting from The Great Flood of 1993 and our Nation's subsequent floods and droughts have forced the need for improved predictions to support flood/drought management and damage mitigation. Furthermore, the allocation of water among competing demands (i.e., fisheries, irrigation, hydropower and municipalities) looms as a national problem that requires improved water quantity forecasts for sustainable use. AHPS products with extended forecast lead times (up to several months) will greatly improve the Nation's capability to take timely and effective actions that will significantly mitigate the impact of major floods and droughts. The system will also provide products to water resource managers for the evaluation of water availability and allocation for water supply, navigation, hydropower, ecosystems and agriculture.


National Weather Service (NWS) River Forecast Centers (RFCs) typically issue stage forecasts for only 1, 2, and 3 days into the future at most forecast points and crest forecasts out to about 1 week for a few selected forecast points. The NOAA "National Disaster Survey Report: The Great Flood of 1993" (NWS, 1994) reports that federal, state, and local groups have a need for advanced hydrometeorologic/hydrologic forecast products with increased lead-times. Many of these groups express the need for a range of forecast stages with associated probabilities of occurrence. Similarly, during the widespread drought which affected most of the country in the mid-1980's, people were asking for hydrologic forecast information that was not available. During these events, agriculture, navigation, and water supply problems amassed damages in the billions of dollars. AHPS advanced hydrologic forecast products, with extended forecast lead-times, will greatly improve the capability of emergency managers to take timely and effective actions that will significantly mitigate the impact of major floods and droughts.

3.1 AHPS Defined

AHPS is a critical component of an Advanced Hydrologic Prediction System (AHPS; Fread, 1995) which builds upon the following:

    (1) partnerships with other water cooperators (federal, state, multistate, quasi-governmental, and private sector organizations);

    (2) the NWS infrastructure including the 13 RFCs and the NWS River Forecast System (NWSRFS) , a very large software system used by RFC hydrologists to produce forecasts of time series of discharges or stages at selected locations (approximately 4,000 along the Nation's rivers); and

    (3) the NWS Modernization which is providing NWS River Forecast Centers (RFC) with Advanced Weather Interactive Processing System (AWIPS) equipment, a powerful suite of networked computer workstations with graphic capabilities.

The modernization is also providing national coverage with approximately 140 WSR-88D Doppler Radar radars which produce multisensor, high resolution (space and time) precipitation estimates utilizing gauge precipitation observations from networks such as the new Automated Surface Observing System (ASOS) . The precipitation processing algorithms are being enhanced to account for bright band effects and to improve the rain gauge bias adjustment, while future enhancements will address orographic effects and snow accumulation.

AHPS provides the pathway to:

    (1) make critical software enhancements to the NWSRFS;

    (2) develop a NOAA Hydrologic Data System (NHDS) ;

    (3) increase the use of short- to long-range weather and climate forecasts within the NWSRFS through appropriate hydrometeorological coupling algorithms;

    (4) effectively calibrate and field-implement the advanced hydrologic/hydraulic models within the NWSRFS;

    (5) implement a Snow Estimation and Updating System (SEUS) which provides gridded estimates of snow water equivalent; and

    (6) provide more timely, accurate, and informative forecast products (e.g., Figure 1) to government and quasi-government water and emergency managers and to private sector intermediaries who provide value-added services to specific industries.

Figure 1. Long-term probabilistic forecast of river stage

3.2 AHPS Implementation

During fiscal year 1995, NOAA began AHPS implementation activities within the upper Mississippi River basin through a significant commitment by personnel of the North Central River Forecast Center (NCRFC), the Regional Hydrologist and other staff of the NWS Central Region , and the NWS Office of Hydrology . AHPS short-term implementation goal is to demonstrate an operational long-term probabilistic forecast system for the Des Moines River basin by the Spring of 1997. AHPS functionality and associated implementation activities at the NCRFC include:

    Provide advanced hydrometeorologic/hydrologic modeling procedures that better account for the natural and man-made complexities of the nation's river basins;

    Implement dynamic streamflow modeling in river reaches with significant dynamic effects caused by backwater, levee overtopping, or other transient phenomena;

    Implement the Extended Streamflow Prediction (ESP) procedure in order to provide probabilistic hydrologic forecasts into the future from weeks to months (e.g., Figure 1);

    Include the effect of reservoir operations in both short-term and long-term forecasts;

    Couple meteorologic forecasts at all time scales within the Extended Streamflow Prediction (ESP) procedure; and,

    Provide advanced products (e.g., probability of occurrence information) for water resources management activities to other federal, state and local organizations.

Once AHPS has been implemented for the Des Moines River basin, activities for its implementation in other NCRFC basins will occur. As an increase in resources become available, AHPS implementation can be expedited within the Mississippi Basin as well as early implementation in one or more additional basins in the United States, e.g. the Columbia River Basin which is of critical economic and environmental importance to the Nation.


Coordination among individual Weather Service Forecast Offices (WSFO)/Weather Service Offices (WSO), RFC's, national centers, and regional and national headquarters is a vital part of the warning process. As the NWS issues forecasts and warnings, those products are distributed in near real-time to a wide variety of other federal, state, and local agencies. In the Modernized NWS, this internal coordination and product dissemination will be enhanced, in part, through the application of advanced hydrologic forecast products.

4.1 Today's Hydrologic Forecasting

The magnitude and duration of the Great Flood of 1993 (NWS, 1994) placed enormous stress on the forecast system infrastructure and NWS forecasters. Given the system's limitations and the resources available during that event, the forecasts and warnings were incredibly good. For example, at the peak of the flood along a stretch of the Mississippi River near Hannibal, Missouri , approximately 50 percent of the estimated 4 million gallons of water per second was flowing outside the "main channel" of the river and behind the levee systems. In spite of these complex hydraulic conditions, the NCRFC provided forecasts for the city of Hannibal that were sufficiently accurate and timely to allow the U.S. Army Corps of Engineers (USACE) and the city of Hannibal to take action to reinforce the major levee system protecting the city. Although numerous anecdotes of major mitigation actions can be cited, there are still substantial opportunities for improvements that will provide significant benefits during future flood events and pay even larger dividends to the Nation.

Today's River Forecast Centers (RFC) typically make river forecasts on a mainframe computer at the NOAA Central Computer Facility (NCCF) in Suitland, Maryland. Input information is prepared at each RFC and submitted via phone lines for batch processing at the NCCF. Once the batch job is executed, model output is returned via phone lines to the RFC and the forecaster must examine forecast output on large amounts of printer paper or, in the case in the NCRFC, on a monitor. The forecast process is slowed by the long the turnaround time for the model runs and by this outdated output format. Next, if the forecaster determines that data-input or model states need to be updated, it is a time-consuming process to format the input necessary to make the changes, resubmit the job to the NCCF, wait for the results, and work through a second pile of line-printer output. The long range forecast process is even more inflexible. Clearly, a cumbersome forecast process adds unnecessary stress to forecast periods of critical need. Implementation of AHPS will streamline RFC operations.

4.2 AHPS Services

AHPS implementation will greatly improve the Nation's capability to take timely and effective actions by providing new tools to forecasters and new forecast products to cooperators and the public. AHPS will develop approaches to package and disseminate advanced graphical and digital products that will convey more information with greater clarity than the short term single value stage forecasts which are currently the norm for river forecasts.

A baseline product packaging development task is to work with potential users in order to develop types of products needed. As the NWS issues forecast and warning products, they are distributed in near real-time to a wide variety of other federal, state, and local agencies. Major cooperating agencies include the Federal Emergency Management Agency (FEMA), the USACE, and local and state emergency management agencies, to the media and to the general public.

In most cases during the Great Flood of 1993, these coordination activities were effective. However, in the future cooperating agency personnel have requested that during such extreme events, interagency communication could be enhanced by on-site NWS personnel being available to provide rapid, clear interpretation of the NWS forecasts and warnings.

Similarly, during the Great Flood, the media were highly complimentary of NWS cooperation and the high quality of the information the NWS provided. To help broadcasters meet public demand for early, daily information, members of the media requested that the river stage information and flood forecast product issuance be coordinated with broadcast schedules. Radio and television broadcasters would then be able to tailor products for specific audiences. The AHPS initiative will address these coordination issues by providing a framework for cooperation and by providing advanced forecast products.

4.3 Tomorrow's Products

For the AHPS program, new types of products based on probabalistic forecasting techniques are being investigated and new software to conveniently generate those products are being developed. The AHPS short-term design features include probabalistic long-range outlook hydrographs for stage, discharge and flow volume that have accompanying indicators of uncertainty (e.g. figure 1). Long-term design features include gridded estimates of snow-water equivalent, soil moisture and flash flood guidance, and probabalistic flood inundation mapping capabilities (e.g. figure 2).

Figure 2. Flooded area map, providing inundation depth information using real-time or advanced hydrologic forecast data for a future time window

Probabalistic forecasts are generated from analyses of the NWSRFS ESP function time series traces. At this time, that analysis is completed when the traces are generated which makes the system inflexible. AHPS implementation will provide forecasters with a new software tool called the ESP Analysis and Display Program (ESPADP). ESPADP will enhance the forecasts in several ways. First the ease with which the analysis can be accomplished will lead to greater of use of the ESP forecasting technique. Second, by providing a variety of interactive graphical displays the forecaster will be able to understand more easily and more completely the probabilities generated by an ESP forecast. Finally, by providing more attractive and easily read graphical products NWS cooperators will find it easier to use forecast products.

With the added flexibility and graphical displays available through this modernized software, a variety of enhanced forecast products can be generated by the RFC's. Investigations into possible products are underway to asses cooperator interest and system development including data input, data storage, software design and product formats. For example, several end users of NWS long range stage forecasts have requested that NMC long lead meteorological outlooks be included in these long range stage forecasts. Inclusion of such forecasts requires the development of new scientific algorithms, the definition of new input data streams, new data storage facilities and the development of appropriate displays of the forecast data. The AHPS program has provided the impetus for such improvements.

One enhanced product that will be available for the AHPS demonstration project on the Des Moines Basin in the spring of 1997 will be probabalistic hydrographs (see figure 1). This type of forecast that would have been useful for disaster managers during the Great Flood of 1993. With this type product, forecasts with explicit probabilities, or confidence bands, will convey to the end-user the confidence, or level of certainty, that the forecaster has in any specific forecasts. In this way, modernized hydrologic forecast products will provide not only the forecaster with a mechanism to impart more hydrologic forecast information to the end-user but also will provide more information to the end-user to construct a risk analysis for alternative hydrologic scenarios. This new product is a huge step forward from the previous ESP output format. Where in the past the forecaster was forced to review tabular output for a limited period, he or she will be able to review the expected flows over a range of forecast periods. In addition, it will be possible to pass the graphical displays on to the end users directly, thus enhancing their understanding of the state of the hydrologic system.

Coupled with the ESPADP software will be utilities that permit the user to verify the effectiveness of their forecast over selected periods in the past. Such verifications will generated with the forecasts and will be useful for managers as they integrate a multitude of pieces of information into a single decision.

Two long-term goals of the AHPS project are to develop the capability to generate inundation maps (see figure 2) based on the probabalistic stage forecasts, and second to provide gridded estimates of a variety of state variables describing the hydrologic system. The goal of inundation mapping will be to provide local emergency managers a clear definition of the areas that are likely to experience flooding. By coupling the mapped areas with probabalistic forecasts, emergency managers will be able to evaluate the importance of evacuating specific areas. The translation of the forecast river stage to actual locations on the ground will be more readily communicated with these types of inundation maps.

Gridded estimates of hydrologic variables will provide forecasters and users with an in depth view of the natural system. Gridded estimates of the snow cover, and soil moisture, will enable forecasters and managers to evaluate the probability of flooding, and in more localized areas.


NOAA has the national responsibility to provide river and flood forecasts and warnings for the protection of life and property and for the economic and environmental well-being of the Nation. The advanced hydrometeorological modeling provided by AHPS will greatly improve NOAA's capability to provide more timely and accurate forecasts. For these multiple uses of AHPS advanced forecasts, NOAA will provide advanced products which meet multiple objectives through the most effective means available.

The operational AHPS, along with these advanced products, will contribute to DOC's leadership role in fostering economic gains for environmentally sound decision making. AHPS is a focused program of the President's National Science and Technology Council (NSTC) Committee on Environment and Natural Resources (CENR) and one of DOC's highlighted programs contributing toward sustainable use.


Fread, Danny L., June 1995: A Pathway Toward Improving Hydrologic Predictions. Iowa Hydraulics Colloquium Issues and Directions in Hydraulics, 5 Pages. NWS, February 1994:

Natural Disaster Survey Report, The Great Flood of 1993, NOAA Natural Disaster Survey Report. U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Weather Service, Office of Hydrology.

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