The Importance of High Latitude Blocking in The Upcoming Winter
In our winter forecast, we discussed certain signals that supported high-latitude blocking developing for the middle and late periods of this upcoming winter. High-latitude blocking often comes with negative phases of the North Atlantic Oscillation (NAO), the Artic Oscillation (AO), and/or the Eastern Pacific Oscillation (EPO). High-latitude blocking is one most important factors in any winter forecast, as it typically supports colder temperatures and larger snowstorms for the Northeast US. This is an even more important factor in during a strong El Nino winter, as the Pacific or Subtropical jet is generally more active and stronger.
Research from Al Marinaro (@wxmidwest ) brought to light a strong correlation between the sea-level pressures in North Pacific and the NAO modality, during +ENSO (El Nino) winters. North Pacific sea-level pressures less than 1013 mb had a -NAO value on average for the December, January, February, and March period (DJFM). Sea-level pressures above 1013 mb during the month of October had either a positive NAO value or very close to netrual in the following winter. An official pressure for North Pacific reading has not been released for October yet. However, NCEP/NCAR reanalysis tells us that sea-level pressures were on average around 1010 mb over the region 65N-30 & 160E-140W in the North Pacific. That would be well-below the 1013mb threshold for a -NAO DJFM.