Completing the Forecast Characterizing and Communicating Uncertainty for Better Decisions Using Weather and Climate Forecasts (2006) / Chapter Skim
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3 Estimating and Validating Uncertainty
3 Estimating and Validating Uncertainty
Pages 39-65
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From page 39... ...
In this report, the term "objective probabilistic forecast" is used through improved numerics and physics parameterizations, to mean estimates of stable frequencies derived using statistical theory, measurements, and model forecasts. The committee's use of the term "objective probability forecast" should not be confused with the common 2http://www.emc.ncep.noaa.gov/.
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From page 40... ...
Historical forecast guidance An archive of historical model forecasts combined with an associated archive of verifying observations enables useful post-processing of current forecasts. Current forecast guidance Model forecasts are used by human forecasters as guidance for official NWS forecasts.
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SOURCE�� SEC Web site, http����www.sec.noaa.gov�index.html. SOURCE�� SEC Web site, http����www.sec.noaa.gov�index.html.
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, has run operationally since 2001 (Du et mation about the uncertainty associated with the forecast.
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for (a) the ensemble of initial conditions and (b)
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3-3 fixed image This product is experimental and uncalibrated, but provides impact of possible new observations on model performance information about the uncertainty associated with each and allows data assimilation developers to test new ideas in parameter from the spread of lines within each panel. Both a controlled setting.
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Finding: A number of methods for generating initial ensembles are being explored in the research and operational 3.1.2 Accounting for Model Error in Ensemble Forecasting communities. In addition, ensemble-based data assimilation approaches are proving beneficial, especially at the A limitation of any ensemble construction methodology mesoscale.
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46 COMPLETING THE FORECAST BOX 3.4 Ensemble Forecasting and Ensemble Initial Conditions Background The aim of ensemble forecasting is to provide uncertainty information about the future state of the atmosphere. Rather than running models once from a single initial condition, a collection of initial conditions are specified and the model is run forward a number of times.
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47 ESTIMATING AND VALIDATING UNCERTAINTY BOX 3.5 THORPEX -- A World Weather Research Programa THORPEX is a part of the World Meteorological Organization (WMO) World Weather Research Programme (WWRP)
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Historical model information is available in four forms: archived analyses, reanalyses, archived forecasts, and reforecasts. The archived analyses and forecasts reflect the 3.1.3 Model Development state of the forecast system at the time of their generation; The MMB SREF approach uses an ensemble system with data assimilation methodologies, observations, and models 32-km grid spacing and the output available on 0-km grids.
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statistics are available for maximum temperature, minimum NWS does little post-processing of its ensemble forecasts temperature, and PoP as a function of geographical region, forecast lead time, and numerical model.1 to provide reliable (calibrated) and sharp probability distributions (see also Chapter , recommendation )
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FIGURE 3. Example of probabilistic forecast of precipitation amount based on MOS applied to the Global Forecasting System model output.
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Ultimately, the NDGD would include objectives of emergency management and their temporal information from both the global and the mesoscale model- and spatial determinants and providing emergency managers ing systems. with information on what is feasible in terms of forecast uncertainty descriptors from operational forecast systems.
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In addition, for a paradigm shift from deterministic variety of statistical and analog models with the output of to probabilistic forecasting to be useful for a variety of users, the recently implemented Climate Forecast System (CFS) a means of participation of such users and intermediaries numerical weather prediction model, which was developed in the forecast product design and communication phases and is run operationally by the NCEP Global Climate and is critical.
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Information about prediction skill should be addition, the center should make use of reforecast data more readily available to users. sets and historical forecast performance information for developing the monthly and seasonal probabilities.
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role as both a user and a provider of NWS forecasts. Finding: The CTB provides an opportunity for the CPC to 3.3.1.1 Operational Hydrology Products efficiently incorporate new knowledge and technologies into their forecasting processes.
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Lack of representation of the skewed supply volume regressions on several variables including streamflows by this approach generates significant questions of reliability for the generated exceedance quantiles.2 snow pack information and seasonal forecasts of temperature and precipitation. The regressions provide a deterministic water supply volume (representing the 0 percent exceed- 2SeeNatural Resources Conservation Service seasonal flow methods, ance forecast)
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56 COMPLETING THE FORECAST FIGURE 3. Example deterministic stream stage forecast from the CNRFC map of Figure 3.. SOURCE: California Department of Water Resources/NWS California Nevada River Forecast Center.
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57 ESTIMATING AND VALIDATING UNCERTAINTY BOX 3.8 Operational Hydrology Observations Onsite Data Onsite data are obtained from precipitation gauges of various kinds (weighing or tipping bucket, heated or not heated, shielded or not shielded) , surface meteorological stations, soil moisture data, and stream stage or discharge stations.
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the input time series or fields of surface model input and which are generated by objective or in some precipitation, temperature, and potential evapotranspira- cases subjective procedures applied to the operational NCEP tion; (b) the operational hydrologic model structure and model forecasts.
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The challenge Prerequisites to successfully addressing the aforemenin this case is to develop objective procedures to use NCEP tioned challenges are the development of (1) adequate short-term and seasonal surface precipitation and tempera- historical-forecast databases at NCEP to allow bias removal ture forecasts in conjunction with the ESP-type forecasts for of the NCEP forecasts, and (2)
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Another challenge is therefore to develop feedback elements. The probability distribution of the model state procedures so that hydrologic model states, such as soil is the new state of the fully probabilistic system, and any moisture and snow cover, may be used to better condition changes (including forecaster changes)
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This issue can be correctly resolved only if the the local level, each forecast office produces Area Forecast same meteorological model structure and ensemble predic Discussions several times a day that analyze the weather tion methodology is used in short-term weather forecasts and situation and provide insights into the forecaster's analysis, long-term climate predictions, and the full range of products including his or her relative certainty regarding the forecast. becomes available routinely by NCEP from both weather and At some NWS offices, short-range area forecast discussions climate model output.
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knowledge, as well as the model guidance and other observa On a national level, the HPC produces a variety of forecast tions and tools. Watches and warnings issued by the SPC also discussions that communicate uncertainty, including a Short may provide some information about the likelihood of severe Range Public Forecast Discussion, an Extended Forecast weather, through wording of the discussions, but they do not Discussion, a Quantitative Precipitation Forecast Discussion, explicitly include uncertainty information.
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Two examples of ways verification information can be made more relevant are (1) the provision a http����www.bom.gov.au�bmrc�wefor�staff�eee�verif�verif_web_page.html.
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forecast verification efforts tend to treat model gridpoints independently.3 The implication is that the NWS tion approaches generally provide much broader information about forecast performance than can be obtained from goal is to produce unbiased, reliable probabilistic forecasts a more traditional verification approach that focuses on of individual weather elements at individual locations. This single verification measures.
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Verification inforstraightforward way for NWS to provide forecast uncertainty mation should be kept up to date and be easily accessible information is to augment existing forecast products with the through the Web. error bars implied by historical verification statistics.
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