Model Output Discussion - 23rd Jan - 12z onwards

[weather eater]

I have to say as well, hats off to the GFS it has done really quite well with this spell, except for over complicating the LP for a time, it certainly picked up the slider low early.

 

The 06z after toying with an easterly has reverted to the idea of the MLB close or over the UK that we saw from a number of runs a couple of days ago, I still think this looks like the most likely solution with the possibility of a reload thereafter.

[Nick F]

06z GFS further east with Monday's low tracking SE across Ireland and the far SW, so risk of sleet/snow that bit further east across Wales and S England.

 

Conversely, the surface pressure trough moving SE tonight, bringing a more organised band of sleet/snow further west on 06z UKMO (Meso) as per 00z ECM and Euro4. GFS further east. So more organised sleet/snow pushing across N Ireland later today then spreading SE across Wales, Midlands, SW England - but uncertainty over how far east.

 

Saturday shows some interest too with one or two features running south in the flow bringing more organised bands of sleet/snow showers.

 

Goes to show how difficult these features are to forecast, even with 12 hrs lead time!

Edited January 29, 2015 by Nick F

[Captain Shortwave]

Interesting second week with the Atlantic high ridging into Scandinavia and then retrogrades back into the Atlantic, only to yet again push into Scandinavia. 

Cold out to day 10 with snow showers again pushing into some eastern areas at times.

[The Enforcer]

850 wet bulb potential temperatures are several degrees above freezing as we head into Thursday night, ideally you want these to be at freezing or below. Although the fact it is night-time will help as the precip moves southwards, and in any heavier bursts snow is certainly possible.

 

The 850s are at -5C DPs -2C as discussed two days ago, but the situation has changed in that WBFL now appears to be much more favourable with freezing levels down to below 100m even for here, yet rain is still being forecast for this period. So now what is stopping snow from falling?

 

http://expert-images.weatheronline.co.uk/daten/proficharts/en/2015/01/28/basis18/ukuk/thfr/15012921_2818.gif

[TEITS]

I know its the NAVGEM but an improvement compared to the 0Z.

 

http://modeles.meteociel.fr/modeles/navgem/runs/2015012906/navgem-0-144.png?29-11

[iamgazza]

The 850s are at -5C DPs -2C as discussed two days ago, but the situation has changed in that WBFL now appears to be much more favourable with freezing levels down to below 100m even for here, yet rain is still being forecast for this period. So now what is stopping snow from falling?

 

In theory - Nothing. I shouldn't worry to much. I have been pretty bullish to friends\family that anything that falls later today will be snow. I remain confident. MET now have us under a yellow warning for snow (mentions hail\rain too) The warning for later today was issued this morning, which indicates the headaches they are having with everything going on. Lot's to be positive about as we head into the weekend and into next week too.

[492]

In theory - Nothing. I shouldn't worry to much. I have been pretty bullish to friends\family that anything that falls later today will be snow. I remain confident. MET now have us under a yellow warning for snow (mentions hail\rain too) The warning for later today was issued this morning, which indicates the headaches they are having with everything going on. Lot's to be positive about as we head into the weekend and into next week too.

I have not seen any upper air ascents but I would imagine there is a steep lapse rate in the unstable polar air over the UK at the moment which will be conducive for precipitation to turn wintry once it starts.

[Kentspur]

Yellow warning alert- all areas except parts of southwest:-) and this time due to "SNOW" and ice!

[carinthian]

The GEM is a winter feast of epic proportions. Not out of the question but more than likely the extreme outcome. However, the GFS latest run reverts again and slows the Atlantic with blocking coming in the equation again later in the run. ECM could end up with a rinse and repeat of short mild Atlantic and quick return to cold. I still favour a blocking scenario to the East or Northeast in the longer term outlook towards Mid Month. Still the snow scenario beckons for the next 5 days for much of West Europe including the British Isles. Will have an update later this morning regarding our snow portal service information. Its outer perimeters may give some guidance for your part of the world.

C

A bit of a up date for you,looking specifically Mon to Fri next week regarding snow prospects in your part of the world. The discussion starting with the Low circulation forming off St Johns this weekend. Consensus is the GFS model has previously handled this type of development well in the past few weeks and tend to back its track towards the British Isles, possible later runs look it could send this a little further east. So Ireland and the SW England and Wales have a good probability of being affected by this development. Snow portal ratings of 30% not bad with scope for further upgrades and maybe be further east but not north. Beyond and into next week cold pool circulation developing over mainland Europe with snowfall probability high, this could impact into the Southeast of England, again medium snow prospect ratings as pressure will be rising further to the West and North. We are on the edge of perimeters for actual snow depth forecasting for your part of the world but index rating for some widespread cover looks fairly promising during nexts week cold spell.

c

[Nick F]

My latest synoptic analysis, looking in more detail at the current cold and wintry spell which looks to last well into the first week of February.

 

http://www.netweather.tv/index.cgi?action=news;storyid=6426;sess=

[Nouska]

The one thing the old GFS was good at was picking out a northerly plunge, at long range - likewise its ensembles which we are currently viewing. The fact the ensembles got this and the last cold spell right is no guarantee that they are correctly modelling the future well; especially if there is to be an easterly component to the weather.

 

There is now some firming up on the ensembles with regard to likely pattern. The progressive signals were/are, IMO, a variance of the placement of the 'whoosh' in of the jet stream and the corresponding backwash of cold air. The models are not that good at diffluent/Rex block positioning and this seems to be what is on offer.

 

Pretty good agreement for below average, most of the way, in my neck of the woods - this is a time when looking at ensembles for further afield can be more enlightening than those in the back yard.

 

 

 

Edit to add that Sylvain has provided more parameters for the DWD ICON model - I particularly like the 'temps sensible' option. This is an experimental type of model so accuracy is questionable but it is the first I've seen with a fog and orage forecast on the chart.

 

http://www.meteociel.fr/modeles/icone_cartes.php

 

Edited January 29, 2015 by Nouska

[West is Best]

Oh dear. I was really hoping the slightly improved 0z ensembles would reflect in the 6z, with tightening of the scatter and the others being more in line with the operational. Instead the opposite has occurred, and the control has even gone off on an FI cold outlier.

 

Of course, the op could be right, but to have it this much out from the mean and median of members is not brilliant:

 

 

Until or unless this ensemble situation improves any evolution towards further cold beyond Sunday continues to look a tad precarious to me (I'm putting it as gingerly as I know how).

Edited January 29, 2015 by West is Best

[Jason M]

Interestingly the control run goes for an easterly. At 180 hours the GEFS have support as well albeit the later range GEFS are not particularly inspiring.  

 

As with the 00z suite and the GEM ensembles, it would not be reasonable to say there is a strong signal, but I think there is enough today to say its not an outlier solution and should therefore be treated seriously (along with less palatable options).

 

It seems that there is real confusion over the handling of the PV to our NW and if the longer range models are overplaying this (which is quite likely in my own view) then a real flip in the longer term ensemble suites could occur. The PV doesn't have to move completely from Greenland / Canada as its perfectly possible to get a good easterly with low heights in these locations. Just a slight reduction in its modelled influence may be sufficient.

 

As always, the weather will do what it wants, but in terms of any change to zonality the signal for this is much weaker than just after Christmas. I think the ensemble suites are currently of some use up to say day 8, but after that the uncertainty is just too high.

 

Meanwhile lets hope we all see some snow over the next few days  .

Edited January 29, 2015 by Jason M

[West is Best]

i dont get it....

im uncertain why the tv people are downplaying snow chances for most of the uk when we have charts like this

 

brack2a.gif

 

surely theres huge potential there for alot of people to get snow, but the tv bbc forecasters are only talking about coastal areas exposed to the northerlies as getting any?...

 

Poor upper air temps Rob, that's why.

[Tamara]

So, stratospherically there is now good support for pronounced euro trough allied to vortex displacement. We then also have vortex action of +EAMT and another +EAMT likely sometime in the early part of February

 

At face value the models don't suggest any upper ridge holding over the Atlantic sector, but there are increasing signals that the atmospheric pattern wants to attempt the sort of break-out that often blends itself towards a colder later part of a weak El Nino winter. A second GWO Phase 4/5 orbit following up the recent one is a good clue in this respect.

 

So, I am also suspicious about the lifespan of any far flung ensemble suggestion of returning further westerly mobility to follow early February amplification. Actually more suspicious than I was of the suggestions the other day of the impending return to less cold westerly mobility which, as suspected, is looking shorter than assumed

 

Stratospheric and better atmospheric lead -assistance should be accentuated the longer that time goes on by the natural processes of late winter seasonal wave lengths shortening - and this teleconnects further favourably to increased MJO amplification assistance.

 

I'm reasonably anticipating the Atlantic to increasingly be disposed to increasingly further meridional patterns through February and lead on to more definitive upper blocking

 

Posted by Tamara on 21 January 2015 - 13:41  in Forecasting Model Discussion

------------------------------------------------------------

 

I have posted this again simply as a measure of where we stood a week back,  what the thinking was at the time, and where we stand today

 

Plenty of good analysis continuing this morning about the snow potential for the coming days. Irrespective of any regional IMBY prospects, how good it is to see various parts of the country poised for the first significant snowfalls this winter - and that certainly includes,for example, exposed SW parts such as Cornwall who so often miss out on snow completely. This type of aligned NNW polar airstream, sustained for the length of time it looks set to be, provides lovely prospects for places like these.

 

Some of the rest of us away from coasts and hills exposed to the NW and N await with interest the unreliability of troughs in the arctic airstream which no doubt will produce unexpected nice surprises.

 

With cold weather and snow potential already here to stay for a while anyway - the medium/longer term trends keep continuing to favour us.

 

As posted last night, the Atlantic profile is changing quite radically from the flat pattern of the first half of the winter. The suspicions expressed in the highlighted post last week are proving to have good grounds.

 

In focus to to our part of the NH, this means that the Azores High is declining in (relative) strength as part of upstream changes with decelerated jet velocity and cueing up of repeated amplifications - as often stated of late.

 

Decline of easterly trade winds (with westerly additions to the atmosphere in the sub tropics scrubbing these out instead) weakens the warm Ferrel cell signal that has dominated our winter so far - whilst at the same time (and in compensation) poleward AAM transport of net easterlies to the high latitudes slows the upstream pattern down - and provides background to the trend we want to see for a more sustained colder pattern. 

 

Increase in negative torques (easterly momentum) at high latitudes is supportive for the migration of Atlantic ridging further northwards, as advertised in current modelling, and could just be the first indicator of a change to a more -NAO phase later in the month as energy undercuts in the Atlantic courtesy of split jet flow upstream

 

This is especially the case with the displaced vortex having strong support to hold throughout the next ten days which assists reduction of energy vorticity transport to our NW via the northern branch of the jet stream,our side of the pole. Slower moving clippers/ inland runners across the pond imply more WAA towards Greenland and underpin the sustaining of amplification of our Atlantic ridge.

 

Further GWO phase orbit induced Pacific pattern retrogression beyond the 10 day period suggests consequential renewed downstream amplification and sets the scene for sustained blocking in the Atlantic sector. Meanwhile, feedbacks across Siberia are springing to life and that carved opening across the polar field suggested by the ECM has credible implications in the context of the opportunities that sustained amplification signals through the 10 to 15 day period might offer us, along with the reduced upstream jet flow at higher latitudes in tandem with a displaced vortex.

 

It is on the basis of that little lot going on, that one wouldn't want to place too many bets on exact synoptic developments beyond the most reliable advancement and daily extensions in life-span we are getting to this arctic northerly.

 

We might consider that whilst at the moment the GEM appears the coldest outsider, it is conceivably just simply progressive and rather overstating current trends. It is not without support though at all from these background signals as described. Especially with possible MJO progression in mind. Latest GFS has given a little nod in this direction, and at the very least it underpins the growing trend for the Atlantic to shut up shop and remain susceptible to repeated amplifications.

 

In this respect, GWO fast track orbit back to phases 1/2 (around or just after day 10) corresponds/teleconnects very nicely in February to a very amplified Atlantic ridge and troughing sinking SE into Europe. Again, this would be ideal with amplified MJO progression signals if they evolve to Phase 8

 

Put together, there are good enough grounds for a signal for ridging to evolve across the NE Atlantic, across the top of euro troughing, towards Iceland and Scandinavia... before further retrogression from upstream pulls it westwards once more. And/or an arctic/Siberian High might yet also have some say...

 

NWP seems to me to be picking up nicely on the first of these signals. Just what latitude will this Atlantic blocking achieve ...and what might it eventually morph into?...

 

[Iceaxecrampon]

Same sort of chart as Tuesday with large central belt getting nothing.

 

The Classic Wishbone effect.

 

Ian

[weather eater]

Oh dear. I was really hoping the slightly improved 0z ensembles would reflect in the 6z, with tightening of the scatter and the others being more in line with the operational. Instead the opposite has occurred, and the control has even gone off on an FI cold outlier.

 

Of course, the op could be right, but to have it this much out from the mean and median of members is not brilliant:

 

Screen Shot 2015-01-29 at 12.30.09.png

 

Until or unless this ensemble situation improves any evolution towards further cold beyond Sunday continues to look a tad precarious to me (I'm putting it as gingerly as I know how).

And all of that should be pointing you at the fact that the ensembles are producing no more of a guide than the operationals, its one thing today, something else yesterday and tomorrow. Obviously all of this stuff is here to discuss and it's good to do so but I don't think there is much of an overwhelming case as yet for a long term continuation of the cold or a quicker return to something less so. And even if there was then any of us who have been doing this stuff for years know that  trends have a habit of changing tack. My own view on the ensembles suites and I've said so for years, is that much of the time they makes things more confused and not less so.

Edited January 29, 2015 by weather eater

[Catacol]

Oh dear. I was really hoping the slightly improved 0z ensembles would reflect in the 6z, with tightening of the scatter and the others being more in line with the operational. Instead the opposite has occurred, and the control has even gone off on an FI cold outlier.

 

Of course, the op could be right, but to have it this much out from the mean and median of members is not brilliant:

 

Screen Shot 2015-01-29 at 12.30.09.png

 

Until or unless this ensemble situation improves any evolution towards further cold beyond Sunday continues to look a tad precarious to me (I'm putting it as gingerly as I know how).

 

Surely the fact that the op is now the new GFS model, and the ensembles are running on the old GFS makes it more and more likely that such a split will occur? We all know the old GFS had a progressive bias. We dont have the number of runs we need to be able to compare with new GFS yet - cos its literally too new to tell - but for my part I'm quite encouraged that the op keeps going off on a different solution to the ensembles. It suggests to me that old GFS is doing its usual trick of collapsing the high too quickly - and that in fact it may stick around longer with the chance of an undercut perhaps. 

 

But precarious? Of course. How often is the weather over the UK NOT precarious for cold. About once every few years... and usually when we get a major block to the NE it means dry weather for the majority anyway bar the East coast. There's nothing wrong with precarious.

 

Unless it translates to cold rain all the time. And that's the SW of England today. |-[ I need to move house.

[AWD]

Worth noting the 0z EC ens don't really show great confidence of any sort of warm up or dry up for the foreseeable really;

Bear in mind they are for London too.

[phil nw.]

Just looking at the trend in the ens.graphs we can see the cold spell has extended -the graphs on the left are the older ones.

 

 

 

as the Arctic northerly fades midweek we are left in cold air as pressure rises across the UK so although the trend in the 850 temperatures are slightly up the surface will remain quite cold as we go into next week end.

The odds of the Atlantic breaking through now look much slimmer with some form of blocking likely to develop around nw Europe  by the end of the week.

The day 10 mean height anomalies pretty solid on this.

 

+ve height anomalies stretching ne from the Atlantic to Scandinavia.

 

it's noticeable we keep a cold pool over continental Europe and this could well come this way if the Scandinavian heights become the dominant feature later setting up a cold Easterly.

 

Plenty of interest continues for cold seekers well into February that's for sure.

 

[bluearmy]

the only extended ens that are showing the atlantic headed into a euro trough (disrupting across the uk) post day 10 is the candian. i did hear joe B saying that a recent topic of conversation amongst the pros over there was the good guidance of the canadian ens in the 10/15 day period over the past week or two. just saying ..............

[Hodgheg]

Well at least the models are keeping the cold for longer, lets hope this eventually turns into an easterly. 

[Paul]

Right, that's the polar low thread all setup over here:

 

https://forum.netweather.tv/topic/82413-tracking-the-potential-polar-low-thursday-into-friday/

 

Should be a fun one to keep an eye on!

[Mucka]

Right, that's the polar low thread all setup over here:

 

https://forum.netweather.tv/topic/82413-tracking-the-potential-polar-low-thursday-into-friday/

 

Should be a fun one to keep an eye on!

 

Polar low! (like buses)

 

[Yorlum11]

Is this a second low coming in from Iceland on this run?

 

http://images.meteociel.fr/im/2793/gfs-0-102_rud2.png

 

Mucka beat me to it!

Edited January 29, 2015 by Yorlum11