Why this March is different - plausible correlation to SSW

[Typhoon Tip]

As we know, Sudden Stratospheric Warming events, particularly those that subsequently propagate downward (downwelling..) from their emergence altitudes (5hPa (mb) levels), ultimately to penetrate the tropopausal levels are highly correlated to -AO.    The correlation is not immediate; there is an approximate 20 to 30 day time-dependency as the propagation takes place.   

 

Around the middle to end of January, a robust SSW event took place, and the subsequent downward propagation was demonstrated:

 

 

Note the "nodal" appearance of local time scale warm pockets along the general deceleration of the downward moving thermal anomaly out in time?  This is quite common/classic when observing propagating events since monitoring of the stratosphere-troposphere interactivity began 30 years ago.  This year was no different.  

 

I believe this is also in part culpable in why this particular March appears destined to be more winter like compared to Marches of recent years.  There are other factors that drive anomaly distributions - of course - but the Arctic Oscillation, as shown below, was modestly negative, but then really accelerated and became heavily suppressed since the middle to end of February and presently:

 

 

There have been other SSW's in the past that were less evidenced in the correlation on the AO into March, but this particular one appears dominating in spatial magnitude, and therefore, having greater mass integration might suggest why.

 

More specifically to our local hemispheric region ... there are 3 teleconnectors that can often signal cool departures:  Those being, the PNA, the EPO and the NAO.   Each has a different character in how the cold is signaled.  For PNA, a rising PNA during antecedent cold events over the Canadian Shield can often mean bringing that cold south when/if the +PNA attributed western heights rise, ... effectively tipping the flow NW over Canada.   There are other means to transport cold, as well.   A falling EPO may mean heights rising over the Aleutians and Alaska; if amplified enough, this can also motivate Siberian air over the pole, which floods Canada.  Even with a relatively flat PNA underneath, any subtle permutation in the flow that allows for that weighty air to press south will tend to flood the NP to GL regions ... often setting the stage for storminess where that cold kisses the jet stream/westerlies.   The NAO rising to neutral, then falling negative, then rising to neutral, then falling...etc, etc, can also supply cold anomalies to the GL/OV/MA/NE regions, particularly if that takes place during a -AO phase.  

 

In this particular case it appears the -AO protracted bias, then having a NAO doing just that, is likely to offer some lengthier finish to winter over recent years.   

 

Below on the left is the NAO as offered by the operational Euro from 12z today (and I assure you this has been in very good continuity over many cycles of the product) and the 00z GFS ensemble mean on the right.   This shows multi-guidance type agreement that the NAO is in no hurry to flag a warmer signal!

 

 

 

To re-iterate, with the antecedent AO being so heavily suppressed, this kind of pulsing negative NAO is flagging a really impressive cold signal for this time of year, for the GL/OV/at least upper MA and NE regions.  It is no wonder why the operational runs are breaking waves ... piling them up under, or near our latitude, because with all that train wreck in the N Atlantic, the impulse dynamics have no where else to go.  The operational runs with increased cold and storm signatures are both intuitively correct, but are correlated statistically well at this time.   Until these overwhelming, overriding teleconnectors break down, I am afraid that spring will only be realized by chancy encounters like this warm up early this week, or not at ...perhaps through the last week of the month!

[CoastalWx]

Nice post John. The warming has been interesting to follow!