Model Output Discussion: 12Z (22/11/12) And On...

[Cheshire Freeze]

Last one from me on the 12z model runs; feel like my points are rather laboured today.

We can only comment on the output before us and in the last 24 hours (since the 12z runs yesterday) there has been a TREND by the operational model outputs away from any real cold advecting across the UK. We also now appear to have another shortwave palava on our hands; and this is exactly the reason I urged caution yesterday.

Long term we may see proper cold (low upper air temps & thicknesses) infiltrate the UK but within the next 8-10 days I think it's going to be a real struggle.

[Liam J]

That JMA run looks awful for wanting to keep the blocking by the looks of it!

The charts do demonstrate why I prefer Northerlies at this time of year, much more reliable in terms of getting cold uppers heading southwards and the best easterlies do tend to occur deep into the winter months rather than late Autumn.

Really? Quite the opposite imo.... Greenland, Arctic, Scandi - look at the heights.

Edited November 22, 2012 by Liam J

[nick sussex]

Regardless of the modelling disagreements it is going to turn colder.

And that really is the sum total that can be drawn from the output! Trying to forecast any snow at this point is impossible as we have no idea where exactly that European troughing will set up, whether shortwaves near Scandi will hinder any cold, whether the Arctic high runs up against the UKMO and its shortwave love-in!

I'd draw a line under this evenings output and hope to see a model convergence tomorrow,

[Isolated Frost]

D7 composites- GFS composite closest, ECM just ahead of JMA composite- it'll be interesting to see how the H5 anomalies shape up throughout the next few days and they will be vital in terms of model verification- the short-scale bits will be determined in time

[Severe Siberian icy blast]

No you'd need sub -7c or lower in an easterly to see some decent snowfall, closer to -10c if you want some juicy snow making convection with a strong air flow. An Atlantic front could bump into T850's of 0c or just below and produce mega falls a la February 1996, if other factors are favourable to support snow.

Anyway wandering off topic here with this subject.

I don't agree.

Several years ago on the 29th nov I think it was we had easterly winds , uppers were -3 , that evening I watched the rain turn to sleet and then snow, we had about an inch of snow before turning back to rain, it was because of the due points been low aswell as evaporative cooling , that was living on ground 68 mtrs asl , my brother living in b'ham had 3inches that night. I understand if you live by the coast, but other than that uppers are not the be all and end all.

[chris55]

Last one from me on the 12z model runs; feel like my points are rather laboured today.

We can only comment on the output before us and in the last 24 hours (since the 12z runs yesterday) there has been a TREND by the operational model outputs away from any real cold advecting across the UK. We also now appear to have another shortwave palava on our hands; and this is exactly the reason I urged caution yesterday.

Long term we may see proper cold (low upper air temps & thicknesses) infiltrate the UK but within the next 8-10 days I think it's going to be a real struggle.

In this situation you can not take 8-10 day deterministic charts with any faith, either very cold or very mild. Just sit back and see what unfolds. You may well be right, but in all honesty unless we get consistent signals in the mid range they mean nothing. And at the moment beyond day 5 is all over the place,

Edited November 22, 2012 by chris55

[Snowy Easterlies]

what would happen if the ECM went past T240 would the PV ramp up and flatten the ridge or will some proper cold develop ?

[Geordiesnow]

The models will always struggle with the positioning of the Arctic high and associated troughs/Lows/shortwaves. The upcoming pattern is by no means a two day toppler and although in the past 10 years the said scenario was the most likely, the current synoptic pattern couldn't be further from that.

Its not but because of the lack of cold air available, we would get more snowfall from a 2 day toppler than this ECM run if it all happened on face value, which it won't of course.

Although I got lambasted by some for my negativity/concern at the lack of cold uppers, I do get a sneeky feeling from viewing all the outputs that we may struggle too see much snowfall in the future despite all the blocking. Yesterday runs were nearly perfect for this but it was still a struggle. Today's runs(apart from the GFS) has moved that more solid cold pool eastwards so we are even further away from any significant cold air.

As Crewecold says, its like pulling teeth to get any significant cold air further south and west, the cold uppers the models are forecasting for us are very patchy nature and may be too mild for any significant snowfall.

No one knows for sure how cold it may get just yet but one thing that does look more certain is that the northern hemisphere pattern will change to a more blocked one so its a wait and see process I'm afraid.

[Liam J]

I don't agree.

Several years ago on the 29th nov I think it was we had easterly winds , uppers were -3 , that evening I watched the rain turn to sleet and then snow, we had about an inch of snow before turning back to rain, it was because of the due points been low aswell as evaporative cooling , that was living on ground 68 mtrs asl , my brother living in b'ham had 3inches that night. I understand if you live by the coast, but other than that uppers are not the be all and end all.

Ok -3c uppers are fine under more persistent precipitation when evaporative cooling comes into play. Don't confuse this with the sunshine and snow showers regime in an easterly flow because it just wouldn't happen.

Enough off topic posts now.

Edited November 22, 2012 by Liam J

[nick sussex]

what would happen if the ECM went past T240 would the PV ramp up and flatten the ridge or will some proper cold develop ?

Unlikely it looks like hinting at retrogression and you have low heights in the Med.

As long as you have lower pressure in the northern Med its very difficult to get milder conditions into the UK during winter.

[cold snap]

this 850s argument runs on and on can fergie weather.john holmes or steve answer this correctly in pure english

many thanks

[tinybill]

http://www.meteociel...?mode=2&ech=204

http://www.meteociel...2&carte=&mode=0

all i saty if fantasy land comes off this place will go into melt down!! brimg on december!!

Edited November 22, 2012 by tinybill

[weatherguy]

I seem to recall from this thread last year that, when comparing an easterly to a northerly, you can get away with higher upper air temps?

Anywho, back directly to the models: Still showing a fantastic set up, it's easy to get hung up with the minor details, but looking at the northern hemisphere shows the big picture: MASSIVE northerly blocking continuing and thus an increased chance of colder weather in the long term. And indeed, even in the short-medium term, things look good pattern wise for us right here. Upper temps no need to look at just yet in great detail; get the pattern in place and the cold will follow if the blocking holds for long enough.

[Dexter29]

One thing we can say " a pattern change is underway and it's going to turn colder "

When and how intense? Who knows... 2 days ago the potential for snow was 8 days away... And today it continues to be 8 days away.

I do hope it won't continue in this vain, but we all know what a projected cold spell loves to do to us on each run..... DELAY

[chris55]

solid cold pool

That solid cold pool only first appears on Tuesdays 12z runs with the introduction of the Artic high into the mix, the Artic high is still there it is just the interaction with other features which either allow the cold uppers to come this way or not. But as we know this type of evolution is open to quite big changes at range.

Take the ECM and GFS at 192 as an example, both are not a million miles away from each other but the outcome fro the UK is marked,

http://www.wetterzentrale.de/pics/Rtavn1922.png

http://www.wetterzentrale.de/pics/Recm1922.gif

Modelling these small but significant changes at 192 is very difficult we need to wait until things come into the T96 range before we can bemoan the loss of the cold come T0.

[danm]

Very good GFS 12z ensembles: http://www.wetterzentrale.de/pics/MT8_London_ens.png

[Snowmad79]

this 850s argument runs on and on can fergie weather.john holmes or steve answer this correctly in pure english

many thanks

Did Steve M do a runner after the ECM 144hr chart ? Was hoping to see more of his analysis of tonight's runs.

For me, whilst the UKMO and ECM were nothing special, I have to remind myself that the change to cold is coming and what the models do show is a continuation of this and possible re-attempts at proper blocking. Real cold may well be "prosponed" whilst the over all theme of colder conditions continues rather than a full on non event or breakdown.

[I remember Atlantic 252]

One thing we can say " a pattern change is underway and it's going to turn colder "

When and how intense? Who knows... 2 days ago the potential for snow was 8 days away... And today it continues to be 8 days away.

I do hope it won't continue in this vain, but we all know what a projected cold spell loves to do to us on each run..... DELAY

yeah, in other words the cold is staying in FI, just hope on Sunday the cold is not still 8 days away

[Weathizard]

Very good GFS 12z ensembles: http://www.wetterzentrale.de/pics/MT8_London_ens.png

THose are the best ensembles we've seen so far on this ride, let's hope the ECM ensembles have some more promise, people too hung up on each run.

[Cheshire Freeze]

yeah, in other words the cold is staying in FI, just hope on Sunday the cold is not still 8 days away

Or even worse (and something that's in the back of my head),we miss the boat completely.

I'm still smarting after the late Jan/Feb 'event' and a plethora of other false dawns I've witnessed over the years. Getting cold to these shores is never easy and I was just thinking to myself earlier that some people who have muttered Dec 2010 need to realise we might not see another December like that for 50+ years. It was THAT special in terms of cold.

Edited November 22, 2012 by CreweCold

[Troubleatmill]

this 850s argument runs on and on can fergie weather.john holmes or steve answer this correctly in pure english

many thanks

John H has a fantastic guide on here for this subject, for me personally I use the 850-100 how

charts and look at dew points i.e below 0great charts very border line if you look at these figures, so many variables its amazing it ever does lol

Edited November 22, 2012 by arron123

[chris55]

Also to throw into the mix, I'd say we see "corrections southwards" on the models far more often than things being moved north, just a thought.

http://www.wetterzentrale.de/pics/Recm1921.gif

[Liam J]

Can I just drop this guide to forecasting snow in here which was put together by John Holmes, it may just answer some of the questions that constantly get brought up here regarding snowfall & uppers air temps etc.

[chris55]

Or even worse (and something that's in the back of my head),we miss the boat completely.

I'm still smarting after the late Jan/Feb 'event' and a plethora of other false dawns I've witnessed over the years. Getting cold to these shores is never easy and I was just thinking to myself earlier that some people who have muttered Dec 2010 need to realise we might not see another December like that for 50+ years. It was THAT special in terms of cold.

Be subjective, take the output for what it is. If it rains for the next three months then so be it.

Edited November 22, 2012 by chris55

[Bristawl Si]

One thing we can say " a pattern change is underway and it's going to turn colder "

When and how intense? Who knows... 2 days ago the potential for snow was 8 days away... And today it continues to be 8 days away.

I do hope it won't continue in this vain, but we all know what a projected cold spell loves to do to us on each run..... DELAY

It's 22nd November - the tastier charts are still 9/10 days away. That takes us up to 2nd December.

Winter aint really started, so why the distress-type post?

Grab a beer and chill out!