Earlier in today's forecasts we mentioned stratospheric warming over northern Canada causing some extreme cold into the northern U.S. Christmas week. Now let’s evaluate the role of the MJO. The MJO forecasts vary but Climate Impact sides with the persistence forecast (GFS) for days 4-8/6-10 followed by a progressive MJO toward the Atlantic (as indicated by the ECMWF). The implications are an eastward shift of the anomalous warmth anchored West (recently toward the East Coast while the cold pattern in the East retreats to snow cover. In the 11-15 day period the MJO shift s to the Atlantic and coupled with stratospheric warming leads to an arctic outbreak into the Central U.S. Briefly very warm East ahead of that cold air.

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”.