MJO To Influence U.S./Global Climate in late April/early May
Fig. 1: The Madden Julian oscillation 30-day forecast by the ECM indicates in
Discussion: During northern hemisphere spring La Nina events have a tendency to weaken. The weakening is caused by eastward transition of the Madden Julian oscillation, an area of heavy tropical convection from very warm waters in the West Pacific tropics eastward and erasing the La Nina-biased cool waters of the tropical East Pacific. A MAJOR effort on the part of the MJO takes place the next 2 weeks (Fig. 1).
The historical influence of MJO shifting across the tropical East Pacific (phase_8) to the tropical Atlantic (phase_1) identified by NOAA/CPC is reviewed (Fig. 2-3). In the U.S. phase_8 typically brings a warm-up to the Midwest States where recently an unusual late season freeze occurred. Expect milder conditions ahead. However, phase_1 of the MJO indicates a cool pattern returns to the U.S. Expect that trend in the 11-15-day forecasts. On the precipitation side, the MJO P8/P1 regimes favor wet weather in the South and Continental Divide regions. Operational forecast models are likely too wet North and East right now.
Fig. 2-3: NOAA/CPC historical temperature and precipitation relationships of MJO (phase_8 and phase_1) for the U.S. as we head toward May.
The greatest influence of MJO is in the tropical/subtropical climate regime. MJO phase_8/phase_1 historically represents a drying influence on the Australian climate and wetter influence on the South America climate (Fig. 4). Southeast Asia influence is also generally dry.
When MJO is forecast to have intensity as indicated now, the historical relationships of MJO on climate have a tendency to out-forecast operational models in the medium-range time scales.
Fig. 4: The NOAA/CPC historical effect on vertical motion in the tropics. Red = subsidence which has a drying effect on climate. Blue = convection which has a wet influence on tropical climate.