Forecasting of the onset and duration of blocking remains a major problem for Australian forecasters. The consequences of blocking may manifest themselves as drought, as for example experienced during the winter of 1982 over much of Australia. On other occasions cut-off flow associated with blocking episodes can cause extensive heavy rain. Subjective methods of predicting blocking have met with only limited success and numerical models now form the basis for broadscale prediction. A number of experimental simulations of blocking will be briefly described. Generally the simulations have reproduced, but not adequately explained, the phenomenon. Reference is then made to operational numerical prognoses undertaken at the National Meteorological Analysis Centre (NMAC) during June. Two ECMWF ten-day forecasts run from analyses at the start of the blocking periods are presented as examples of the level of skill achievable in the southern hemisphere with an advanced high resolution model. Although the general three wave pattern was correctly forecast, details such as the latitude of the eastern Australian blocking high were not well handled. These are very much associated with smaller scale synoptic systems which provide the catalyst for the 'displacement/replacement' process.
P. F. Noar (Tue,) studied this question.