Model output discussion - heading into 2018

[Man With Beard]

Two spells of snow on the ECM 00Z: first a rain/snow mix for the South on 26/27th, and then for the Midlands/ North West on the 29th - after which is goes mild by New Year's Eve. 

[MR EXTREMES]

ECM slowly builds height into Russia with vortex being pushed towards Greenland.

Unsettled wet windy cold in the north at times.

Still nothing to be enthusiastic about here in the south.

Might take something special to remove this current pattern.

But anyway wishing everyone a very merry Christmas on the best weather forum on earth.

And good health to all.

[knocker]

Pretty much as covered by the recent anomalies. Rather not comment further until the EPS is out

 

Edited December 24, 2017 by knocker

[tight isobar]

15 hours ago, tight isobar said:

Gfs 12z has shunted slider LP further south...

And we know the gfs is a little wobbly with precip rates/types..

However if its anywhere near on the money' there is some very notable falling snow rates as the system heads east into the north sea...

And east midlands right down across home counties and across east anglia through to kent may get a dumping...

Again all speculative atm but coming into better range now.

Still opting' for a similar outcome this morning.

However a slightly different dynamic is that i feel the upper air temps are-and will be modeled a tad cooler nearer to the time.

There is a slight catch up of colder air digging in behind/under the system' with a quicker transitonary period from rain-to snow.

South east midlands down and around m4 corridoor-through into kent essex...

Highly likely slushy accumulations(away from elevation)..

But as-again nowcasting will be crucial.

And the 850 values are imo being undercooked atm.

Some more fun and games looking v-likely, and no doubt some may be suprised-while others are wondering why there is such a thing as marginality!!!!

Edit: to add- some intresting ozz ens.

London.00z ens

Edited December 24, 2017 by tight isobar

[Chesil View]

A very happy xmas to all my fellow weather enthusiasts. ( yes even the mildies). Good luck to those with a chance of snow over the next few days. I,m taking a model thread break for a few days hopefully by which time the we will get an inkling of what will follow the milder weather due around new year. Enjoy your festivities everyone.

[stewfox]

1 hour ago, Man With Beard said:

Two spells of snow on the ECM 00Z: first a rain/snow mix for the South on 26/27th, and then for the Midlands/ North West on the 29th - after which is goes mild by New Year's Eve. 

'Flip' is the buzz word this Christmas.  First two in the reliable so snow on the cards. If teleconnections can flip and models, ensembles averages can flip it won't be  flipping mild by new years eve. 

[JBMWeatherForever]

We are all so familiar in the British Isles to seeing our forecast cold spells being downgraded and watered down as the start of such a spell eventually arrives. But what we now have in front of us for once is the complete opposite! Perhaps the weather has taken pity on us and is starting to get into that holiday mood. There may perhaps even yet be some further upgrades to this increasingly good looking cold snap !  

I really hope that everyone has a Very Merry Christmas and a Happy 2018, with lots of exciting weather too ! 

[knocker]

Nothing surprising from the EPS 6-10 anomaly this morning with a rather diffuse vortex with two or three lobes and a strong westerly jet leaving the eastern seaboard portending a continuation of unsettled weather with temps generally around average.

Meanwhile some very cold temps at the end of the week across North America as Arctic air is displaced south.

[mb018538]

It seems to me that whenever a massive bitter cold chunk of the vortex gets sent down the east coast of the USA, this obviously massively increases the thermal gradient into the Atlantic and revs up the jet to brew some monster storms. Everything else seems to just cave in at this point and we end up at square one.

my question is....can you get a decent set up out of this?? As in decent blocking quickly evolving from this scenario? I always get that sinking feeling that zonal is going to be locked in for weeks and weeks when we are now approaching the best part of winter.

[snowking]

Snowfall for Tuesday night into Wednesday still a strong possibility with the overnight runs. ECMWF has been fairly consistent with the track of this over the last 24 hours, though it remains further south than some - the control also gives a fairly similar track (with a little more intensity) and whilst as ever there is huge variance within the ensembles, the track shown below is about the biggest "cluster".

Still a lot of runs to go before we can make a best guess though 

 

[Summer Sun]

UKMO doesn't look quite as unsettled as ECM at t168 as we can see by the position of the low on ECM the south though could have some fairly heavy rain for a time if UKMO is correct

[northwestsnow]

Aprege is a disaster for those wanting snow, some wet snow for a time as the low zips across the home counties, mainly on the northern edge. 

 

 

about as good as it gets.

 

 

 

Its also gone way south along with the others.

Looks like chris fawkes tweet about heavy snow across the pennines was twaddle.

 

Edited December 24, 2017 by northwestsnow

[bluearmy]

17 minutes ago, northwestsnow said:

Aprege is a disaster for those wanting snow, some wet snow for a time as the low zips across the home counties, mainly on the northern edge. 

 

 

about as good as it gets.

 

 

 

Its also gone way south along with the others.

Looks like chris fawkes tweet about heavy snow across the pennines was twaddle.

 

Would have thought he would have learned from the last slider that the ecm was likely the best guidance for placement of the system - anyway, Tuesday nights low  is modelled again to be more round and less flat which leads to a smaller snow area (add the twist ne as it approaches the continent ) and the flow ahead of the occlusion is less continental and more North Sea. Thursday looks more akin to the slider of a couple of weeks ago with several lows sliding se along the next occlusion. That's got a way to go yet. Plenty to watch whilst we aren't working! 

[karyo]

20 minutes ago, mb018538 said:

It seems to me that whenever a massive bitter cold chunk of the vortex gets sent down the east coast of the USA, this obviously massively increases the thermal gradient into the Atlantic and revs up the jet to brew some monster storms. Everything else seems to just cave in at this point and we end up at square one.

my question is....can you get a decent set up out of this?? As in decent blocking quickly evolving from this scenario? I always get that sinking feeling that zonal is going to be locked in for weeks and weeks when we are now approaching the best part of winter.

I suggest you read Catacol's post from last night. It is the best post I've read here in a long while. 

The worst model today for cold is the UKMO. It quickly loses the chilliness and brings a mild southwesterly with the Azores high ridging into Iberia and France. 

The ECM is better as it doesn't get as mild thanks to a more westerly flow. It still has the pressure rise in Iberia though.

[Guest]

LAST ONE FROM ME FOR A FEW DAYS

I thought that I'd sign out on a happier note. Further to my "slider 2 vs slider 1" post yesterday (on page 14) where I attempted to examine just how marginal any lowland rain/snow might be in the south for this Tuesday/Wednesday event, I see that the most recent output looks just that tiny bit more encouraging. I mentioned the temperature profile requirements that @johnholmesoften reminds us of but I could not find the link to the details that are buried somewhere in the NetWeather archives. Well thank you @knocker for providing that (see his post immediately below mine on page 14). The "wet bulb" temperatures are rarely posted anywhere but another big thank you to Karl @frosty for kindly finding them and including these in his post this morning (several pages back). These values are just about low enough but ideally need to drop another degree or so. The last couple of runs shows some slightly lower 850s and these plus the surface temperatures indicated are getting very close to the "critical" levels and we'll only need the smallest of upgrades to get there. The only missing and essential ingredient was the dew point temperatures that really need to be around or, ideally, below zero. The "weatheronline" site does provide dew point charts (but we are not meant to post them on here) and GFS also produce them but on their subscription services (as do NetWeather who use them). I just found them on Aperge (free to view and postable).

Aperge 0z  2m Dew Point Forecasts:

     T+72 for 0100 Dec 27th               T+78 for 0700 Dec 27th               T+84 for 1300 Dec 27th               T+90 for 1900 Dec 27th            T+96 for 0100 Dec 28th   

              

These are actually hourly charts. To view the whole period in greater detail (and for future runs) here's the link: http://www.meteociel.fr/modeles/arpege.php?ech=90&mode=18&map=330

The really good news is that the predicted dew point values for the time of the slider 2 event have also dropped. They still look a fraction too high at the expected beginning of the event but by dawn on Dec 27th, some 0c values are starting to show and some sub zero values begin to crop up as we pass through the day. Overall, all the ducks might just about fall into place for some of us "lowlanders" to see snowfall. If it develops, it'll most likely be on the northern edge of the system and may be confined to quite a narrow band. There may also be some back edge snow as cold air digs in behind the system. "If" the very recent slight trend down in most of these key values continues then the snowfall might be a little more widespread. Of course, how much settles is another matter but any heavier bursts might give a covering and very slight elevations (just 50 to 100 metres) can make an enormous difference in these marginal set ups.

The next few runs might reverse the downward trend in temperatures (as well as change the track of the LP) but for "coldies" and "snowies", I hope that your wishes are granted. So, in conjunction with my post on page 14, the link provided by Knocker, Frosty's wet bulb readings and the Aperge dew point charts above, those of you following this over Christmas can keep an eye on the progress. Once we get to late on Boxing Day, then the excellent "live" dew point and temperature charts are available on the Meteoceil site - they usually automatically update every 10 minutes. Here are the links:

http://www.meteociel.fr/observations-meteo/point-de-rosee.php?region=uk    and  http://www.meteociel.fr/observations-meteo/temperatures.php?region=uk

Enjoy the snow chasing!  Finally, may I wish everyone a very Happy Christmas.

 

Edited December 24, 2017 by Guest
Correct typos and check charts & links

[northwestsnow]

FWIW GFS 6z looks much better for snow across much of England and wales than EC/UKMO

[knocker]

3 hours ago, West is Best said:

I. I've lost count of the number of times we are told that our weather pattern is now set in stone, only to find it all changes a few outputs later.

Happy Christmas everybody  

x

 

Then I suggest you have a serious think about who you listen too as no meteorologist would say that or even people with a genuine interest in meteorology

[shaky]

9 minutes ago, northwestsnow said:

FWIW GFS 6z looks much better for snow across much of England and wales than EC/UKMO

Yeh gfs just as consistent!!justfeel its gona be wrong though with all other models pushing it further south!!

[bluearmy]

4 minutes ago, northwestsnow said:

FWIW GFS 6z looks much better for snow across much of England and wales than EC/UKMO

The problem with gfs is that on the last slider,it never really got the track right until it arrived! So waiting until the Xmas 12z runs for x model agreement may still prove fruitless. With most of the models on the south England track I'll stick with that and if anything, expect a little adjustment south more than north. As I said earlier, some elongation of the trough would assist with snowfall amounts and area covered. 

[Man With Beard]

17 minutes ago, northwestsnow said:

FWIW GFS 6z looks much better for snow across much of England and wales than EC/UKMO

Another ECM Vs GFS battle coming up over the placement! ECM whipped GFS last time - who will be on the money this time.

Must admit I didn't expect anything like this to materialise for next week!! There's always the chance of something popping up when you're in a westerly (not south-westerly) flow - but this really would be a fluke - low pressure getting just east of north to the UK, a small gap between this low and the next one incoming (thanks to the Arctic ridge that wasn't really picked up to its full extent on the ens until about D11), a little cold air getting south as a result, and then a runner low underneath the cold providing precipitation whilst keeping the wind from a north/east direction. Who says we never get lucky for snow in the UK!!

Edited December 24, 2017 by Man With Beard

[tight isobar]

13 minutes ago, northwestsnow said:

FWIW GFS 6z looks much better for snow across much of England and wales than EC/UKMO

Again be careful when taking any gfs-related precip/alignment charts any further than 24 hrs out..very dodgy..

The ecm as previously is looking closer on the money now! Regarding track placings.

But still perhaps a few minor shakes?!

And still plenty to forward to.

I'll likely be to p####d to focus on radar come the time anyhow?..

So what will be-will be.

Merry christmas one and all...

Whatever the weather ?

Edited December 24, 2017 by tight isobar

[tight isobar]

Icon...good performer on last slider.

Has a fare bit of accumulation..south/south east england..

Similar to ec-accum mod...

Lets see ay!!!

[karyo]

1 minute ago, tight isobar said:

Icon...good performer on last slider.

Has a fare bit of accumulation..south/south east england..

Similar to ec-accum mod...

Lets see ay!!!

ICON was persistently too far north with the last slider. It only got it together 12 hours before the event. It was even further north than the gfs.

[Interitus]

11 hours ago, Catacol said:

For those hoping for some cold and seasonal weather heading into January the signals have taken a significant turn for the worse. Negative anomalies in the tropical western pacific forecast to be removed altogether, allowing a big surge in trade winds and removal of AAM from extratropical regions

Loss of AAM at 10 days now sees ensemble data remove pretty much all high lat blocking, with high pressure instead forming a neat belt around most of the hemisphere in mid latitudes.

All of this is then reflected in the excellent GWO tool - for the first time in a good while the spiralling rise in GLAAM has zigged back towards 7.00 on the phase chart... and we are headed now for a period of phase 1-2-3 activity.... low on blocking and high on westerlies in a more "classic" Nina setup.

It has been a sudden and somewhat unexpected turnaround. There was no suggestion of a sudden removal of tropical pacific convection strength: indeed the NOAA report of only a week ago saw a slow and steady movement through 7/8.. and ongoing wave 1 activity via favourably positioned blocks had kept the vortex quiet. So what has changed? A very good question. I scan the web and twitter pretty frequently and have not spotted an explanation yet: only observed reality and a prognosis for the next 15 days brought in line with observed data

Increased zonality in the midlatitudes typically means higher AAM in this region - flatter jet, increased u-wind = higher AAM by definition, a wavy meridional jet has higher v-wind and lower AAM. This can be seen by comparing a chart of AO as a proxy for zonality, with charts of AAM and its tendency, broken down into 6 time periods - the constrast between midlatitude and subtropical AAM reflects the AO -

1. From start of October, positive AO = westerly winds = positive midlatitude AAM constrasting with negative in the subtropics. AAM anomaly and tendency showed a rising trend during this time, but as this is obviously global, it is skewed one way or another by the southern hemisphere as well so is not always representative.

2. Neutral AO, lower midlatitude AAM, less contrast with subtropics.

3. Gradually falling AO associated with northward propagation of -ve AAM tendencies and southwards +ve AAM.

4. Sudden -ve AO alongside sudden -ve AAM north of 60° - high latitude blocking.

5. Another neutral period - subtle variations in midlatitude/subtropical circulation and hence AAM but contrast remains pretty flat.

6. Positive AO again, positive midlatitude AAM, negative subtropical AAM anomalies.

How you relate this to a GWO/GLAAM budget is up to you, but zonal midlatitudes means higher midlatitude AAM.

 

With regards to the MJO, the NOAA CPC outlook from 18th December (http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjoupdate.pdf) was pretty clear that there was doubt whether the MJO would progress and whether it would be of significant strength -

Quote

The active phase of the MJO is currently approaching the Western Hemisphere, but is interfering with the background La Niña state that is suppressing convection near the Date Line.
Models show eastward propagation of the MJO envelope for at least the next week or so, before diverging on whether the signal will weaken or continue across the Western Hemisphere.
Some caution should be taken with the aforementioned model forecasts that show a weak MJO over the Western Hemisphere, as low frequency enhanced convection building over the Maritime Continent in association with La Niña could be biasing the RMM index towards Phases 4/5 and away from Phases 8/1.
Even if the MJO does make it across the Western Hemisphere, any substantive extratropical teleconnections are unlikely until the signal reaches the Indian Ocean.

They go on to add -

Quote

In early to mid-December the MJO crossed the Maritime Continent into the Pacific, and coupled with active equatorial Rossby wave activity, enhanced convection in the West Pacific.

This can be seen in an accompanying 850mb wind plot -

Increased activity around 130°E but east of this increased easterlies from the westward propagating equatorial Rossby wave. Hovmoller charts based on the Wheeler/Weickmann method show the MJO being snuffed out by the wave -

But the model guidance tends to want to continue propagation, here from the CFS -

[tight isobar]

4 minutes ago, karyo said:

ICON was persistently too far north with the last slider. It only got it together 12 hours before the event. It was even further north than the gfs.

As most will(12hrs former)..

But using it in compare to ec output...

Its a worthy shout as things stand.

But we all know minor tweaks have big ramifications.

And i can see it now.. the green eyed monster rearing its head in here, as some fail again on the coming situation.

Edited December 24, 2017 by tight isobar