Over the last few weeks, we’ve been in a pattern that has feature more extreme arctic intrusion that with the low temperatures that we have for NYC in many years.  Record lows where shattered on Friday morning over the Tri-State area. What is amazing is that we seen the Artic Oscillation and North Atlantic Oscillation remain positive. The arctic air is from a combination -EPO and +PNA. The question is how long does this pattern continue. Well the models and ensembles show -EPO/+PNA gradually retrograding into Central Pacific, over next two weeks. Some support for this pattern change is the MJO looking become neutral to unfavorable the next few weeks. As tropical forcing at 200mb and 850mb diminishes in Western Hemisphere and reemerges over the Indian Ocean and Indonesia, during the 2-3 weeks.

However, the Pacfic SSTs continue to show a strong +PDO and weak, west-based +ENSO. If there’s no change here, this could support a reload of -EPO/+PNA again sometime in March, provided we see the forcing mechanism for it again.

The ECMWF shows more perturbations with the stratospheric vortex over next 10 days. However, these perturbations appear to be related to changes in troposphere or 200mb-500mb level. There is no significant warming or decrease in westerly winds occurring at 10mb and 60N. Despite more significant warming episodes previously, the stratospheric vortex has remained intact for most part this winter, particularly at 50mb. So I think the AO and NAO will continue remain largely on the positive side going into March  Some weak or transient -AO/-NAO episodes are possible from time to time with each polar vortex perturbation.

For sensible weather in the Tri-state area, I expect very cold air intrusions to continue this week. Then a gradual moderating trend with temperatures during the first ten days of March. Temperatures will still likely average below normal. But should come out of the deep freeze that we’ve seen the past couple weeks.  The southern stream remains active enough, to keep potential going for more wintry threats in this pattern.  However, with the lack of high-latitude blocking and a sustained West Coast ridge,  don’t expect anything major or historic for the Tri-State area. Chances are flow will wind being too fast over the area, for any cold high pressure to remain to our north or the trough to take extreme negative tilt and close off at 500mb. Parts of Northern and Central New England, which has seen historic snowfall this year, may a different story. But even there the pattern may be to progressive. When any threat on the models appears to be legit, I will discuss more in the wintry wx section.