Around February 17-18, temperatures are forecast to plummet to -40F to -50F in Siberia to Mongolia as rapid onset of an arctic air mass develops in response to stratospheric warming stretching from Siberia to the polar region and northwestern North America. Stratospheric warming enhances an evolving negative arctic oscillation (-AO) beginning later this week followed by emergence of a moderate to strong negative East Pacific oscillation (-EPO).

A potential third stratospheric warming event forecast for the middle third of February over Siberia to northwestern North America could spawn another arctic air mass. If the attendant negative arctic oscillation (-AO) is accompanied by negative East Pacific oscillation (-EPO) a North America polar vortex pattern could emerge especially if AO and EPO are in the -1.5 range as indicated for mid-month.

Marine heat waves (MHW) southwest and east of Australia are strengthening during the summer season so far and affecting the prevailing upper air pattern governing the attendant Australian climate. The precipitation climate across Australia so far this summer season is much different from a typical El Nino climate!

What is an atmospheric river? A large and narrow stream of high intensity moisture extending from tropical influences pushed by the jet stream across mid-latitude land masses. The North Pacific atmospheric river is the most famous (and effective). What causes an atmospheric river to form? The best way to create an atmospheric river is the phasing (or connection) between the storm track propelled by the subtropical jet stream and increased heavy convection in the deep tropics enhanced by presence of large areas of strong vertical currents known as the positive (or convection) phase of the Madden Julian oscillation (MJO).