Model Output Discussion 23/11/2012 18Z onwards

[TEITS]

Think of this one as a slow burner, and remember many great winters only had teasers at this stage, including the legendary winters...

Spot on mate.

Lets use Dec 1978 as an example because despite the blocking it took a full 10 days before the cold air finally arrived.

http://www.wetterzentrale.de/archive/ra/1978/Rrea00119781221.gif

My main focus is that blocking is continuing to be modelled right out to +384.

[ukpaul]

Both the OP and Control actually at the colder end of the short ensembles.

[The Eagle]

My take is that the 18z is a certain downgrade though it's still cold and not bad but the narrative is changing to a more northerly route rather than east or even northeasterly and with that the longevity of the cold spell is shortening. Hopefully the UKMO/GEM is route is what we see in the morning but I have have my doubts as ECM/GFS are quite similar now up to 168hrs and the ensembles are also turning against us a little. No need for panic but a certain shift today in the overall forecast.

Edited November 23, 2012 by The Eagle

[nick sussex]

For what it's worth the 18z NOGAPS looks nice at +144, looks less keen to move the low over Europe too far north than GFS/ECM. A Beast from East would follow on I think.

Yes thats closer to the UKMO output but with the GFS and ECM both going for a similar pattern you'd have to put that as a more likely outcome.

Once the Arctic high starts slipping se into Russia theres no forcing on the European trough.

So you end up with two high pressure cells separated by the trough. As I mentioned earlier theres more margin for error with this further s and e, even if you get a pull north on the eastern side of the trough you're more likely to keep a more northerly flow as this happens.

Hopefully we'll see some agreement tomorrow given that events are now within 144hrs.

[Cheshire Freeze]

Both the OP and Control actually at the colder end of the short ensembles.

Yes the ensembles are decidely dicey at 192....have been through them all one by one and in general blocking is a lot weaker as a common theme.

[Downburst]

Is it still only November?It seems like we have been following this build up to the long heralded -AO/-NAO changeover for an age Nick.

In spite of the operational runs variations at quite short range we can take a lot of positives-if looking for cold- from the mean Ht 500hPa anomls in the ensembles and naef`s outputs and of course from the Stratosphere.forecasts.

Looking over the ECM and 18z GFS once more and keeping in mind the anomaly charts for December I think perhaps we are all getting caught up in the detail and perhaps expecting arctic conditions to start and run Dec 1 to ...well end Feb. Anomaly charts are only showing deviation from the average. I have yet to see an chart that takes that and give exact forecasts for local conditions. The anomaly charts are very neat and we then expect the end result weather to fit the neat pattern. I do expect a blocked and cold December. At the very least similar to Jan /Feb 2010 but with some December 2010 mixed in.

When is GP's forecast coming out? I am getting impatient...

He showed a composite for January today. If December pans out with the cross polar flow he predicts you can expect to wish for spring by end of January.

[swfc]

Regarding the low pressure to the south east.Why does it not slip south east and allow an easterly to develop?I can see the high to the south east but normally with pressure in the north you would expect it to move south east towards the med????

[bobbydog]

When is GP's forecast coming out? I am getting impatient...

probably when he has a clue whats going to happen, same as everyone else! he forecasts the weather, he doesn't control it lol!

[kold weather]

Yes the ensembles are decidely dicey at 192....have been through them all one by one and in general blocking is a lot weaker as a common theme.

Hard to take them seriously when they continue to implode the northern blocking as fast as they are, especially as many are pulling some rather odd looking evolutions between 168-240hrs.

Expect everyting to end up a solid 200-300 miles further south then what the models are expecting at the moment. That tends to be what normally happens.

[weirpig]

Looking at the projected rainfall totals for this coming weekend do any of you think that the totals are slightly exagerated, some areas are expecting over 100mm of rain, that seems a big jump from the 12z.

[Cheshire Freeze]

Sorry to say but the FI ensemble mean isn't pretty, a lot flatter than the 12z suite and suggestive of a mean westerly flow.

[pyrotech]

it is correct

a small area of 528 just ahead of the trough they have marked with the main 528 line further north-nothing wrong with it assuming the idea of the trough and a patch of colder air is correct.

Thanks John, first time i have noticed it on them like that, glad to have someone like you on here from the industry to guide us

[Liam J]

Sorry to say but the FI ensemble mean isn't pretty, a lot flatter than the 12z suite and suggestive of a mean westerly flow.

Cheer up, it's nearly Christmas

[January Snowstorm]

My take is that the 18z is a certain downgrade though it's still cold and not bad but the narrative is changing to a more northerly route rather than east or even northeasterly and with that the longevity of the cold spell is shortening. Hopefully the UKMO/GEM is route is what we see in the morning but I have have my doubts as ECM/GFS are quite similar now up to 168hrs and the ensembles are also turning against us a little. No need for panic but a certain shift today in the overall forecast.

Couldn't agree more.

No need for panic but as you say a shift has taken place to a more Northerly shorter attack

The whole synoptics are on a knifedge and could go either way at around 120hrs

On a positve note contined signs of blocking over on the strat thread

[ukpaul]

Sorry to say but the FI ensemble mean isn't pretty, a lot flatter than the 12z suite and suggestive of a mean westerly flow.

No suggestions of a reformed PV though bar one or two perturbations. This may be a weak first attempt with some cold but little snow but the underlying synoptics are going to lead to more attempts and one or more will succeed.

[BLAST FROM THE PAST]

What a chart this is, especially if one looks at the build up....prolonged cold pattern digging in. My chart of the day and one I want to come to fruition

Lets see what weekend and early next week brings.....see if there are any chinks in the armour. We don't IMO want to see an attempt to go down the northerly route...it could be an issue.

BFTP

Edited November 23, 2012 by BLAST FROM THE PAST

[Weathizard]

Sorry to say but the FI ensemble mean isn't pretty, a lot flatter than the 12z suite and suggestive of a mean westerly flow.

Agreed the ensembles aren't pretty but the GFS seems to swing a lot at the moment, its a load of variations and to be honest I'm sure you'll agree some of the ensemble members are downright bizzare, they destroy the ridging thats holding off the atlantic at what seems a blink of an eye, and for that reason I won't ignore them, but I will put them to one side for the moment, ah well its all part of the roller coaster that the GFS ALWAYS provides.

Trust the GFS though to be the one that brings the Atlantic back in, it seems as though it has a certain bias, is this the case do you think? Because in my inexperienced mind, I just cannot see the Atlantic coming back in for a long time, all background signals suggest otherwise?

Edited November 23, 2012 by Weathizard

[pyrotech]

Looking at the projected rainfall totals for this coming weekend do any of you think that the totals are slightly exagerated, some areas are expecting over 100mm of rain, that seems a big jump from the 12z.

Rainfall totals are high there as the cold front is likely to be becoming occluded around that area, plus then as the low moves North and east you get the wrap around occlusion dragging thru. The cold front will give heavy rain but where it catches up with the warm front it could become very heavy. Then obviously the time it takes for wrap around occluded fronts to move thru. The "fax charts" show this quite nicely.

However position could change if system does not travel thru as expected.

Actual amounts of percipitation can change alot too, different models have different solutions.

[nick sussex]

As much as I might seem to be too overly critical of some of tonights outputs the signals for cold are still strong.

I'd go as far as to say if we can get a favourable outcome within 144hrs in terms of location of troughing then its looking very good for an extended spell of cold and chances for snow.

We just need a little bit of luck here regarding that shortwave to the west and that the troughing sees a correction further south and east.

If I see that tomorrow then expect an altogether less grumpy and almost ramp like series of posts!

[swfc]

Regarding the low pressure to the south east.Why does it not slip south east and allow an easterly to develop?I can see the high to the south east but normally with pressure in the north you would expect it to move south east towards the med????

Take it know one knows then?

[Bristawl Si]

Sorry to say but the FI ensemble mean isn't pretty, a lot flatter than the 12z suite and suggestive of a mean westerly flow.

Sorry to say but the FI ensemble mean isn't pretty, a lot flatter than the 12z suite and suggestive of a mean westerly flow.

Pathetic really.

One Run - Cmon CC u know better than that!

[Staffordshire]

Looking at the projected rainfall totals for this coming weekend do any of you think that the totals are slightly exagerated, some areas are expecting over 100mm of rain, that seems a big jump from the 12z.

never post here, but yes i was thinking this, any answers?

[Bobby]

I just cannot see the Atlantic coming back in for a long time, all background signals suggest otherwise?

The NAEFS anomaly maps show the blocking fading and transferring NW allowing low pressure gain control from around +240, by +300 the Atlantic looks well in charge. The jet stream is quite south so probably not mild.

Cold, messy and wet might what we end up with eventually I fear. The GEFS ensembles show a similar thing.

NAEFS pressure/upper temperatures at +300

We'll see

Edited November 24, 2012 by Barb-

[Weathizard]

The NAEFS anomaly maps show the blocking fading and transferring NW allowing low pressure gain control from around +240, by +300 the Atlantic looks well in charge. The jet stream is quite south so probably not mild.

Cold, messy and wet might what we end up with eventually I fear. The GEFS ensembles show a similar thing.

NAEFS pressure/upper temperatures at +300

Pl

IF that is the case then why are 95% of other posters and the stratospheric lot, saying that this blocking will be hard to budge? This question is open to everyone by the way, just a little confused at the moment with regards to where we stand blocking wise? Obviously we have great sypnotics, a completely destroyed vortex but we don't have the real pool of cold uppers but if this first shot fails, which it probably will, where do we go from there?

+ Does the GFS in particular have a tendency to power up the Atlantic? I personally think it does.

Edited November 24, 2012 by Weathizard

[Panayiotis]

The NAEFS anomaly maps show the blocking fading and transferring NW allowing low pressure gain control from around +240, by +300 the Atlantic looks well in charge. The jet stream is quite south so probably not mild.

Cold, messy and wet might what we end up with eventually I fear. The GEFS ensembles show a similar thing.

NAEFS pressure/upper temperatures at +300

They are not as bad as you think, for example the pressure is quite high over Southern Greenland and all of the BI is covered in sub zero upper temps.