How Might La Nina Influence the 2017-2018 Winter (credit: NWS NOAA Climate Prediction Center)

DISCUSSION: As we get further into the 2017-2018 Winter season, there is no question that there are a lot of important questions which still remain.  One big question is as to whether or not there will be prolonged periods of particularly colder weather across the northern tier of the United States.  This is a critical question which bears much concern due to the fact that more frequent Arctic air outbreaks can often times lead to there being a greater propensity for more memorable winter storms.  That is chiefly due to the fact that when colder air is more prevalent throughout a given winter, there is consequently a greater prevalence of geographic regions characterized by stronger baroclinicity (i.e., a more rapid change in temperature over some given horizontal distance).  Thus, with stronger baroclinicity in place, this facilitates a more favorable atmospheric environment for any low-pressure systems which develop with these "baroclinic zones."  Attached above is a typical storm track and temperature/moisture trend map for both the warm and cold phase of ENSO courtesy of the NOAA NWS Climate Prediction Center.

Moreover, when such low-pressure systems are suppressed further south (e.g., often in the vicinity of the Gulf Coast region), this allows those low-pressure systems to pick up plenty of warm, moist "tropical" air which frequently sets the stage for a classic coastal winter storm or more often referred to as a "Nor'easter."  Thus, monitoring larger-scale climate patterns such as the Arctic Oscillation which is effectively a proxy by which the semi-permanent statistically-identified "Arctic low-pressure system" is measured with respect to its average strength (i.e., based upon its shorter- and longer-term minimum central pressure).  When this semi-permanent "Arctic low" is weaker in strength, this more often than not allows for colder air to make its way towards the mid-latitude regions of the world.  A perfect example of this situation is precisely what is happening at the present time across the North-Central and the Northeastern regions of the United States where a lobe of the core of the Arctic air from the southern edge of the Arctic Circle has descended down into the northern tier of the United States.  Depending upon how long this and other cold air outbreaks persist along with how active the more southern storm-track remains, this will largely dictate how active the Winter season is.

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©2017 Meteorologist Jordan Rabinowitz