Looks like ECM's catching on to what GEFS is showing. I think we might be a bit closer to knowing what the mid-term outlook is if this keeps up!
There are two likely scenarios on the table.
Before that, though, let's review what's going to happen. We already have a large upper ridge to our east, which is going to move northeast. This dislodges part of the vortex, which then becomes trapped to the south of the upper ridge (due east of us). Underneath this is some bitterly cold air, however it looks unlikely to affect us directly (there's still a tiny chance, but that's all it is - tiny!)
Some of the upper heights remain to the north of us, then attempt to "leak" back westwards. The majority is going to head away to the east, but the remnants, the leak, whatever you want to call it, will impede the progress of the next chunk of vortex which is moving eastwards from Newfoundland. There are two likely scenarios that follow.
One: the upper heights aren't sufficient to stop the jet and the Newfoundland chunk of the vortex from setting up shop near Iceland. This would lead to the jet roaring north of the UK, encouraging (eventually) increased heights over mainland Europe and bringing a return of mild SW'lies for the UK. This was shown in last night's 12z ECM.
Two: the upper heights are strong enough to force the upper low and jet further south. This means wet and wild weather for us, but crucially it means the heights "slip over" the low and end up west of Greenland. This gives an opportunity to link up to any ridges coming out of Canada and thus form a block - it doesn't look like this morning's ECM is going to do it, but several of the GEFS ensemble members do it, as does this morning's GFS. (Look at 240 - the ridge is amplified by the remnants of heights that have moved westwards over Greenland).
This is what GEFS is picking up on today, as has GEM to an extent. ECM is also showing it, but what differs is the phasing of the remnant heights and the next ridge moving away from the Americas. If the two phase, we get a potent northerly. If not, we get an extended spell of wet and windy (but not especially mild, at least by day) weather. And if not enough of that upper ridge makes it west across Greenland then we go back to default SW'lies.
Who said model watching was boring, eh? (And look, no need to mention the MJO, the QBO, AAM and so on!)
EDIT: Here are some annotated charts from the ECM run. The red arrows show the movement of upper heights.
T+72 - most of the heights go east, but a ridge heads west.
T+120 - ridging extends across Greenland from the east. That weak upper high north of the UK has nowhere to go!
T+192: the upper high gets ripped in two. Part heads east, the rest continues its journey over Greenland to emerge near Canada.
Originally Posted by: Retron