In 2013 State Climatologist Nicholas Bond of the University of Washington noted an unusual warming of the northeast North Pacific which during 2014-15 strengthened and did not weaken until 2016. The large area of warm water correlated to an upper level ridge pattern associated with the downstream polar vortex winter of 2013-14 and 2014-15 and was a major contributor to California drought. A weaker version of this phenomenon formed in 2017 southwest of California (pictured) and has contributed to another drought and record 2017 fire damage.
A measure of the atmosphere’s reaction to the ENSO regime is multivariate ENSO index (MEI). During the past 2 months MEI has shifted from weak La Nina to neutral ENSO. Expected next week is that NOAA will announce La Nina onset due to the cooling east-central Pacific (Nino34 zone) sea surface temperature anomalies (SSTA). But does the climate agree?
According to the Rutgers University Snow Lab the North America snow cover in November 2017 was 7th highest in the 1966-2017 period of record. Interestingly, the November 2017 value is similar to November 2013 and 2014 which were followed by “polar vortex winters”.
Snow cover is currently well below normal for early December across the North-Central to Northeast U.S. But that regime changes beginning this week and especially next week as a polar vortex weather pattern develops and combined with the relative warm Great Lakes causes widening snowfall (and snow cover).