Just when you thought it was safe to predict a milder than average winter in Minnesota.
NOAA’s winter outlook came out this week. As expected, it favors a milder than average winter across the northern and western U.S. including Minnesota.
Here’s more detail on the thinking behind NOAA’s winter outlook.
Previous trends in the tropical Pacific favored a weak El Niño event this winter. Weak El Niño events (+0.5C) exert less predictable influence on wintertime upper air patterns in the northern hemisphere than moderate (+1.0C) or strong (+1.5C) El Nino events.
Here’s the typical average wintertime upper air pattern over North America in a moderate or strong El Niño event.
The latest trends now favor a more moderate El Niño event.
The latest October ensemble average from the suite of ENSO models calls for a slightly stronger #ElNino event than was predicted in September. New ensemble average calls for borderline weak/moderate event peaking around 1°C in December-February. pic.twitter.com/hWLHYMXOUf
— Philip Klotzbach (@philklotzbach) October 19, 2018
“Modoki” El Niño event?
This winter’s El Niño event may be showing signs of evolving into a so-called “El Niño Modoki” event.
Most El Niño events feature warmer than average ocean water in the eastern Pacific off the coast of South America. But El Niño Modoki events feature warm water in the central Pacific, bracketed by colder water to the east and west.
Here’s more from the Japan Agency for Marine-Earth Science and Technology. (JAMSTEC)
El Niño Modoki is a coupled ocean-atmosphere phenomenon in the tropical Pacific. It is different from another coupled phenomenon in the tropical Pacific namely, El Niño. Conventional El Niño is characterized by strong anomalous warming in the eastern equatorial Pacific (see figure above). Whereas, El Niño Modoki is associated with strong anomalous warming in the central tropical Pacific and cooling in the eastern and western tropical Pacific (see figure above). Associated with this distinct warming and cooling patterns the teleconnections are very different from teleconnection patterns of the conventional El Niño. Hence, the new phenomenon is of interest to the climate community.
Jet stream pattern during an El Niño Modoki winters may vary from typical El Niño winters. That can impact temperature trends across North America.
Probably milder, but…
There are two strong reasons to predict a milder than average winter this year. The likelihood (70% to 75%) of an El Niño event this winter is one. The longer-term trend of a strong winter warming signal in Minnesota is another. So the climatological forcing mechanisms favor a milder than average winter this year.
But confidence is lower than in most El Niño winters. The El Niño Modoki may throw jet stream patterns into disarray. That leaves open the possibility of more frequent polar outbreaks.