As seen from this SST anomaly chart
http://weather.unisys.com/surface/sst_anom.html I think it's not really a classic El Nino. There are 2C positive anomalies over the northeast Pacific and the central Atlantic. I think both features are tending to lock ridging in those locations with troughing into the midwest and north-central US. As the flow around the Pacific ridge slides down the Rockies spine from Alaska it would seem to undergo radiational cooling that encourages little short-waves and cut-offs into the southwest US that find their way eastward into the main flow.
If the pattern is locking in for awhile as the GFS may be suggesting, the prog is coooooold and dry in the north-central and upper midwest regularly blasting to the east coast, unsettled in the southwest and Texas, and downright ugly in the southeast up through the mid-Atlantic. Happy New Year, you poor suckers!
