GFS and GFSP are now moving the trop. vortex all the way to the other side of the pole days 12-16. They both shut down the Canadian vortex as should be the response. Yet with the exception of the GFS 06z op run, a flat pattern continues to work against the development of high-latitude blocking. As for that GFS 06z, it's still got a long way to go at day 16.
A persistent Euro High is a problem on most of the recent GFS runs. With this in mind, the 00z ECM ensemble spread is of interest:
Here, the greens and yellows represent a greater range in 500mb heights across the ensembles.
Because the low heights associated with storm systems tend to be more compact and less predictable, they tend to be responsible for a lot of the variation in these charts.
So what the above shows is a wide spread across the UK that covers anything from a trough diving down just west of the UK on a course for Europe to one heading north of Scotland and then on to Scandinavia.
The 00z operational ECM run dives the trough across the UK and manages to deposit a shallow trough around Italy. That's on the limit of the spread of ensemble solutions so odds are it doesn't make it quite that far, but any progress into Europe in the 9-12 day timeframe will tend to favour a Scandi/Russia ridge over a Euro ridge.
GEM shows the same idea but GFS and GFSP both delay such development until after the northern arm of the jet has established a strong flow over the top of the ridge, at which point you're left waiting for upstream amplification to change the game. You can see in the GFS ensemble spread that they are also more in favour of the flatter pattern than the ECM ensembles, though it can be seen that at least one GEFS member has that trough near Italy:
Overall then, a mostly westerly component to the flow in the 8-12 day range has very strong support, with some potential for a brief northerly, perhaps even veering easterly for a time, if we get the trough motion into Europe and enough of a break in the train of Atlantic storms.
As for going forward from there, the middle ground of the diving trough/flat jet options is basically inconclusive so all we can do is wait and see!
Edited by user
01 December 2014 13:33:45
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