A CALIBRATION OF THE LAMB AIR-FLOW CLASSIFICATION MODEL TO PREDICT PAST PRECIPITATION IN WALES

Daily precipitation data from 146 sites for the period 1982 to 1991 in clusive have been analysed in conjunction with the 27 Lamb airflow typ es. An areal mean precipitation (AMP) series for Wales is constructed for the period 1861 to 1995 by summing the mean daily AMP values assoc iated with each Lamb airflow type. The results reveal that the use of coherent precipitation regions together with seasonal AMP values are m ore likely to provide a better estimate of mean annual precipitation t han those combining a simple unweighted summation with non-seasonal va lues. The mean annual series for Wales compares favourably with that p rovided by Wigley et al. and Woodley for England and Wales. Finally, t he importance of the major Lamb airflow types are considered in relati on to periods of the record when dry and wet phases occur. Anticycloni c and cyclonic Lamb types are shown to be better predictors of mean an nual precipitation than Lamb westerlies. In part, this reflects the fa ct that at the regional scale non-westerly Lamb airflow types can be e mbedded within a mobile westerly circulation. These non-westerly airfl ow types often produce high precipitation totals over Wales. (C) 1997 by the Royal Meteorological Society. (C) John Wiley & Sons, Ltd.