MJO Strong Influence on North America Climate
Fig. 1: Influence of a strong MJO episode near the Dateline on the northern hemisphere upper air pattern the next 15 days.
Discussion: A moderate-to-strong convection phase of the Madden Julian oscillation (MJO) is present near the Dateline in the tropical Pacific Ocean. The heat release from this convection tilts northeastward from the tropics and into the northeast Pacific causing the subtropical high-pressure ridge in that zone to amplify.
The amplified ridge in the East Pacific is compensated for by a deep upper trough over central North America which is entraining arctic air cross-polar from Russia to generate what is likely the coldest mid-February on record for the Great Plains.
In the northern Atlantic Ocean a deep trough over the relatively cool SSTA pattern southeast of Greenland (compared with the robust warm SSTA of the northwest Atlantic basin) is persistent. This upper trough has been semi-permanent this winter season bringing frequent storms to Western Europe. The upper trough in this position is in response to a relatively new climate regime known as the North Atlantic Work Hole (NAWH) whereas a persistent cooler than normal SSTA region persists southeast of Greenland while surrounded by typically warmer than normal ocean water. The NAWH formed in 2013.
In-between the NAWH upper trough and the MJO-induced compensating trough over North America an upper-level high pressure ridge is located off the Southeast U.S. coast.
The pattern described is mostly generated by the amplified MJO in the Pacific and secondly by the persistent trough west of Europe. The “polar vortex” trough in central North America is made stronger by cross-polar arctic air from the Russia source region born earlier this winter season.
The stratosphere is cold and turns colder the next 15 days. Implied is the arctic air in the pattern now was generated earlier this winter (and not in the current pattern). Additional arctic air is not likely due to the projected cold stratospheric temperatures into early March.
The current pattern is certainly cold with widening snow cover. The snow cover will enhance the cold next week. However, based on the stratospheric forecast the ability to lose the very cold mid-February climate character by March 1st is increasing rapidly.
Fig. 2: An amplified MJO on phase_6/phase_7 (near the Dateline) is forecast to continue another week or so by ECMWF.
Fig. 3: Cross-polar arctic air is in the pattern and once that’s gone the cold stratosphere forecast implies additional arctic air generation is not likely.