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).
La Nina is looking stronger and may last longer than previously forecast. Additionally, the idea that El Nino could regenerate later in 2018 is now less likely. A La Nina global climate is now more certain through the first quarter of 2018.