Winter Model Discussion 18Z 19/1/13 onwards.

[Catacol]

Blocked patterns do tend to repeat - that is something I have seen happen so often in the past - so I put my faith in that observation this time around!

You know much more than I... but the other lurking frustration with this winter is that we havent really seen any proper blocking. Anomalies have suggested it, but we have been in the back pocket of the Canadian Vortex most of the winter, with nothing more than the current deflections to write home about. GP got my hopes up in November with talk of high lat blocking, negative NAO along with the negative AO and a particularly blocked late Jan/early Feb. Right now I cant see where it is going to come from precisely because of your comment on winters tending to feature repeating patterns. I see another week or two of atlantic dominance followed perhaps by height rises over Canada encouraging a potentially early spring.

It has been an interesting winter of cold zonal so far overall - that didnt worry me too much in the early stages as for the SW that suggested big snowfall... but that has not happened. Seems we need to have a big block in place after all to get the really cold air in place first. This marginal stuff is just... well... too marginal. Quite why there was so little precipitation on Friday after the absolute drenching the SW has had from every other front that has been inbound this winter I dont know. It wasnt that it rained - it just didnt snow enough. Guess that was just back luck.

Back to my reports. Wish they were as fascinating as interpreting hemispheric weather patterns!

Edited January 20, 2013 by Catacol_Highlander

[TheHumph]

There are many odd features to this present cold spell, not least of which is that it isn't actually that cold! Seems an odd thing to say but the thickness values have been hovering around 528 throughout, unlike say 2010 when they got down to 516 and below - that IS cold. But, all credit to the Met for the accuracy of their snow distribution forecasts.

Come to think of it OMM you're right! Although it has been snowy and we have had the odd frost, it hasn't been that cold - something that really hasn't crossed my mind.

Not as cold as 1963 I bet! I posted on the SW/C England thread that I was born in April 1963 and that my mum would have been heavily pregnant throughout that winter. I can't even begin to imagine how she coped - how anyone coped!

I'm no expert on blocked patterns but I will bow to your greater knowledge and use it as a further straw to clutch!

[OldMetMan]

Oldmetman, how much snow did the s.w actually get back then? Thanks om.

Hi offerman, I have just done a quick post of my own experience of it, but snow drifts of 20 - 30 feet occurred and cars, trains etc were literally buried, especially over places like Dartmoor and Exmoor.

[Dunstable Snow]

With all due respect, credit where credit's due Matt Hugo has provided a great insight past where we can only dream of venturing. He has access to ECM 32 day and provides great valued information to us.

Obviously it's not nailed yet though, nothing is during this time. South Westerly/Westerly might be a massive snow event also and this could change to something like 1963 where the cold fights back and provides us with a good dumping. Snow reflects 85% of UV radiation, so it's going to be quite hard now for the Atlantic to just win...

Models might be showing exactly what they where showing one week ago. This is last week's 18z for today 1900z

And this is the actual chart...

Support or no Support, this is the 18z chart for today. Go figure....

Let's see if this chart verifies exactly for next Sunday, as it doesn't look too dissimilar to the 13th's 18z...

Fully agree with your points and this is far froma done deal. There is one major difference now compared with this time last week and thats the raw UKMO output. This time last week it was leading the way with the undercutting low pressure through the English channel. GFS and ECM were firmly in the breakdown to westerly camp and the met office fax significantly modified the UKMO raw IIRC. Over the last couple of days we have seen UKMO raw lead the way again on this breakdown at a time when GFS and ECM have been fluctuating all over the place. In my view we need to see positive changes and quickly with UKMO leading the way if this is not going to happen. I do understand a lot of peoples concerns over where we might end up if the breakdown comes as progged but, as others have stated, some short term pain might well lead to a memorable February ( from say seconfd week onwards) if the blocking set up is right. Lets hope so... In the meantime I am now into my 13th hour of non stop snow within my third major snow event of the last seven days.. Not bad eh ?!

[offerman]

Old man met, i remeber 1980s winters and they were pretty bad , well good.

There is a heavy band of precipiation off cornwall at present and at the moment this doesnt look like just skirting with southern most cities on south coast as forecast for monday. Any chance that this could continue on its,current path and affect the whole of the southwest tomorrow?

[chriszoff]

I don't think the senior people on here massively ramped anything. They simply gave their opinion and explained the potential. It's other people who have taken those posts and ramped them to a point where I think some people were expecting something akin to The Day After Tomorrow. Unfortunately, if you come on here hoping to see something then whatever the outcome is you will always have a subjective view of it rather than an objective view. That tendency for a lack of objectivity is shared by a number of other members here and that filters through to their analysis. So we get the slightly childish winter is over posts a few weeks ago despite the fact we were only a month into it and obviously we now have a cold spell bringing some decent snow and cold to most of us. From what I can see the senior people on here don't fall into that category.

well i won't get drawn into a protracted debate on this but i suggest looking back through the winter discussion where you will see senior forecasters also bemoaning, we have had more snow here today which is great for me but it all still lacks bite and it looks like it's about to tail off at least for a while given latest output, i guess some members expectations are higher than others especially when comparing to the past as many posts are currently doing, never the less Winter is far from over so jury is still out

[offerman]

Omm, thanks for answering the depth question, wow, amazing times then.

Edited January 20, 2013 by offerman

[OldMetMan]

You know much more than I... but the other lurking frustration with this winter is that we havent really seen any proper blocking. Anomalies have suggested it, but we have been in the back pocket of the Canadian Vortex most of the winter, with nothing more than the current deflections to write home about. GP got my hopes up in November with talk of high lat blocking, negative NAO along with the negative AO and a particularly blocked late Jan/early Feb. Right now I cant see where it is going to come from precisely because of your comment on winters tending to feature repeating patterns. I see another week or two of atlantic dominance followed perhaps by height rises over Canada encouraging a potentially early spring.

It has been an interesting winter of cold zonal so far overall - that didnt worry me too much in the early stages as for the SW that suggested big snowfall... but that has not happened. Seems we need to have a big block in place after all to get the really cold air in place first. This marginal stuff is just... well... too marginal. Quite why there was so little precipitation on Friday after the absolute drenching the SW has had from every other front that has been inbound this winter I dont know. It wasnt that it rained - it just didnt snow enough. Guess that was just back luck.

Back to my reports. Wish they were as fascinating as interpreting hemispheric weather patterns!

I take your point certainly, it's not been spectacular! However, the flow as it has been recently has been anomalous. I base much of what I say in this regard from historical patterns rather than specific atmospheric indicators which I have to admit I know little about. However, I have seen a lot of weather and, as in other walks of life, one gets "gut feelings" as to what may happen, without necessarily having any hard evidence to back it up! Not always right, for sure but occasionally!

Anyway, good luck with your reports!

[Robbie Garrett]

Fully agree with your points and this is far froma done deal. There is one major difference now compared with this time last week and thats the raw UKMO output. This time last week it was leading the way with the undercutting low pressure through the English channel. GFS and ECM were firmly in the breakdown to westerly camp and the met office fax significantly modified the UKMO raw IIRC. Over the last couple of days we have seen UKMO raw lead the way again on this breakdown at a time when GFS and ECM have been fluctuating all over the place. In my view we need to see positive changes and quickly with UKMO leading the way if this is not going to happen. I do understand a lot of peoples concerns over where we might end up if the breakdown comes as progged but, as others have stated, some short term pain might well lead to a memorable February ( from say seconfd week onwards) if the blocking set up is right. Lets hope so... In the meantime I am now into my 13th hour of non stop snow within my third major snow event of the last seven days.. Not bad eh ?!

Come to think of it, the last chart for next weekend would require some corrections. Not as much as last weeks for this weeks to be another snow event from France. Let's wait and see

One thing for certain that is being overdone it the strength of that Vortex chunk over Newfoundland, it's been doing it for the last 3 bloody weeks and keeps giving us 940/950mb low's....

Edited January 20, 2013 by Robbie Garrett

[Tom D]

Come to think of it OMM you're right! Although it has been snowy and we have had the odd frost, it hasn't been that cold - something that really hasn't crossed my mind.

What?! I know what you're saying is that we haven't seen exceptionally low temperatures, but here day time maxima have been 0.8c or lower for all of the past 8 days, including today, where it's been sub-zero on three of those days and overnight on Tuesday we saw -9c.

[OldMetMan]

Old man met, i remeber 1980s winters and they were pretty bad , well good.

There is a heavy band of precipiation off cornwall at present and at the moment this doesnt look like just skirting with southern most cities on south coast as forecast for monday. Any chance that this could continue on its,current path and affect the whole of the southwest tomorrow?

The cyclonic circulation is quite complex at the moment with today's LP gradually being absorbed into a developing LP to the SW. It depends where you are located as coastal areas will I believe still be marginal. I would be inclined to carefully watch what subsequent LPs develop upstream in the next few days heading your way. Particularly keep in mind wind direction - any switch to an onshore flow as opposed to what we are getting now could make a very big difference as to whether it's snow or rain.

[TheHumph]

What?! I know what you're saying is that we haven't seen exceptionally low temperatures, but here day time maxima have been 0.8c or lower for all of the past 8 days, including today, where it's been sub-zero on three of those days and overnight on Tuesday we saw -9c.

Day time temps in and around Petersfield have been in the region of 2c-5c. Below average yes, but not with that bitter feel. It maybe the winds haven't been that brisk or the fact we're located not too far from the sea. Night time temps haven't been extravegantly cold either.

I'm not saying it hasn't been cold in other areas Tom and it has been a great couple of weeks. Ironically it is forecasted to be -5 here tonight!

[OldMetMan]

What?! I know what you're saying is that we haven't seen exceptionally low temperatures, but here day time maxima have been 0.8c or lower for all of the past 8 days, including today, where it's been sub-zero on three of those days and overnight on Tuesday we saw -9c.

What I was saying relates to thickness values which have been around the threshold where one starts talking about snow - 528dm. I'm not denying the low maxima and minima that have occurred.

[chionomaniac]

Latest NAE for tomorrow evening. Those in Scotland and the SE may be interested.

Edit and lo behold Cork!!!!

Edited January 20, 2013 by chionomaniac

[Mr Frost]

Reasonable grounds for thinking that the global synoptic dynamical model is moving towards a third cold pattern this winter (the waning of this present one being well advertised) and the last few GEFS ensemble means have leant support to this idea.

Tropical convection has been focussed in the western Pacific in the last 10 days. This has introduced anomalous westerly winds to the tropical Pacific which in turn has helped lift tendency in angular momentum towards an El Nino type pattern.

Latest TOA Triton data indicates anomalous ocean heat content centred just west of the Dateline and encroaching anomalous westerly winds on the back of the MJO. Trade winds are also decreasing, which is typical of MJO progression towards phase 7/8.

The GEFS MJO forecast has come to life in the last day or so, suggesting a strong amplitude wave to develop in phase 8.This seems reasonable on the basis of favourable conditions for convection due to increased heat avalability and cooling upper atmosphere (especially lower stratosphere).

These tropical developments are beginning to take effect in the sub-tropics. A strong +ve mountain torque has occured and tendency in angular momentum is already postive and likely to spike very positive in the coming days. Overall relative angular momentum similar to November.

The shrewd will recognise that the last uptick in relative angular momentum heralded our first pattern change and cold trough in December, by about 2 weeks lead time as positive (westerly) wind anomalies are fluxed poleward introducing anomalous mind and high latitude ridges and circumglobal troughs (Pacific and Atlantic).

Meantime, our first downwelling wave from a very strong polar stratospheric warming (and sustained reversal in zonal winds) has matured. Stratospheric time scales are extremely long, and we can expect further downwelling episodes lower down in the atmosphere for the next few weeks. Based on Baldwin'c composite of weak vortex events, the next episode of increased eddy activity is due around 28th January although the timing of this is not exact.

The temperature anomaly section shows a reasonable time scale for 'nodal' type propogation extending into February, perhaps more towards mid February. A typical tropospheric response to this would be very similar to an MJO phase 8 projection, so its interesting the atmosphere choreographed in this way.

So teleconnectively we have a reasoned case for anomalous heights to our north end January into February. The timing of this highly problematic as the models were to a degree blind-sided by the first downwelling wave, only latching onto it 2 days before the warming took place. Were this happen again, a sudden turnaround in modelling could well occur.

The last five GEFS mean height anomaly for the extended range has 'hit the target' on all five occasions to varying degrees, which is interesting in itself. Todays GFS super ensemble mean height anomaly....

Putting this together, expect further cold pattern, becoming stronger probability the further we go into February but I wouldn't be suprised to see it pop up from 28th January onwards. Winds from the NE and E the favoured scenario.

Copied from In depth discussion thread.

A GP special for the coldies!

AVE IT!!!

[Polar Maritime]

Well Im very happy with the cold spell so far, the last 4 days have been ice days, I have 22cm of level snow outside, with drift's up to 1m+ out in the fields and snowing now, FI is +96hr, I really don't think we are going to just jump to zonal as easy as is being model'd out in FI.

Edited January 20, 2013 by Polar Maritime

[-uksnow-]

@Chiono - Is that not the 12z NAE you just posted..?

[weather eater]

It is actually quite straight forward what is being modeled on the hemispheric scale.

We have had a large SSW that has displaced the PV to the Atlantic side with a large ridge based on the Pacific sector. Following this, the Atlantic PV has been cut in half leaving the two vortices seperated but still based towards the Atlantic sector. Further upper warming is destroying the stratospheric Canadian vortex but leaving the tropospheric vortex intact. The underlying upper Pacific ridge is maintained whilst the tropospheric Canadian vortex tries to join with its Siberian counterpart, thus removing the small wedge of increased strat and tropospheric heights keeping them apart.

Meanwhile, the Siberian stratospheric vortex (10 hPa) will slowly increase in strength and eventually make its way back to the pole (over the next 2-3 weeks). What occurs to the tropospheric vortex during this timeframe is unknown, however we know that its starting position is Atlantic based and that the tropospheric vortex is unlikely to regain full strength for a long time yet, and, as the upper Pacific ridge wanes so will the lower Pacific ridge, allowing heights to build elsewhere tropospherically at high latitudes. We don't know where yet.

You do realise that your post sounds like a plot from Eastenders don't you.

[chionomaniac]

@Chiono - Is that not the 12z NAE you just posted..?

oops sorry, the snow is going to my brain - and I don't like the updated ones!

[John Cox]

Edit and lo behold Cork!!!!

It never snows in Cork

I think this time January Snowstorm will be pleased.

Well at the moment the Extra Radar shows sleet approaching Cork but hopefully it will turn to snow

[damianslaw]

Right now its a very complex set up with a complicated low pressure cell to our SE and a developing shallow feature to our SW with trough and frontal features wrapped around both features - tracking where these will end up is quite difficult, hence the BBC forecasts being quite generous with there sprinkling of snow in no cohesive fashion.

All the models agree on the cold staying until Friday, by Wednesday we will come under the influence of a slack airstream, which could mean freezing fog and probably much clearer skies, Thursday and Friday in England and Wales in particular could end up very cold days indeed with severe frost.

GFS, ECM and UKMO are all suggesting a breakdown from Friday onwards starting in the NW first, but enveloping the whole country through next weekend, it could end up a slower affair, but the energy coming from the weakening and moving Canadian vortex does look preety strong.

Longer term - the upstream signals suggest a shortlived less cold and I use the word less cold - not mild, spell of atlantic weather as we see the canadian vortex smashed and its energy ejected into the atlantic, in time once we squeeze all its energy away we will likely see mid atlantic height rises and with strong heights over the arctic - these will have a very easy time in linking together over Greenland. I'm not concerned about what the models are suggesting for the end of January in terms of future cold snow prospects, it is necessary in order to deliver our next round of cold and snow, next time from the NE.

[Rocheydub]

It never snows in Cork

I think this time January Snowstorm will be pleased.

Well at the moment the Extra Radar shows sleet approaching Cork but hopefully it will turn to snow

We have nowt to be pleased with here in the capital either John. Very marginal again tonight, despite the ME warnings. I'm in north suburbia, we missed out by a few miles today...

Back to the models, good agreement at present that we will see a more SW influenced pattern later this week rather sadly, however, things have a will change in the short term... I keep the faith and as with GP's post copied above, I will follow the MJO and other charts rather more closely in the next few days...

[Tamara]

I admit I might want a few extra days to play in the current snow when time allows me, and fingers crossed there isn't too much of an early thaw, but I also think that we can spend too much time looking ahead for the next cold spell without enjoying the current one. It is wonderful out there atm and the models were not in agreement about this weekend/today/tonight in advance a week ago. So a bit of manyana might be a good thing

[ribster]

MattHugo81

Every single ECM ensemble member has an unsettled W or SW'ly flow over the UK by Mon 28th with just differences in position of low to the NW

20/01/2013 20:32

MattHugo81

EC ENS mean supports the EC model out to 240hrs with a dominant low to the NW of the UK and a W or SW'ly air flow over the UK.

20/01/2013 20:29

Pretty much nailed on then.

Not according to Alex Deakin it isn't, he said on the forecast take what is showing for the weekend (in terms of a pattern change) with a pinch of salt, if not a gritter load of salt!

[Djdazzle]

Not according to Alex Deakin it isn't, he said on the forecast take what is showing for the weekend (in terms of a pattern change) with a pinch of salt, if not a gritter load of salt!

He's probably been looking at his seaweed . . .

It's a brave call to go against such strong model agreement.