David Morse
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Posts posted by David Morse
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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...
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35 minutes ago, timboy666 said:what is a ssw?
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.
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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.
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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?
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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.
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1 hour ago, Bristle boy said:
Agreed. Same as almost every Winter. Charts 10 days out seldom come to fruition. Winter will ramp up in the 'usual' way for UK come December. (Gut feeling)
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?
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3 minutes ago, Gael_Force said:
Is this not just a response to the strat vortex repositioning deeper into eastern Siberia. There is almost, if not quite, a reversal forecast. Another chance for the GIF as it shows the circulation going anti clockwise round where the core of the vortex is forecast to be
Isn't this all the response from the previous Strat. disruption about 12 days ago?
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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.
QuoteAbstract:
One of the most repeatable phenomena seen in the atmosphere, the quasi-biennial oscillation (QBO) between prevailing eastward and westward wind jets in the equatorial stratosphere (approximately 16 to 50 kilometers altitude), was unexpectedly disrupted in February 2016. An unprecedented westward jet formed within the eastward phase in the lower stratosphere and cannot be accounted for by the standard QBO paradigm based on vertical momentum transport. Instead, the primary cause was waves transporting momentum from the Northern Hemisphere. Seasonal forecasts did not predict the disruption, but analogous QBO disruptions are seen very occasionally in some climate simulations. A return to more typical QBO behavior within the next year is forecast, although the possibility of more frequent occurrences of similar disruptions is projected for a warming climate.
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
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1 hour ago, IDO said:
I would not worry about the ECM D8-10 op charts. Again the mean suggests 5-6c higher uppers at D9 compared to the op for the east of the UK. In fact the mean for GFS and ECM are not that far apart for 2m temps from D10-15 so I wouldn't expect any incoming cold on the current mean output:
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.
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1 hour ago, Frosty. said:
To be honest, if anyone is still trying to talk up the chances of significant cold weather occurring, it's just going to sound more and more ridiculous for that to happen at the end of March and first half of april and even though I'm a bitterly disappointed coldie with how winter turned out, I am looking forward to increasing spring warmth now the sun is getting higher and stronger with each passing day!
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?
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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.
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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.
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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.
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@chionomaniac @phil nw. I see for support of my SSW claim I should have just brought in Judah Cohen:
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WWN POLL: Should We Also Start Naming Heatwaves, To Get More Of Them?
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5 minutes ago, JOPRO said:
Good News, Looks like an early spring is due for the US could this help us get some cold weather in to the uk? However not certain how accurate this model is.......???
http://www.dailymail.co.uk/news/article-3427649/Pennsylvania-groundhog-set-predict-winter-ends.html
LOL I was asking the same thing and apparently Punxsutawney Phil is worse than flipping a coin, he has only a 47% accuracy on predicting an early spring, which is slightly better than his 36% accuracy on a long winter. I'm sure we are headed into a cold end of Feb and a cold March.
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After a very warm period in the western Alps, it looks like things are getting back to normal with some long range forecasts giving up to two meters of snow in the Portes du Soleil! Yippee!
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Nacreous clouds seen over Dublin this morning :-)
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2 hours ago, phil nw. said:
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GFS 12z 384hrs clearly shows the start of a wave 2 event IMHO.
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5 hours ago, phil nw. said:
We have seen quite a lot of w1 warmings at the top for some time and indeed a displacement is now underway but as i understand things we are not yet seeing a technical SSW as there is still no reversal of zonal winds forecasted at 60n at the 10hPa level.
Yes there has been some persistence of W1 warmings; but I have not seen ALL winter long the temp go higher than -30? Anyhow isn't what you're saying a little chicken or egg? The "technical" aspect of a wind reversal only occurs after the warming event, not before it, you need to see this level of incursion before the reversal of the winds surely?
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From some of the comments above I'm not sure what people were expecting an SSW event would look like :-)
Really, what we have in the GFS forecast is as clear a SSW event that you could get in my view. The GFS is showing a peak temp of -15C on the 6th Feb, an increase of 30C in a matter of 36 hours. Furthermore at 384 hours out it sunders the Strat PV in two on the 06z GFS run.
Isn't this what everyone's been looking for all winter long? :-)
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2 hours ago, Vorticity0123 said:
As can be seen here, in a region ecompassing the east of the UK and the northern parts of the Netherlands, temperatures are below -80*C, which might result in polar stratospheric clouds becoming visible just after sunset (so around now
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I've seen Noctilucent clouds in Dublin, but on in the summer; similar but perhaps not as colourful?
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On 26/01/2016 at 5:48 PM, bluearmy said:
that displacement isn't great for nw Europe unless it manages to force the jet far enough south to leave us under the extended broad vortex (v unlikely)
more probable is that the warming continues to push the vortex around broadly to the position it occupies around T240 but with the main warming on the Canadian side
then we have to hope that the Canadian vortex is less well positioned to keep the PFJ flat across the atlantic and that a mid atlantic ridge can form.
all the above assumes a trop/strat coupling which, whilst absent in early January, seems to be establishing thanks to the strong upsurge in zonal flow downwelling at the moment
Hi @bluearmy I'm sure that the location and position of the displacement is not reflected directly in the trop? That the effects are transmitted down and in the chaos the eventual outcome in 6 to 12 days after is not possible to model, particularly on how it will exactly effect the jet or the location of pressure cells? And as snow conditions over Ireland and The UK are always so marginal its impossible in my view to say that this is a bad set up or a good one!
Can you point to any examples which show the position(s) of a wave1 SSW event and how it always transmits into the trop?
If I follow the same logic you're employing, surely this set up would deflect the jet far south over North America and accelerate it north easterly over Iberia?
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Model output discussion - Post SSW - Will it turn cold?
in Forecast Model Discussion
Posted
The ECM trend for Monday 12Z is more progressive now with bringing the cold in quicker