What is the Madden Julian oscillation? There are 2 phases of the MJO, the subsidence and convection phase. The convection phase is born in the equatorial Indian Ocean caused by the differential heating between the warm oceans and rising/cooling Asian land mass to the north. The MJO convection phase shifts east slowly navigating the global tropics typically in 6-7 weeks with varying intensity. The MJO tends to be strongest over equatorial waters that are warmer than normal as they are throughout the equatorial West Pacific right now. The MJO convection phase causes drenching tropical rains, increases tropical cyclone risk and if sufficiently intense can alter mid-latitude jet streams enhancing storm tracks which can produce weather extremes including violent storms and excessive warmth and cold. Get ready, we’re about to witness such an event.
Discussion: The GFS is strongest with an emerging convection phase of the MJO in the far West Pacific equatorial region next week (Fig. 1). The event is stronger than a recent buoyant episode occurring last October in this region. The convection phase of the MJO is more intense than usual due to the warmer than normal surface waters north and northeast of Australia.
Fig. 1: The GFS ensemble explodes MJO-oriented convection next week and out to 14 days in the far equatorial West Pacific.
The 15-day rainfall totals north and northeast of Australia and including coastal Northwest Australia exceed 12 inches according to the GFS ensemble (Fig. 2). Rainfall totals by these model projections are at times too high but in this case, given the projected strength of the MJO episode the amounts are realistic. Indonesia will be soaked by this rainfall.
Fig. 2: The 15-day rainfall forecast using the GFS ensemble projects excessive rainfall north and northeast of Australia. Some of the heavy rains affect Northwest Australia.
The MJO episode will have a dramatic impact on North American climate for the first third of February. The MJO episode described is stronger than a similar event which occurred December 21-25. That event was sufficiently potent to vault heat pole ward via a Rossby Wave and into the stratosphere causing a stratospheric warming event near the North Pole Christmas week. The stratospheric warming event caused arctic air to form in Canada which eventually released into the U.S. causing a 1-in-50 to 1-in-75 year cold episode to start the New Year. What’s about to happen is the same thing, but different.
Fig. 3: The ECMWF ensemble forecasts a stratospheric warming event over Northwest North America caused by the far West Pacific MJO event.
The stratospheric warming is there. The ECM ensemble forecasts warming at 10 MB late next week across Alaska/Northwest Territories (Fig. 3). The warming stratosphere causes the troposphere beneath to contract and cool forcing arctic air formation upslope the Canadian Rockies (Fig. 4). The MJO episode is a little farther west in the tropical West Pacific (versus the December event) therefore the stratospheric warming is over northwest North America and not the North Pole as observed last Christmas week. Implied is a farther west arctic air development which targets the U.S. Rocky Mountains rather than farther east as observed early this month.
Fig. 4: Stratospheric warming in early February causes arctic air to form in western Canada extending to the Upper Midwest February 2nd.
The MJO event is far enough to the west in the equatorial West Pacific to cause the cold effect on North America to be biased farther west while the Gulf of Mexico becomes tropically active with a plume of attendant heavy precipitation extending northeastward through the East U.S. the next 2 weeks. The back edge of this streak of precipitation will become heavy snow (Fig. 5) while on the East Coast it’s all rain and the ground stays bare.
The arctic cold reaches the new snow over the Ohio Valley to northern New England but east of the Appalachian Spine bare ground in the Mid-Atlantic region biases the air mass warmer therefore no arctic punch for this region this time around.
Fig. 5: The ECMWF ensemble 15-day snowfall forecast indicates piling snows Ohio to Maine but the Mid-Atlantic misses the snow necessary to attract arctic chill.