Ik vond dit nog een aardige analyse:
http://forum.netweather.tv/topic/74751-model-output-discussion-12z-18102012/page__st__440#entry2387035
Today's model output is showing some interesting changes in the mid to long-term. There is now a reasonable consistency up to 5 days but thereafter, the signals are mixed.
Two things of interest that I think will have a bearing on the longer term trend here. First, the NCEP discussion from this morning:
"THE BIGGEST TREND IN THE MODELS SINCE YESTERDAY IS TOWARD A DEEP CYCLONE OVER THE GREAT LAKES MID FORECAST. THIS SPRAWLING LOW IS THE SURFACE REFLECTION OF A SHARPLY AMPLIFYING UPPER TROUGH, WHICH WILL HELP TO DRAW ARCTIC AIR INTO THE NORTH CENTRAL STATES. THE BAROCLINICITY OF THE EVENT WILL MARK A PATTERN CHANGE FROM THE CURRENT ONE, WHERE MOST OF THE NATION IS AWASH IN PACIFIC AIR. THE MAGNITUDE OF THE AMPLIFICATION AND THE TILT OF THE UPPER TROUGH WILL HAVE GREAT BEARING ON THE FATE OF THE TROPICAL LOW OVER THE CARIBBEAN."
So, we have a significant development over the US which does, I think, suggest a much higher likelihood of longer term blocking plus we now look likely to see some late season tropical activity acting as something of a wild-card. The NHC haven't called this tropical system yet but are giving it a high-probability of becoming a tropical storm in the next 24-48 hours. What this might do, assuming it does develop, is to follow the path of most of the storms this year and push a lot of very warm air up the US east coast, which in turn could significantly affect what happens downstream.
1) It might push a warm upper ridge well north towards Greenland and sharpen the downstream trough over us, or,
2) It could influence the jet and increase baroclinicity so much as to bulldoze its way through any blocking pattern and return us to zonality once again.
Secondly, I think the main model differences in the mid- to long-term is how each model is dealing with any polar front features running SE towards us that I referred to yesterday. Both the ECM and GFS and making more of this than previously, and the UKMet at T72 seem to be suggesting the same. All this will clearly affect the extent and duration of the cold air influx.
In spite of the above, on balance I still think we are headed for a significant blocking setup, with unusually cold air arriving later in the week, I say this mostly on account of what is now happening in the US and Canada, but notwithstanding what any tropical storm effect there might be to disrupt this.
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