This sounds plausible:

SSWs can result in the displacement, splitting, and weakening of the Arctic polar vortex (see http://journals.ametsoc.org/doi/abs/10.1175/2008JCLI2365.1), and "pronounced weakenings of the NH wintertime stratospheric polar vortex tend to be followed by episodes of anomalously low surface air temperatures and increased frequency of occurrence of extreme cold events throughout densely populated regions such as eastern North America, northern Europe, and eastern Asia that persist for 2 months" (ref http://journals.ametsoc.org/doi/abs/10.1175/1520-0442(2002)015%3C1421%3ASCTNHW%3E2.0.CO%3B2)

I know there are a few scientists who think this is plausible, but I also know quite a few who think this is not the way it works. I think the debate is still open, but as a point of debate I would like you to think about the following. I can imagine that there us a third process that causes both the SSW (fast response) and then later also anomalous tropospheric circulation patterns. To my knowledge no one has realky shown how a SSW would be able to affect the troposphere. So, the possibility remains that the SSW is an effect, not a cause. But I could be wrong. Nevertheless, more research is needed, that is for sure.

Several papers dealing with winter annular mode anomalies (which are affected by SSWs) and the following months. I found this paper very interesting: A possible cause of the AO polarity reversal from winter to summer in 2010 and its relation to hemispheric extreme summer weather, by Yuriko Otomi, Yoshihiro Tachibana, Tetsu Nakamura.

http://link.springer.com/article/10.1007%2Fs00382-012-1386-0

Major SSW events can modified synoptic regimes in the troposphere for a long period, ... yes mechanisms should be explained more clearly, but evidences of such interaction is remarkably highlighted!

Here the observed NAM since this winter. A major SSW is evident around 10 January 2013.

http://www.lamma.rete.toscana.it/models/winter/gfs_nam_web_1.png

Nam map

Low troposphere AO values during March seems to be downstream effect of the previously stratosphere anomaly, or, at least, strongly influenced.

The MetOffice presented a report (http://www.metoffice.gov.uk/media/pdf/i/2/March2013.pdf) in April discussing different possible mechanisms for the unusually cold spring this year. Among these potential drivers is the stratospheric warming event in winter. Others include weather in the tropics, conditions ni the North Atlantic and the state of the Arctic. They conclude that no single explanation can account for the cold conditions observed in the UK in March.

I confirm that sources and causes are a subject of debate. However we know that a large part of the stratospheric variability is coming from the troposphere. It has already been shown that SSWs are due to the amplitude increase of planetary waves induced in the troposphere (see Salby et al., J. Geophys. Res., 107(D18), 4342, doi:10.1029/2001JD000421, 2002). With our data obtained in South of France, we have shown that statistically a cooling is associated with major stratospheric warmings mainly for a splited vortex.

Article Contribution of stratospheric warmings to temperature trends...

Here is also a plot showing composite time evolution during SSWs

Some interesting consideration about SSWs and Negative Arctic Oscillation Transitions :

Stratospheric Circulation Associated with Negative Arctic Oscillation Transitions - AMS Annual Meeting - 2012, New Orleans.

Abstract with Recorded presentation.

https://ams.confex.com/ams/92Annual/webprogram/Paper202534.html

A simple update of vertical cross section of geopot, reversed AO regime seems emerging, even not so intense!

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/hgt.ao.cdas.gif

It is hard to sentence that an isolated geopotential anomaly was connected to a specific Sudden Stratospherich Warming.

What we can say is that SSW can "disturb" the tropospheric circulation, causing severe weather conditions (like heavy snow, floods and blizzards) over almost all USA, Europe and Asia. The reason is due to the fact (in simple terms) that the polar vortex is weakened after the occurrence of an SSW, so latitudinal air-mass exchanges (and cyclogenesis) are more intensive at the middle latitude.

While this is true in general, for your specific case, could be some other reasons that can explain the anomaly, not necessarily related to the SSW.

In your first question, you want to know if the SSW can be regarded as the main cause for anomalous weather..Although it is highly probable that the SSW played some role, I believe that in the nonlinear system it has a very little sense to ask for main cause..

We found some connections between Major SSW occurences and temperature at surface in south of France (http://onlinelibrary.wiley.com/doi/10.1029/2012JD017631/abstract), and still this winter shows 16 days fluctuations in relation between ground and the stratospheric behavior (http://www.pole-ether.fr/etherTypo/fileadmin/files/SSW-2014-2015.pdf).

However, I agree with previous comments the challenge consists in understanding the causality; maybe quite complex.