Assessment of Hydrologic and Hydrometeorological Operations and Services (1996) / Chapter Skim
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3 MODERNIZATION OF THE NATIONAL WEATHER SERVICE HYDROLOGIC SERVICES: AN EVALUATION
3 MODERNIZATION OF THE NATIONAL WEATHER SERVICE HYDROLOGIC SERVICES: AN EVALUATION
Pages 19-33
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From page 19... ...
This spatial and temporal distribution of precipitation is designed to serve as an input to continuous simulation hydrologic models. The NWS uses both rain gauge data and radar estimates of precipitation as inputs to a threestage precipitation processing system, or PPS (see Box 3-1~.
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From page 20... ...
Conclusion. Successful modernization of NWS hydrologic services depends on the ability of the NEXRAD network to provide accurate estimates of precipitation that benefit from improved spatial and temporal resolution.
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From page 21... ...
NEXRAD rainfall accumulation, determined at the highest resolution of the radar, represents an information data source that would permit the issuance of timely flood warnings in very small basins. The committee understands that, in software Build-9, the NWS plans to produce all graphical NEXRAD precipitation products in a polar coordinate format and to add a digital hybrid reflectivity product with high resolution.
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From page 22... ...
Surface-Observing Networks Surface-water observations are made by stream gauges that measure water level in rivers, streams, lakes, and reservoirs and by precipitation gauges that measure rainfall and the water equivalent of frozen precipitation (snow, hail, etc.. Both stream and rain gauge data are critical sources of input data for NWS hydrologic models.
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From page 23... ...
Issues associated with the rain gauge network are related not to any decrease in the number of rain gauge locations, but to the quality of data from cooperative networks, the availability of rain gauge data in real time, the geographic distribution of rain gauges, and the temporary loss of accurate precipitation data from locations where the ASOS is used to obtain local climatological data. In turn, the latter issue impacts the continuity and accuracy of the historical precipitation record.
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From page 24... ...
Given the spatial distribution of the cooperative observer network nationwide, upgrading all nonrecording rain gauges in the network with rain gauges that can be automated and equipping all existing automated weighing rain gauges in the network with satellite, phone, or radio interrogation capabilities would greatly facilitate NEXRAD precipitation processing. A continual effort must be exerted by the NWS to ensure the flow of rain gauge reports for use both in the calibration of precipitation estimates from NEXRAD and in the generation of river forecasts from hydrologic models.
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From page 25... ...
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From page 26... ...
For example, digital precipitation estimates produced by NEXRAD with high spatial resolution indeed represent a breakthrough for hydrologic operations that heretofore relied on point rain gauge observations. Furthermore, highresolution (3-arcsec, or less than 90-m)
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From page 27... ...
The WFO forecaster issues flash flood warnings and watches by comparing the observed or forecasted precipitation amounts with the guidance values present in the flash flood guidance. This task is performed with the WFO Hydrologic Forecast System (WHFS)
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From page 28... ...
The number of service hydrologists should be increased so that each WFO has a program leader for WFO hydrologic operations, at least for the first year or two following implementation of the AWIPS at each field office. The full capabilities of the WHFS can be realized only after WFO staff are adequately prepared to deal with hydrologic forecasting during flood-water crises and severe weather conditions.
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From page 29... ...
OPERATIONS Recognizing the complexity of and urgent demand for hydrologic forecasts to meet growing societal needs, the NWS has chosen to integrate its operational missions in 9"0pen-loop" behavior refers to the use of a model to simulate long-range conditions without any correction of its forecasts (through updating the model-state variables and parameters)
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From page 30... ...
Another concern is that river basins have been apportioned among the various WFOs according to geopolitical boundaries rather than physiographic boundaries.l° This apportionment will cause confusion among those users who do not know where to acquire hydrologic forecasts and warnings for their area. NWS field personnel are also concerned about their ability to maintain continuity and consistency in hydrologic forecast and guidance products because hydrologic service areas of responsibility are no longer coincident with county warning areas of responsibility.
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From page 31... ...
The current system fails to archive and efficiently retrieve most of the data that will be needed for twenty-first century improvements in NWS hydrology. These data include: · the hourly precipitation summaries from Stage II and Stage III processing of NEXRAD data · rain gauge and stream gauge observations used to calibrate NEXRAD precipitation patterns or to calibrate and validate hydrologic forecast models · daily knowledge of basin characteristics such as vegetation indices, antecedent moisture conditions, and major construction · stage-discharge rating curves that relate flow volumes to stream gauge readings 31 · records of previous stream flows documented on up-todate E-l9 forms of the NWS The NOAA Hydrologic Data System, now under development (NWS, 1996b)
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From page 32... ...
These data include information from automatic and manual sources such as stream gauges, precipitation gauges, cooperative observers, flood warning systems, satellite-relayed data, telemetered data and, most important, data from the NEXRAD network. Satellite precipitation estimates can contribute useful hydrologic information in some areas.
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From page 33... ...
Several individuals felt that external users had only a minimal impact in defining new hydrologic services. At the same time, these field hydrologists emphasized the importance of being in the pipeline of hydrologic information produced by other federal agencies so as to minimize miscommunication during critical, shortfused events.
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