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- Author or Editor: George J. Maglaras x
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Abstract
A Model Output Statistics system for forecasting the conditional probability of precipitation type (PoPT) became operational within the National Weather Service in September 1978. Forecasts are provided for three precipitation type categories: snow or ice pellets, freezing rain, and rain. To develop the forecast equations, data are combined from different stations because of the limited amount of developmental data. To justify combining the data, the Limited-area Fine Mesh (LFM) model predictors are transformed from their original values through the use of the logit model. In one experiment, it is shown that probability of snow forecasts are made more accurate through an improved use of the logit model for predictor transformation.
The new transformation procedure is then used in the development of a set of experimental PoPT forecast equations. The experimental equations differ from the operational equations in other ways also. The developmental sample for the experimental equations included approximately three winter seasons more data than the sample used for the operational system. Also, improvements are made to the potential predictors used to develop the experimental equations. Finally, freezing rain mixed with any other precipitation type is defined as freezing rain in the experimental system; in the operational system, this mixture of precipitation is defined as rain.
A comparative verification between the experimental and operational systems on independent data indicates that, overall, the experimental PoPT forecasts are better than the operational forecasts, especially for 12–24 h freezing rain forecasts. Based on these results, new operational PoPT forecast equations are developed incorporating the features associated with the experimental equations. The new system was implemented in the fall of 1982.
Abstract
A Model Output Statistics system for forecasting the conditional probability of precipitation type (PoPT) became operational within the National Weather Service in September 1978. Forecasts are provided for three precipitation type categories: snow or ice pellets, freezing rain, and rain. To develop the forecast equations, data are combined from different stations because of the limited amount of developmental data. To justify combining the data, the Limited-area Fine Mesh (LFM) model predictors are transformed from their original values through the use of the logit model. In one experiment, it is shown that probability of snow forecasts are made more accurate through an improved use of the logit model for predictor transformation.
The new transformation procedure is then used in the development of a set of experimental PoPT forecast equations. The experimental equations differ from the operational equations in other ways also. The developmental sample for the experimental equations included approximately three winter seasons more data than the sample used for the operational system. Also, improvements are made to the potential predictors used to develop the experimental equations. Finally, freezing rain mixed with any other precipitation type is defined as freezing rain in the experimental system; in the operational system, this mixture of precipitation is defined as rain.
A comparative verification between the experimental and operational systems on independent data indicates that, overall, the experimental PoPT forecasts are better than the operational forecasts, especially for 12–24 h freezing rain forecasts. Based on these results, new operational PoPT forecast equations are developed incorporating the features associated with the experimental equations. The new system was implemented in the fall of 1982.
Abstract
The complex combination of synoptic- and mesoscale interactions topographic influences, and large population densities poses a multitude of challenging problems to winter weather forecasters throughout the eastern United States. Over the years, much has been learned about the structure, evolution, and attendant precipitation within winter storms. As a result, numerous operational procedures, forecast applications, and objective techniques have been developed at National Weather Service offices to assess the potential for hazardous winter weather.
An overview of the challenge of forecasting winter weather in the eastern United States is presented, including a historical review of several legendary winter storms, from the Blizzard of 1888 to the Halloween Nor'easter of 1991. The synoptic-scale features associated with East Coast winter storms are described. The mesoscale nature of many eastern winter weather events is illustrated through an examination of the Veterans' Day Snowstorm of 11 November 1987, and the Long Island Snowstorm of 13 December 1988. The development of applied forecast techniques and the potential for new remote sensing technologies (e.g., Doppler weather radar and wind profilers) and mesoscale models to improve operational forecasts of winter weather hazards are also discussed. Companion papers focus on cyclogenesis, terrain-related winter weather forecast considerations in the Southeast, and lake effect snow forecasting.
Abstract
The complex combination of synoptic- and mesoscale interactions topographic influences, and large population densities poses a multitude of challenging problems to winter weather forecasters throughout the eastern United States. Over the years, much has been learned about the structure, evolution, and attendant precipitation within winter storms. As a result, numerous operational procedures, forecast applications, and objective techniques have been developed at National Weather Service offices to assess the potential for hazardous winter weather.
An overview of the challenge of forecasting winter weather in the eastern United States is presented, including a historical review of several legendary winter storms, from the Blizzard of 1888 to the Halloween Nor'easter of 1991. The synoptic-scale features associated with East Coast winter storms are described. The mesoscale nature of many eastern winter weather events is illustrated through an examination of the Veterans' Day Snowstorm of 11 November 1987, and the Long Island Snowstorm of 13 December 1988. The development of applied forecast techniques and the potential for new remote sensing technologies (e.g., Doppler weather radar and wind profilers) and mesoscale models to improve operational forecasts of winter weather hazards are also discussed. Companion papers focus on cyclogenesis, terrain-related winter weather forecast considerations in the Southeast, and lake effect snow forecasting.
