David Morse

The ECM trend for Monday 12Z is more progressive now with bringing the cold in quicker

A few days ago the GFS was suggesting an easterly beginning on and around the 19th Feb, but the 12z has it now pushed out to the 23rd, a week later. I thought it be interesting to see what the trend of both ensembles was...

For a long time I couldn't get to grips with what it means and most explanations, including the MetOff, just say its a reversal of winds high in the stratosphere, which of course is true, but doesn't explain it really. So analogy time, this is how I understand it Imagine the polar vortex is a cup of tea and you are stirring it carefully to get the most perfect stable vortex going, as you stir faster and faster the tea moves higher at the edges of the cup, lower in the middle. This well in the middle surrounded by higher tea on the edge of the cup equates the to pressure differential in the Polar Vortex, low pressure = cold, so the centre of the vortex is the coldest place as it has the lowest pressure. The spoon represents the polar stratospheric jet stream driving the polar vortex. Your hand is chaos. As with all jet streams they're prone to speed up, slow down and at times buckle when pushed. So you're stirring your tea and someone knocks your hand. The jet stream (the spoon) deviates from its course around the cup and cuts into the flow, this disrupts the vortex. If the spoon is deviated enough the vortex stops spinning, the well at the centre fills with the tea from the outside and the pressure in the centre rises, high pressure = higher temps. It warms up.

Not really a model, but I was wondering people's thoughts on the QBO; I went through it to see which years looked similar to 2017 in the whole set and only three have a trend to easterly QBO beginning in late spring.

Perhaps the ECM and GFS runs are not giving enough to talk about; but its a clear extension of the blocking regime and it is ONLY the end of November?

Not surprising to see the 12z GFS revert back to a more cold theme from this morning's 6z which shows that the operational run was the outlier.

A bit pessimistic there non? Considering that so many teleconnections and indexes are pointing towards a colder than average start to the winter? Even the MO is saying there is a 30% chance of seeing cooler than average temps, 70% chance of average. Perhaps it'll not be 2010, but we'll all see snow falling at some point if not settling? To me all the recent runs are developing a theme and that is blocking and easterly and very little sign of any zonal coming back into play with any strength?

Isn't this all the response from the previous Strat. disruption about 12 days ago?

The February disruption in the QBO looked like putting the spanner in one of the possible cold influencing factors of this winter, here's a recent paper published on it, unfortunately its not accessible in full without an "institutional access" which I don't have. I think it is of great interest for those with a liking for cold (me included as I want to see a big freeze on the veg patch to get rid of this year's slug plague) with Siberian snow cover advancing very quickly in early October, increased late hurricane activity and what should have been an easterly QBO phase, what effect this will have on the potential for a colder than average winter. If anyone does have an OpenAthens type subscription, I'd love to see the whole paper. http://science.sciencemag.org/content/353/6306/1424

LOL thanks for the re-assurance; but I'm really not interested in the UK at the mo its the Alps I'm looking at. As regards the surface temps, wouldn't they be massively influenced by the increasing insolation? Therefore the average is bound to rise. In the graph you've posted its clear that on the 18th March there could be a diurnal difference of 14C so the average is a bit mute. I still think this early spring has a kick in the butt for many in the next two weeks and I'm just looking for great Ski conditions in the north western Alps.

I can clearly remember an early Easter in March in the 1970's with three foot of snow on the ground in Cornwall; it's not impossible. One of the other things I've noticed and posted on is the total flip flopping of the models and particularly the apparent zonal bias of the GFS which shows the retrograding the HP only for it suddenly to be swamped by a dramatic return to zonal. ECM 00z seems to be delivering a much more stable retrograding of the high with the continent getting colder every run, and more consistent than the 12z runs. Look at the set of runs below for Saturday March 19th, it certainly looks to me that the 00z runs are more consistent showing a retrograding of the high and encroachment of the cold?

Just not buying this from the current GFS 12z run, the high is retrograde right up to the moment the model starts to move into FI land and then the GFS sends it back east and packs in the zonals (just like its been doing for the past couple of runs)...yet we've seen time and again how the GFS over eggs any continental cold being displaced by the Atlantic only to correct at a later. I really think they're struggling with the SSW migration down through the atmosphere.

Looking at the 12z ECM run over the past three days for midday 17th March it's clear that the cold is progressing both south and west across Europe, so its not so far fetched to think it can't keep going and make its way to southern UK or further.

The GFS has been flip-flopping in the FI between a very cold scenario for western Europe and very mild, but the NOAA 500mb anomalies keep the HP over the Northern UK which means we may not see the cold here, but its looking more likely that Europe will have an icy blast.

@chionomaniac @phil nw. I see for support of my SSW claim I should have just brought in Judah Cohen: