We have developed an approach for presenting probabilistic forecasts of the Madden-Julian Oscillation (MJO) based on the community standard Real-time Multivariate MJO (RMM) index, trialled here using forecasts from POAMA-2 (left panel above). This new method compliments the traditional MJO ensemble forecast display and overcomes the difficulty of interpreting a dispersive ensemble plume (right panel above).
We directly quantify the probability for the MJO to occur in each of its eight RMM-defined phases, as well as the weak phase, by producing one plot for each pentad out to 40 days lead time. Probabilities for the MJO occurring in each phase are displayed using a graded color scale at intervals of 20% ranging from 10% (light green) to 90% (dark blue), with probabilities lower than 10% shaded in grey and probabilities higher than 90% shaded in purple. The outer limit of the color "wedge" in MJO phases 1-8 reflects the forecast mean RMM index amplitude (calculated over the corresponding ensemble members), and the range of ensemble member amplitudes about the mean is shown with grey bars. The centered 5 day running average of the ensemble mean, calculated each day of the forecast, is also shown (black curve), noting that 5 day running averages for days 1 and 2 of the forecast include ALI reanalysis data prior to day 1.
For further information contact Andrew Marshall, or refer to "Visualizing and verifying probabilistic forecasts of the Madden-Julian Oscillation" by A. G. Marshall, H. H. Hendon and D. Hudson (2016).