Madden-Julian Oscillation status and outlook for southern Arizona & the Sky Islands • Updated daily
The MJO is currently in a transitional phase with no strong influence on Arizona monsoon activity in either direction. Pay attention to shorter-range forecasts and local conditions rather than the MJO for guidance over the next week. The MJO signal is currently advancing through phases, suggesting this pattern may continue to evolve over the coming week.
The Wheeler-Hendon diagram tracks a weather pattern called the Madden-Julian Oscillation (MJO) — a pulse of enhanced cloudiness and rainfall that slowly circles the globe through the tropics every 30 to 90 days. The diagram is divided into eight phases based on where that pulse is located geographically. The red dot shows today's position. The trail behind it shows the past 40 days of movement.
Distance from the center matters: the further the dot is from the center, the stronger the MJO signal and the more likely it is to influence weather here. Dots inside the dashed circle indicate a weak or disorganized MJO with little predictive value. The MJO typically moves counterclockwise through the phases over several weeks.
For southern Arizona and the Sky Islands, phases 1 and 2 tend to favor monsoon rainfall during summer, while phases 6 and 7 tend to favor Pacific winter storms. The MJO is one piece of the puzzle — it shifts the odds but doesn't guarantee any particular outcome.