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Model Output Discussion - The final stretch to Christmas


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Hmmmm...just got a feeling that we should enjoy the pre-Xmas cold snap/spell even if it means only frost and ice as what is on the horizon after that looks again to be once again a bit more Atlantic oriented.

 

Anyway it's only the weather...Happy Xmas everybody! :smiliz34:

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Mean while in the real world away from the MOD... A tragic accident has cost 6 lives in Glasgow. yes this is off topic but a timely reminder of just how unimportant the weather really is in our lives.

There is an enormous lack of respect for other people in this thread at the moment. I suggest that if one doesn't have something to add to the model discussion with a salient chart or pertinent inf

Model uncertainty throwing both operational and ensemble data into discontinuity has proved as rife as was expected a week ago - when AAM flipped to negative tendency along with GWO phasing that was i

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I think worrying about where the PV is setting up and the upstream pattern at this stage is a case of the tail wagging the dog.

The upstream pattern can be exactly the same but it will behave very differently according to the downstream pattern it encounters.

If there is a block well oriented when the jet powers up it will buckle and/or split, if there is a poorly aligned block at a lower latitude it will likely power over the top.

 

Of course what happens upstream is important but the track and speed of the diving low in Europe can make a huge difference to how healthy any block is before the Atlantic tries to push through.

It is a complicated issue because the earlier upstream pattern will dictate how amplified the pattern is as the low dives South and how much pressure will be put on the toppling ridge but if that ridge links up earlier and further West with heights to the East then in general the stronger and better oriented any block will be and the more likely any undercut from whatever the upstream pattern throws at us.

 

Whether we are analysing ECM, GFS, GEM or JMA it is clear that we should be looking East for the main drivers of the pattern if we want a cold blocked setup as explained previously. 

So yes upstream is always important but the conditions that upstream flow will meet will be dictated by the downstream synoptic.

Look out of for an earlier link up of heights (around day 6, the earlier/further NW the better) in future output for a better upstream prognosis.

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Nick the Canadians Chinese and Japanese seem to have spy planes up there hence correct colder solutions showing...unlike the USA an UK an European models who have grounded for a wee scotch over Xmas

Well the Chinese and Japanese I didn't think were into Christmas in a big way so their planes are more likely to be in the air and the GEM is a rubbish model regardless of what it shows. There sorted! lol

 

In terms of the "myth" well I have my I Saw The NWP Drop The Cold Solution And Then Suddenly Bring It Back" T-shirt, I was here as were quite a few of the long standing crew, we saw it happen! but of course until we see hard evidence then it will remain just a myth.

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All to do with upcoming low from the (west - UKO and north west - ECM) and how rapidly it deepens.. GFS - still north.

If it doesn't deepen it stays south and gives more people snow in the short-term, but loses the cold signal quite quickly.

Or deepens more rapidly and pumps up the heights to the west of us, little snow, but gives us a good prospect of long-term cold.

So it seems as if we can have one but not both. Sods law.

However there must be an intermediate way which gives us both?

Can we find it-----

MIA

MIA

The thing that perplexes me is how the models have taken the strength out of that low. The one constant with all the models was the strength to the low. Now it is a damp squib and seems to coincide with the downgrade in the continental feed. I fear that time is too short now to turn this around, the downgrade of that low really did come at the last minute. Edited by blizzard81
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With such uncertainty over the past few days anything past the turn of the Month is still under scrutiny, And with upcoming Stratt warmings and the skitty modeling of the sinking Low on the 27/28th who knows from that point onwards.. About as complicated and as interesting/exciting as Model watching gets.  Merry Christmas  :smiliz19:

Edited by Polar Maritime
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Hi, been following this thread for a month or so now and this is my first post. I am a keen weather enthusiast and really like snow days in winter and thunder storms in summer... thought i had a good understanding of the weather and factors which change our weather here so much from day to day.

 

however since reading these posts i understand there is alot more going on that no matter how much computer power these models have they will never be able to predict the weather too far in advance which will always make it interesting for us weather folk :)

 

I live in the North East and are hoping for snow this boxing day night/saturday, also a much more prolonged cold spell which we are well overdue.

 

Anyways, keep up the good work and insight and merry christmas

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Just to say again I would also I would like to thank everyone on here for the there weather knowledge, reports and banter throughout the year and wish you all a very Happy Christmas and a wonderful New Year    :)  now bring on the snow please    :)   :)

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The thing that perplexes me is how the models have taken the strength out of that low. The one constant with all the models was the strength to the low. Now it is a damp squib and seems to coincide with the downgrade in the continental feed. I fear that time is too short now to turn this around, the downgrade of that low really did come at the last minute.

 

It is  because a weak low will not pump up the high to the west as far north, and hence the easterly cannot formed. We must have the heights above the level of Northern Ireland to succeed with an easterly.

 

MIA.

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Hi, been following this thread for a month or so now and this is my first post. I am a keen weather enthusiast and really like snow days in winter and thunder storms in summer... thought i had a good understanding of the weather and factors which change our weather here so much from day to day.

 

however since reading these posts i understand there is alot more going on that no matter how much computer power these models have they will never be able to predict the weather too far in advance which will always make it interesting for us weather folk :)

 

I live in the North East and are hoping for snow this boxing day night/saturday, also a much more prolonged cold spell which we are well overdue.

 

Anyways, keep up the good work and insight and merry christmas

 

Welcome doc32. Do we really have 31 other drs?

 

Seems like the extreme weather forecast for your patch is less likely now, but you may get a snowfall, if it comes that far north.

 

MIA

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I think worrying about where the PV is setting up and the upstream pattern at this stage is a case of the tail wagging the dog.

The upstream pattern can be exactly the same but it will behave very differently according to the downstream pattern it encounters.

If there is a block well oriented when the jet powers up it will buckle and/or split, if there is a poorly aligned block at a lower latitude it will likely power over the top.

 

 

 

Yes I agree it is complicated. But it is all about probabilities. If we have an upstream NE Canadian/Greenland raging PV lobe then there is less chance IMO of a favourable cold flow. Of course if everything downstream is perfect then it might not matter, however that is rarely the case; an undercutting Atlantic is a nightmare to verify. So the D5-8 signal of a PV building in NE Canada is not a positive development and clearly negates the chances of a cold pattern in our sector in that time period. 

 

The GEFS over the last few runs have tried to build a cold picture from a promising D5 but run after run they fail and flatten the pattern, a sure sign that the signal is not strong enough to succeed re a HLB. The D10 mean:

 

post-14819-0-01681300-1419450101_thumb.p

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It is  because a weak low will not pump up the high to the west as far north, and hence the easterly cannot formed. We must have the heights above the level of Northern Ireland to succeed with an easterly.

 

MIA.

 

But what a more shallow low does is keep the cold air that does come in during xmas more or less over us and not get mixed out by milder air and tonights ECM is a good example of the former... The problem we may have is just the lack of PPN and the lack of timing before pressure rises too much. 

 

Sadly the models don't seem to indicate much in the way of convective weather but the Fax charts will be interesting too see if there is any troughs mixed in with the flow. 

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This forum has a mix of excellence and schizophrenics  :wallbash:

 

 

This morning some were euphorically trumpeting an easterly and explaining how it was really all so predictable based on Alaskan ridging, shortwaves off Philadelphia, and a shattered PV.

 

This evening some (often the same people) are in a state of gloom due to a return of a zonal flow, and explaining how it was really all so predictable based on Alaskan troughing, shortwaves off Greenland, and a strong PV

 

 

As a casual reader I'm just giving my opinion on a thread which generally seems long on over-reactions and short on rational consideration ........... and again I stress that there are some excellent posts in amongst it all.

I understand where you are coming from but that is part n parcel of being on this forum and makes it what it is.
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What drama still tonight, makes for an interesting Christmas Eve though! So 48 hours out and still realy no agreement. Perhaps a shallower low now?

 

Im a little disapointed with the ECM tonight, the latter frames dont make a lot of sense to me (although im no expert!) it sort of dances around a bit. From what I can see though, the Atlantic gets close, but doesnt get past the UK and towards the end the high is ridging North again, so perhaps not so bad. It shows it has some strength in it, and as we saw in November, the models are always quick to remove a high and its never that easy. If we do get the cold air in as predicted then thats always hard to shift aswell :)

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Yes I agree it is complicated. But it is all about probabilities. If we have an upstream NE Canadian/Greenland raging PV lobe then there is less chance IMO of a favourable cold flow. Of course if everything downstream is perfect then it might not matter, however that is rarely the case; an undercutting Atlantic is a nightmare to verify. So the D5-8 signal of a PV building in NE Canada is not a positive development and clearly negates the chances of a cold pattern in our sector in that time period. 

 

The GEFS over the last few runs have tried to build a cold picture from a promising D5 but run after run they fail and flatten the pattern, a sure sign that the signal is not strong enough to succeed re a HLB. The D10 mean:

 

attachicon.gifgens-21-1-240 (1).png

Hi IDO,

 

 

I do agree and understand what you are saying but the set up and orientation of the high comes before the reorganisation of the PV lobe to the NW. If that high is allowed to sink SE then it will be all but impossible to get any undercut regardless.

Therefore IMO there are good reasons for concentrating on events downstream, re the diving low and any link up of heights to the NW, as they happen prior to further upstream shennanigans.

I'm not saying we shouldn't look at how the jet is aligning during this period of the output and the possible upstream ramifications, just that these cannot be known until the position and orientation of blocking high are better known. 

Also the immediate upstream is also important re amplification and how much pressure is put on the ridge.

 

I think this race between upstream and downstream pattern dictating the flow over the UK is a microcosm of the larger battle between air-masses, cold East and warm West.

 

Steve M alluded to shortwaves embedded in an East flow earlier but that can only happen if we have the link up of heights and keep the trough pinned in over Northern Europe so that there is a reversal of flow and low pressure begins to come back West rolling under the ridge.

This is a classic Easterly set up because it keeps the high at a higher latitude, enhances the East flow also at a higher latitude and presents a formidable block for the oncoming Atlantic to overcome.

 

I think we are essentially on the same page but later upstream pattern is less important than earlier downstream one IMO, hence the tail wagging the dog comment although I do understand how this can be seen as one of those what comes first scenarios. Does the jet dictate to the blocking pattern or does the blocking pattern dictate the jet profile?

For me it is the latter in this instance and if we don't get a good link up of heights to our NE quite early I expect the jet to override the block later regardless of upstream variations unless we get very southerly jet not currently being modelled except where the jet is forced by the block later. ie JMA

 

There is no real right and wrong, just a difference between what weight we are giving the various parameters.

 

Fingers crossed we get both a good block in place and an advantageous upstream flow. :good:  

Edited by Mucka
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With the upcoming low pressure programmed further and further south with every run as we get closer to T+0 this is where I suspect the low pressure will end up being come Friday/Saturday.

attachicon.gifBoxing Day27th.jpg

Trans-Pennine routes, the Welsh Mountains and SW/Dartmoor I suspect will get some disruptive snowfall with drifting as the low exists SE.

With the NW/N/NE winds subjected to increase rapidly across EA and Kent as the low exits SE into the Continent I wouldn't be surprised to see inland gusts in excess of 65 mph with 70 mph along the Lincs/EA coastline. With SST's still relatively high I think any chance of snowfall will be minimal across Norfolk, Suffolk and Essex. Head into Cambridgeshire and Hertfordshire, and your chances of snow increase somewhat.

It's nice to see the risk of snow across England after what was a very mild, wet and windy Winter 2013/14.

Merry Christmas all.

Mammatus :-)

Pretty much in line with the ECM

f4h8hf.jpg

Highest risk around southern uplands in northern England.

Edited by Cheese Rice
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Good Evening, and a Very Merry Christmas to everyone :smiliz19:  Well at the least the models have predicted the Christmas weather being rather cold days ago, and seeing as that is the weather we will be having, Merry Christmas to the ecm and gfs as well :smiliz34:  The stormy low which was a big feature  some days ago has been squashed now to a much lesser concern, but perhaps this feature although not such a wind maker, will make headlines for other reasons. Out further ,both ecm and gfs  "try" to bring the Atlantic in, but both models show quite a stand-off between the Continent and the Atlantic, so Zonal  NO, but we are stuck in the middle with regards to the Uk at T+240  Of course the pendulum could swing either way, but as we are entering deep winter, any block to the east or northeast of us throws us a chance of a very cold spell,,,,,,,, :w00t:

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Not sure why some are surprised by the ecm 12z. Imo, any solution post day 5 is as valid as any other. Upstream/downstream/high up/ - so many variables and very little guidance as to what has the upper hand. The only consistent signs I have seen across the modelling is the strong push of the jet into the n Atlantic in about 8 days time and a propensity for ridging to be in the nw Europe area. That leaves a lot of gaps to be filled in.

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Hopefully ian fergie can shed a bit more light on this weekends low!! Am not really looking to far ahead when we got some excitement snowise in less 60 hours!! But that low keeps pushing south steadily!! My thinking is it will eventually run directly though the midlands!

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