Numerical Weather Prediction Products Research Articles

Medium- and Long-Range Forecasting

Abstract In contrast to short and extended range forecasts, predictions for periods beyond 5 days use time-averaged, midtropospheric height fields as their primary guidance. As time ranges are increased to 3O- and 90-day outlooks, guidance increasingly relies on statistical techniques using autocorrelation fields rather than numerical weather prediction (NWP) products as the primary prediction tool. The basis for the medium-range 6- to 10-day forecast is a mean 500 mb height and anomaly field for the forecast period, derived from a mix of output from two different numerical models, with some statistical and subjective modification added if desired. The monthly or 30-day outlook is based on a subjectively constructed mean 700 mb prognostic map based on available NWP mean height and anomaly fields out to 10 days, the appropriate 700 mb 1-month lag auto-correlation field, and subjective use of teleconnection and empirical orthogonal function patterns for consistency. A quantitative midtropospheric height and...