Dynamical Extended-Range Forecasts of the Lower Tropospheric Thickness

Abstract

National Meteorological Center dynamical extended-range forecasts of daily as well as time means of lower tropospheric thickness (700 mb height minus 1000 mb height) are analyzed in this paper. Daily forecasts show significant skill until about 11 days when they are in distinguishable from randomly selected states. Forecasts of time averages show significant skill for almost all averages, especially if the appropriate averaging period of the forecast is selected. The correlation between the forecast average over the first 10 days and the observed average over the 30-day period starting at the same time is about 0.25. No better way of forecasting the 30-day average, on average, was found for this data. Large variations in skill occur with the most skilful periods corresponding to decreased baroclinicity. Composite states of high and low skill show that over the United States 30-day means that have a warm west coast with high pressure aloft and a cold cut coast with low pressure aloft is predicted best by the model. Predictability analyses in which the model is compared with itself rather than with the observations indicate an even greater potential predictability.