During the past 10 years, a semi-permanent upper trough has set-up near or southeast of Greenland frequently compensated for by a downstream upper ridge over Europe. When that Europe ridge is present, the record warm Mediterranean Sea is helping to intensify the upper ridge pattern helping to explain the recent unusual early January warmth.

The pre-Christmas 2022 arctic outbreak in the U.S. was caused by a sudden combination of stratospheric factors over the polar region and North America just-after mid-December. This type of arctic air catalyst can occur quickly and is difficult to forecast in the medium-range and certainly 3-6 weeks out. Suddenly, arctic air evolves fast in Northwest/West Russia the next 7-10 days expanding across Eurasia (although moderating) in the 11-15-day period. This type of an event can easily regenerate over North America the second half of winter.

The 2020-22 La Nina has produced wide variation in ENSO diagnostics. Multi-variate ENSO index has consistently indicated a La Nina climate while Nino34 SSTA, the conventional ENSO phase diagnostic, has been choppy and subsurface upper ocean heat has varied widely during the 3-year period.