Center's Primitive Equation Research Articles

Automated Prediction of Surface Wind from Numerical Model Output

The Model Output Statistics (MOS) technique has been applied to the prediction of surface winds. Warm and cool season forecasting equations were developed by screening as potential predictors several forecast fields from the National Meteorological Center's Primitive Equation (PE) model. Four additional weather parameters from surface reports were also screened to provide the latest observed conditions for the initial forecast projection. Separate equations for the U and V wind components and wind speed, S, were derived for each of 233 stations for projections of 12 to 48 b. For any given station and projection, the U,V, and S equations were required to use the same predictors. Initially, the first three predictors were forced to be boundary layer U,V, and S forecasts from the PE model. Comparative verification was carried out on independent data for test forecasts at 20 widely distributed stations during warm and cool seasons. In addition, operational guidance forecasts were verified for 92 stations during November 1973 to March 1974. Both of these tests suggested that although the automated method tended to underforecast strong winds, its objective forecasts were generally more accurate than the subjective National Weather Service forecasts. Adjustment and transformation procedures to enable the automated system to produce more strong wind forecasts were also tested.

An Operational Experiment in the Statistical-Dynamical Prediction of Tropical Cyclone Motion

Abstract Current statistical models for the prediction of tropical cyclone motion use predictors derived from climatology, persistence, and observed geopotential height data. This paper describes an operational experiment conducted during the 1973 and 1974 Atlantic hurricane seasons whereby prognostic 500 mb height data from the National Meteorological Center's primitive equation model were also included as statistical predictors. Both the “perfect-prog” and a “simulated-model-output-statistics” (SMOS) approach were utilized to introduce the prognostic height data into the statistical prediction equations. Compared to the current “state-of-the-art” of tropical cyclone forecasting, the perfect-prog technique gave relatively poor displacement forecasts for the first half of the 72 h forecast period but excellent forecasts for the latter half. The SMOS method performed well over the entire period but the 72.h displacement error was somewhat greater than that of the perfect-prog equations. The results of the ...

Objective Estimation of the Conditional Probability of Frozen Precipitation

A system is developed which produces objective forecasts of conditional probability of frozen precipitation for the conterminous United States. Development of the system consists of two basic steps, in each of which the MOS (Model Output Statistics) concept is used. First, for each of 186 stations, we find a “50%” value for each of three variables predicted by the National Meteorological Center's Primitive Equation (PE) model: 1000–500 mb thickness, boundary-layer potential temperature, and 850-mb temperature. For instance, we find the value of the 1000–500 mb thickness which indicates a 50–50 chance of frozen precipitation at a particular station, provided precipitation occurs. These 50% values are determined by using the logit model to fit data from three winter seasons, September 1969 through March 1972. Secondly, the deviations from the 50% values are determined for each station for each variable; the relative frequency (for those cases when precipitation occurred) of frozen precipitation is then computed, again with the logit model, as a function of these new variables. In order to get stable results in this last step, data for all stations are combined. In addition to the meteorological variables, we also use the first harmonic of the day of year and station elevation as predictors. Separate logit equations are determined for each of the PE run times, 0000 and 1200 GMT, and for each of four projections, 12, 24, 36, and 48 hours. This system was put into operation by the National Weather Service in November 1972. Both teletypewriter and facsimile products are being distributed to field offices twice daily. A comparative verification on independent data for the 12- and 36-hr forecast projections shows the objective system produced better forecasts than those prepared subjectively at the National Meteorological Center.

Use of Model Output Statistics for Predicting Ceiling Height

Abstract The model output statistics (MOS) technique consists of determining a statistical relationship between the forecast output of numerical prediction models and a predictand. This paper presents some results obtained in applying the MOS technique to the prediction of ceiling height by means of screening regression. Data from 3 winter seasons and 95 eastern U.S. stations are combined in a generalized operator approach to develop multiple regression equations. The potential predictors subjected to screening include surface variables observed at 0700 GMT and forecast output from both the National Meteorological Center's primitive-equation model and the Techniques Development Laboratory's subsynoptic advection model. Prediction equations are developed for 5-, 11-, and 17-hr forecast projections representing ceiling height forecasts valid at 1200, 1800, and 2400 GMT, respectively. Ceiling height is treated both as a categorized and as a continuous predictand. Where ceiling height is categorized, the regr...

Further Experiments in Localized Numerical Weather Prediction

Abstract Local numerical forecasts generated by interpolation from the National Meteorological Center primitive equation model are evaluated for the 1969–70 winter season in the eastern United States. A marked under-prediction of precipitation frequency appears to he due, at least in part, to the interpolation system.