Winter Model Discussion - Cold Hunting -23/12/12

[Methuselah]

It looks highly likely to occur now, since we have cross model agreement and have had for a few days...

I do hope that doesn't become NW's answer to a football manager's 'vote of confidence'!

[ChartViewer]

I do hope that doesn't become NW's answer to a football manager's 'vote of confidence'!

As long as Gareth starts to behave

[Dean E]

On the radio 4 weather forecast from the BBC early'er, they said January will get colder.

Things are starting to look good.

Oh dear, If the BBC (Met Office) agree, its going to be Atlantic driven! Obviously I joke, the Met Office always get the stick pointed at them when things change (Barbecue Summer for example). Its not their fault obviously, its just how the UK is! Varied!

Anyway, enough of my ranting to myself... SSW seems quite likely now cross modelled agreement. 500MB Charts are the one I'm keeping an eye on over the next few days as the models react to this.

SM

[nick sussex]

A good ECM this evening and far different from its earlier 00hrs run, it had a similar set up a few days back but then dropped it but taken at face value it certainly shows a way out of the current pattern.

Theres a good amount of energy going south and with pressure rising to the ne you always have a chance of something developing.

I think low pressure developing over the USA could well hold the key to help draw some of the energy away from the Greenland area and if its sufficiently amplified could sharpen the low to the west of the UK.

So something like this for newer members to look out for, its time for one of my paint jobs!:

Red circle -low pressure amplifies more

Black arrow- low heights get pulled further nw

Purple arrows- because the upstream pattern is more amplified this helps sharpen the low to the west, this elongates with more energy heading south

Orange arrow- pressure builds to the ne and ridges sw at the same time the low to the west disrupts and splits

So we could be saying goodbye to the mild and saying hello to colder conditions if my masterplan works!

At least we're seeing some opportunities opening up and with the slowing of the zonal flow even before the full on SSW whats to say we don't see more retrogression of the pattern.

You just never know with these warmings just how they will play out so we just have to sit tight and enjoy the ride and hope for the best.

[LomondSnowstorm]

I do hope that doesn't become NW's answer to a football manager's 'vote of confidence'!

Oh god no, please say I haven't jinxed the whole thing with that comment

[pipsta]

Good weather program on more 4 ATM. Is our weather getting worse

[alexisj9]

This thread can be so confusing at times for those of us with less expertise.

For example, earlier today, in the space of just three posts, the GFS 12z was described as :

1) promising for those seeking cold

2) a disaster for cold lovers

What chance have we got of learning anything given the above?

Sorry for the rant, but it can be so frustrating at times!

It does make it quite difficult, I tend to ignor all the it looks bad for cold posts as they should be in the moaning thread anyway, and just pay attention to posts that talk about what is in the charts, and the analisis that is provided. The fact is that the lastest run is bad for cold in the begining and then changes in fl. It's quite posible that someone jumped the gun before the run finished or doesn't pay attention to fl charts.

[phil nw.]

I believe the forecasted reduction in the mean zonal wind speeds (westerlies)higher up in the Stratosphere are now just starting to impact the daily runs.We can see this by viewing these ECM images from yesterdays data.The first is day7 and the other is day10

The blue colour is the reversal of the westerly flow and by just comparing the 2 we can see how the warming is causing reversal from the top propagating down to the trophospheric level and extending gradually south from the pole.

This will impact on the strength of the jet and allow any ridging High`s a better chance of building towards the Arctic with time as the effects are felt more and more.

As the vortex weakens we naturally see height anomalies rise across the Arctic as seen on 12zGFS/ECM ens

Day 10 on both

and day15 GFS

Just to stress these are Ht. anomls. not mean hts and there will a delay before the Hemispheric pattern flips but they give a good idea of a weakening and eventually shredded vortex.

In the meanwhile the prospect of a mid-latitude UK High is a step in the right direction as well as giving the UK a break from the relentless rain.

[bluearmy]

Naefs 12z spreads pickup a sustained mid atlantic height rise post jan 13th and a mean upper ridge iceland to east greenland by T384. Lets hope that within a day or two, we'll be seeing a large mean greeny ridge on that model.

[Snowmad79]

I believe the forecasted reduction in the mean zonal wind speeds (westerlies)higher up in the Stratosphere are now just starting to impact the daily runs.We can see this by viewing these ECM images from yesterdays data.The first is day7 and the other is day10

The blue colour is the reversal of the westerly flow and by just comparing the 2 we can see how the warming is causing reversal from the top propagating down to the trophospheric level and extending gradually south from the pole.

This will impact on the strength of the jet and allow any ridging High`s a better chance of building towards the Arctic with time as the effects are felt more and more.

As the vortex weakens we naturally see height anomalies rise across the Arctic as seen on 12zGFS/ECM ens

Day 10 on both

and day15 GFS

Just to stress these are Ht. anomls. not mean hts and there will a delay before the Hemispheric pattern flips but they give a good idea of a weakening and eventually shredded vortex.

In the meanwhile the prospect of a mid-latitude UK High is a step in the right direction as well as giving the UK a break from the relentless rain.

Not sure I like those Phil. All well showing good heights over the pole but the euro height anoms look far more dominant in those charts... doesn't particularly fill me with new years joy! Lets say those anoms proved right.... Us poor westerners will be stuck in a wet Atlantic flow, NW SE split.

Edited December 29, 2012 by Snowmad79

[nick sussex]

Although these are just automated at weekends the NOAA maps are in good agreement with the trend of the ECM operational run:

6 to 10 day

8 to 14day

I'm liking this developing negative anomaly digging south in the mid Atlantic because if you add what Phil posted how much retrogression of the pattern could we see with the slowing and then reversal of the zonal flow.

Bear in mind Feb 2009, the hasty rewrite needed of the UKMO outlook because the models underestimated the reverse zonal flow impact.

I'm not saying thats going to happen here but theres no simple answer to the effects of a SSW in terms of initial quick response and timelag to full impact.

Edited December 29, 2012 by nick sussex

[Guest Kent-Weather]

PTB #14

12th Jan 2013. T850's and Z500 (T+366 - lol!) Given how dire for snow lovers it's been, I'm sure this would send a 5 mile long queue just for people to grasp at this single straw in hope. Usual pitfalls of course with the timescale and it being a single ptb but it's a straw none the less

[Frosty.]

Good signs of blocking beginning to develop on the Ecm 12z later in FI towards days 9 and 10 and a cooling trend, the yellow 850's being drained out with cooler T850 hPa on the way. As for next week, rather cold and unsettled at first with spells of rain and wintry showers, then turning milder from midweek through to next weekend with pressure rising from the south and the unsettled weather being pushed away to the north and some rain and breezy mild conditions becoming confined to scotland and n.ireland. As for the gfs, it's not onboard with the ecm idea and keeps a more changeable mobile pattern throughout for northern britain, more settled to the south with high pressure to the south and southeast.

[Great Plum]

Using the gfs 18z, here are the top temps for London over the next few days... (I am aware this is not foolproof!)

7, 10, 5, 5, 9, 9

Considering how mild it was forecast to be over the next few days countrywide, those are pretty average (slightly mild ) temps...

I am aware that the west is milder throughout as is often the case...

[Grimsby Snow Lover]

I know its not particulary cold but a very interesting chart non the less and would probably lead to another push of high pressure towards Greenland as in the 12z run.

http://cdn.nwstatic....372/h500slp.png

Edited December 29, 2012 by Grimsby Snow Lover

[Weathizard]

A Cool zonality finish to this run, however still good signs that the PV near Greenland is spent. I'm hoping to see some more positive ENS members to continue the trend we've seen.

[TEITS]

Hard to spot a trend in todays models when we see such different runs from the likes of the ECM. The same goes with the GFS because in F.I HP over the UK is replaced by LP.

This though is a positive trend for me. The most disappointing aspect of the xmas model output has been the consistency of mild, zonal runs. Now we're starting to see quiet significant changes between runs which in my opinion means a pattern change is going to occur.

So over the next few days I would be wary of the model output until we spot a trend. Probably best just to look at the ensemble mean for the moment.

[snowking]

Well despite the nonsense being churned up at the surface swinging wildly from run to run, we maintain the consistent theme of a secondary warming centred around Greenland:

And before anybody tries jumping in suggesting its just staying at +384:

So that we can keep note, the 12-13th has been the suggested date of the start of this secondary warming, the relevance being that this may help to induce a quicker tropospheric response around a week from that date of 13th Jan

SK

[bluearmy]

Gfs fi seems not to have a clue what to do with the sudden lack of zonality! Expect lots of chopping and changing over the next few gfs fi runs as the model tries to resolve where not to put the energy! starting to look ominous for those who have written the winter off.

[Tim Bland]

Nice to see signs of the PV fragmenting and pushing west! Could be very snowy for high ground in the north if this came off and a northerly would follow http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=384&mode=0&carte=1

Lots of chopping and changing run to run, but as Teits says this is good news because frankly any "change" is welcome. GP seems confident of a pattern change that will please us coldies by the end of Jan.

Edited December 29, 2012 by Tim Bland

[Glacier Point]

Well despite the nonsense being churned up at the surface swinging wildly from run to run, we maintain the consistent theme of a secondary warming centred around Greenland:

And before anybody tries jumping in suggesting its just staying at +384:

So that we can keep note, the 12-13th has been the suggested date of the start of this secondary warming, the relevance being that this may help to induce a quicker tropospheric response around a week from that date of 13th Jan

SK

Indeed Kris. The residual vortex is basically ripping the upper level westerly circulation apart indicative of a reversal of the mean flow across much of the polar field. The trop PV on the 18z op becomes very constricted and shiftward south and west as the upper level changes occur before emptying rapidly. Fun times ahead.

Edited December 29, 2012 by Glacier Point

[johnholmes]

This thread can be so confusing at times for those of us with less expertise.

For example, earlier today, in the space of just three posts, the GFS 12z was described as :

1) promising for those seeking cold

2) a disaster for cold lovers

What chance have we got of learning anything given the above?

Sorry for the rant, but it can be so frustrating at times!

CS

You will soon pick up who gives objective views and who ramps up a chart for whatever their preference, be it cold or mild. For a pretty unbiased view of the models, usually 2x daily, read the post from Gibby, usually in the model thread and in the other supposed more selective thread.

Have a read of the Net Wx Guides on what to look for, how to use the GFS output to do your own forecast and lots more.

[damianslaw]

Sticking to the reliable timeframe first i.e. out to 3rd January, all the models continue to be in agreement i.e. azores high will ridge NE into southern britain on the 2/3rd Jan with low heights becoming entrenched to our NW - end product a mild but drier spell of weather. Before the 2nd, the north is actually seeing quite a typical early winter spell with classic tropical maritime air alternating with polar maritime air with marked warm and cold sectors embedded within the atlantic low pressure systems. Right now much of Scotland and just about far N England is sitting in sub 528 dam air - which is helping to pull in some quite cold uppers and evaporative cooling effects meaning wintry showers down to quite low levels, however by New Years Eve, the warmer uppers will be back, before another polar plunge on New Years Day and a return of the sub 528 dam air, so at least in the short term the northern half of the country is seeing quite an average spell of weather certainly not what could be described as mild. Central and southern parts however, will maintain milder uppers and consequently the mild theme continues.

As we head into next weekend, which is just beyond the reliable timeframe divergences between ECM and GFS unlike this time yesterday, with the former once again wanting to ridge heights further north blocking any quick atlantic onslaught, whereas the GFS is suggesting only very weak ridge development and the atlantic once again comes crashing in, but with much less intensity than the past couple of weeks, perhaps indicating a weakened polar vortex and consequently perhaps increased chance of amplification in the flow as we head through the second week of Jan aided by a more southerly tracking jet - indeed the longer range GFS outputs are suggesting much cooler conditions with much less of a flat pattern and therefore probably a buckled jet which would enable height rises to our north. This is all a long way off, but there is a stirring in the models today that they are beginning to respond to longer term northern hemispheric changes i.e. the polar vortex returning to a much weakened state after its brief spell of excitement over the festive period.

[ITSY]

based off my very limited knowledge of SSWs and the resultant emergence of one or two interesting offerings over today's runs, I would say that the second half of January or early Feb looks like the next best bet for cold. It will really be a waiting game now, but interesting times to track the development of the models as we seek out some long awaited cold (and of course snowy) weather.

Indeed, Matt Hugo agrees - see his twitter feed for more info, as it offers his view that a significant pattern change could develop from mid-change onwards.

Hopefully, I have provided the much needed straws. Clutch away.

Edited December 29, 2012 by ITSY

[EML Network]

I guess it's a little too early to be looking for any effects of a SSW on the GFS charts, but I still can't see anything even in FI that is going to deliver us any cold weather, surely by this time next week, we should be seeing some hints of something, all I can see for the foreseeable future is High pressure close to the South of the UK, meandering around and never really moving too far from N.France , if anything the trend seems to be to flatten the High pressure yet again with the Jet stream mid way through the run, being well North of where it should be at this time of year.

If we get to Mid January and we're still not seeing any beneficial effects from the SSW in terms of blocking being in the ''right place'' , then I fear for the remainder of Winter, from a cold and snow lovers point of view, we'd more than likely then be relying on the odd and all to brief cold snap or two at some point in Feb.

I think I am growing impatient now, I've been waiting all year for a cold Winter and thus far it's been a real let down, all of this being said I have a sneaky suspicion that the first 1/2 of March is going to be bone chilling , nothing to back that up other than we're overdue a cold March.