would say that's boils down to the sheer matter of probability.
The governing algorithms will have a set of values that influences synoptic probability, in much the same way that you'll need to instruct an algorithm as to how the Earth rotates on its axis, and therefore what the prevailing (W~>E) pattern is. There'll then be thresholds which adjust prevailing probability, based on phenomenon such as SSWs.
However, I think understanding of SSWs themselves perhaps isn't established enough yet. In order to accurately mathematically model, using computational fluid dynamics, you'll really need to be quite sure of the data relationships involved, as - in an algorithm - if there's a high degree of doubt, it'll exponentially spoil. I would imagine that the boffins at Reading (ECMWF) are busy running developmental code, which would layer phenomenon such as SSWs into the operational algorithm. But there really does need to be a lot of research done into cause:effect, before you unleash a variable which - potentially - is very influential.
I wouldn't say it's so much a matter of money, but more a matter of scientific knowledge and geophysical understanding. Some of these relational processes and phenomenon are relatively new, and it takes time to carry out the proper audit of their scientific plausibility. What is important though, is the supercomputing ratio between Operational and Development. My understanding is that ECMWF are really exhausting their Developmental capacity, as Operational introduces more and more variables - net result being: less time to test and develop code. Ideally, you'd want a 70:30 ~ 80:20 split, but apparently it's now at a fairly critical 90:10.
All of that points to a fairly major upgrade in supercomputing power in the very near future, and - considering the high degree of success of ECMWFs NWP models - they make a very strong case for it. The JMA invested a staggering amount of money recently in a new supercomputer, and that's partly as to why UKMO have a high degree of respect for them, aligned to the fact that it runs the UK-UM base platform. The next UKMO upgrade is circa. 2015, and I wouldn't be surprised if there was even closer tie-in with ECMWF when this comes about.
Hope that's helpful?
SB
http://forum.netweather.tv/topic/75497-winter-model-discussion-06z-100113/page__st__160
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