NWS to offer long-term forecasts

The National Weather Service is developing a new system that for the first time will provide long-term river forecasts to better predict the probability of floods and droughts.

The Advanced Hydrologic Prediction System (AHPS) will rely on advanced modeling to produce flood and drought forecasts that cover several months. Forecasts typically cover only a few days.

The longer-range forecasts will improve the ability of emergency managers to prepare for the impact of major floods and droughts. The system also will allow water resource managers to better evaluate water availability for water supplies navigation and agriculture.

During the last decade severe droughts and floods have increased the need for more advanced forecast products. "In the mid-1980s people were asking `When will the drought end? When can I irrigate my crops? When will barge traffic start? "' said John Ingram a hydrologist and AHPS program leader at NWS. "They were asking similar questions during the great flood of 1993."

While the 1993 flood which inundated communities and farm land along the Mississippi River "doesn't happen every day the probability that it could happen [next] summer is still there " Ingram said.

AHPS will expand NWS' River Forecast System which the 13 regional River Forecast Centers use to predict floods. It also will work with systems in NWS' modernization program including the Advanced Weather Interactive Processing System (AWIPS) and Doppler radar data as well as advances in NWS weather and climate forecasting capabilities. AWIPS integrates and displays satellite radar and sensor data into one system.

"AHPS is going to create a whole new suite of products " said Dean Braatz the hydrologist in charge of the North Central River Forecast Center (NCRFC) Minn. For example NWS is investigating new types of products based upon forecasting techniques using probability theory and is developing new software to generate those products.

One enhanced product will be probability-based hydrographs which are graphs that depict the long-range outlook for a river's stage discharge and flow volume. In the past forecasters reviewed tabular output that covered only a limited period and issued forecasts good for only a few days. The new hydrographs will be passed directly to end users.

NWS will add other features later including estimates of snow-water levels soil moisture and flash-flood guidance along with probabilistic maps of flooded areas.

The model AHPS will be operational by spring and will support the Des Moines River basin Braatz said. NWS then will expand the system to support the Mississippi River basin and possibly the Columbia River basin.Initially AHPS will be installed on the pre-AWIPS system that the NCRFC is using. Software will be ported over to the new AWIPS system when it is installed sometime next summer Braatz said.

NWS will conduct a separate solicitation for AHPS software development and implementation. Proposals are due this week for the task-order contract to provide assistance with the scientific issues related to hydrologic models such as calibration modeling. Federal Sources Inc. McLean Va. estimates that contract to be worth more than $6 million.


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