Winter Model Discussion 18Z 5/2/13 onwards.

[Frosty.]

okay folks I give up TRYING to reason with some of you who dismiss my attempts to explain what we can and can not get from close and careful scrutiny of upper air charts, principally the 500mb anomaly charts.

I have better things to do than keep saying the same thing, sorry, I will restrict myself to the more detailed thread where as promised I will post the pdf trying to explain these charts in more detail.

This is not toys out of prams but I have tried long and hard with great detail over about 14 months to show how they can and do give great guidance for major wave length changes 1 to 2 weeks in advance of them occurring. The data is there for anyone who wishes to go through, I think, 30 or 31 case studies from January 2012 to December/January this year.

who is dismissing you john? certainly not me : )

[Brassneck]

the control run has the same starting data as the operational but runs at a lower resolution to T192. thereafter, the op runs at a lower resolution to the control but at more horizontal atmospheric layers. if the control and operational both resemble each other through the post T192 timescale, there can be a bit more confidence in the general pattern shown by the two runs.

Thanks for the explanation.

[latitude]

Anomaly charts - not height charts. Again this has been pointed out numerous times that an anomaly is just that.

And the anomaly for the first to months of winter so far at 500 hPa:

It is not the anomaly chart that has the error - moreso your ability to read them correctly.

Edit: note to self read through the thread further to see if anyone else has made the same point!

Thanks IF and JH

Thank you for your replys. Seems I am confused by anomoly and heights. Anyway, there hasent been any High Pressure across Greenland producing a blocked Atlantic scenario. This was touted all winter....still we are waiting for it.

[bobbydog]

I couldn't resist showing you this (may help to put across the other side of the story):

ECMWF snow cover projection by Midday Tuesday (I have left the scale off as I have never found this especially accurate from the source I use)

And the control run:

SK

always nice to see lying snow on the sea!

[SMU]

it shows how people can read chionos anomaly chart as the date is wrong.

No way that much polar anomaly!

[Ian Brown]

The weather looks like exploding into life during saturday night and sunday with potentially large snowfalls across the uk and colder air being sucked into the lows circulation from the east, it's like a cold bomb and it's big and it could bring the heaviest most disruptive and prolonged snowfalls of this winter so far and that is saying something since we have already seen some very snowy weather in certain parts of the uk during the last freeze in January. I think the gfs is modelling the low too far north, it seems even further north than the 00z and the ecm 00z shows it further south but I think most parts of the uk could have at least some snow between sun and tues and the high impact areas could become snowbound before that low fills and clears away southeast, the 6z shows a standoff next week between the scandi high easterly and the atlantic trying to move in.

The azores ridge looks like collapsing rather quicky during saturday and then we are in for an action packed period with snow again dominating the headlines.

I think that is a rather dramatic assessment Frosty for an event that could be a messy mix of rain, sleet and snow. Higher ground will be favoured obviously but as for which higher ground there is still too much uncertainty to say.

There were quite a few events in the eighties where rain would turn to snow, then as you see the dewpoints fall the ground appears to dry out before the snow starts to settle. But as things stand if you are going to see snow you are going to have to see rain, and perhaps quite a bit of rain, first.

Beyond the early part of next week, I would have slightly less confidence than I did yesterday of an Atlantic return but would still see such an outcome as the much more likely than anything else but we will see what Exeter make of the data that they have combined with the EC ensembles.

[Ryan Dutch Weatherman]

En there is the another glide low,.

Brazilian model 00z.

Your wisch is my command.

[Frosty.]

So where is the Atlantic?

http://www.wetterzen...s/Rtavn3121.png

Cold spell still going strong into the following week.

Have to say some poor analysis from some today, very poor infact.

I think it is more to get a reaction, and sadly it always works.

[SomeLikeItHot]

Please I beg do not get pulled into this upper air debate , the upper air at this range is not even worth commenting on , look at the bigger picture , good signals now going forward .

Not quite sure what you mean, perhaps I have missed some discussion that has occurred here previously.

I agree its a good signal, but is the statement wrong? The air pool we are drawing from is warmer than usual, and although we can't know the outcome exactly it seems likely to be less cold than we would normally expect from an easterly flow.

[chionomaniac]

Thank you for your replys. Seems I am confused by anomoly and heights. Anyway, there hasent been any High Pressure across Greenland producing a blocked Atlantic scenario. This was touted all winter....still we are waiting for it.

I think in fairness that next year, when GP releases his winter forecasts, he should spend some time explaining the difference between the anomaly charts posted and the expectations that these may give others. I suspect that I have been guilty of that myself in the past. For example, a positive H500 anomaly over Greenland would have to be vast for a true GH to form. A slightly positive anomaly would lead to a slightly reduced polar vortex in that area which would still give a zonal pattern.

[LomondSnowstorm]

it shows how people can read chionos anomaly chart as the date is wrong.

No way that much polar anomaly!

The dates aren't wrong Steve, it's a US site so 12/1 mean the first of December. For some reason when you plot it the scale is toned down (perhaps because height anomalies haven't been all that strong anywhere in the NH) compared to what it comes up with for other years but there has been a reasonably positive anomaly to our north for most of the winter so far.

[chionomaniac]

it shows how people can read chionos anomaly chart as the date is wrong.

No way that much polar anomaly!

No it isn't, you can produce the same yourself Steve

http://www.esrl.noaa.gov/psd/data/composites/day/

Month/day/ year in that format don't forget.

Edited February 7, 2013 by chionomaniac

[Frosty.]

I think that is a rather dramatic assessment Frosty for an event that could be a messy mix of rain, sleet and snow. Higher ground will be favoured obviously but as for which higher ground there is still too much uncertainty to say.

There were quite a few events in the eighties where rain would turn to snow, then as you see the dewpoints fall the ground appears to dry out before the snow starts to settle. But as things stand if you are going to see snow you are going to have to see rain, and perhaps quite a bit of rain, first.

Beyond the early part of next week, I would have slightly less confidence than I did yesterday of an Atlantic return but would still see such an outcome as the much more likely than anything else but we will see what Exeter make of the data that they have combined with the EC ensembles.

you will have noted I mentioned the potential for large snowfalls, the models are still firming up on sun/mon. We shall soon find out but i'm rather looking forward to what could be a big event, at least the gfs has finally come to the party.

Edited February 7, 2013 by Frosty039

[SMU]

ok well maybe my mistake i will have a look at the reanalysis charts later. With a mediocre winter so far and similarly average ao index im surpised at that image.

But will happily comment if i was wrong

s

[bluearmy]

the extended london ecm ens have now topped out around 5c in week 2 and indeed show a drop at the end. thats is line with what some of us saw on the de bilt ones yesterday evening. we should expect to see a firming up over the next few days as to which side is favoured to come out on top. the momentum currently with the block to our east rather than the atlantic though that can easily change (the 06z gefs v the 00z gefs in T200/T240 area a perfect example).

[Frosty.]

En there is the another glide low,.

Brazilian model 00z.

Your wisch is my command.

E P I C they make good coffee too.

[Ryan Dutch Weatherman]

Again the CFS model 18z en now the 00z is supporting my vision als for a very cold march 1e decade with lof of snow.

-14 at 850 HP in Engeland.

Look at this , look at this , were is the Atlantik !

CFS 00z.

CFS 18z.

1 March 2013 , winter start in UK .

[Tim Bland]

I couldn't resist showing you this (may help to put across the other side of the story):

ECMWF snow cover projection by Midday Tuesday (I have left the scale off as I have never found this especially accurate from the source I use)

And the control run:

SK

Reinforces what I said earler that many in the south / south east are fretting but somewhere like Chilterns / Cotsworlds Could get the largest totals IF the low stalls in the channel.

[Tamara]

Look the pluim for my country Netherlands noord.

Wenn there was a strong Atlantik like some people here say , than why i do see different.

Becouse i dont live pacific , i live near Brittain , if there was strong atlantik , my country EPS would also notice that.

There is an obvious spike there on the 11th from the operational and if we try to get a visualisation of that from the postage stamp members we can see that the northward thrust of the low on the operational and a few ensemble members is countered by quite a lot of support for the low to be very slightly further south by t96 to t108 (up to the middle of Monday where that spike shows up) This would suggest to me that the colder uppers may be further south east by the time suggested.

Although the graph ensembles are for The Netherlands, we can also assume that in terms of the low positioning it could mean that the colder uppers on the northern flank of the low would be displacing any warmer sector away quite quickly in SE UK as well. Indeed the warm sector itself in terms of size and extent may be more underplayed in the ensembles themselves.

http://www.ecmwf.int...0700!!chart.gif

Edited February 7, 2013 by Tamara Road

[mulzy]

There is an obvious spike there on the 11th from the operational and if we try to get a visualisation of that from the postage stamp members we can see that the northward thrust of the low on the operational and a few ensemble members is countered by quite a lot of support for the low to be very slightly further south by t96 to t108 (up to the middle of Monday where that spike shows up) This would suggest to me that the colder uppers may be further south east by the time suggested.

Although the graph ensembles are for The Netherlands, we can also assume that in terms of the low positioning it could mean that the colder uppers on the northern flank of the low would be displacing any warmer sector away quite quickly in SE UK as well. Indeed the warm sector itself in terms of size and extent may be more underplayed in the ensembles themselves.

http://www.ecmwf.int...0700!!chart.gif

No spike (for 11th) shown here - in fact these are the best London ECM ensembles in a while.

[snowmadchrisuk]

Issued at - 07 Feb 2013, 11:38

Valid from - 10 Feb 2013, 00:05

Valid to - 10 Feb 2013, 23:59

There is a risk that a band of rain spreading from the southwest during Sunday will turn to sleet and snow. There is the potential for accumulations up to 10 cm in places and the public should be aware of possible disruption to travel.

[MR EXTREMES]

if we go with the met office warnings then 20cm over 2 days could be on the cards but its a ever evolving pattern.

http://www.metoffice.gov.uk/public/weather/warnings/#?tab=map&map=Warnings&zoom=7&lon=-0.50&lat=51.35&fcTime=1360152060

[Barking_Mad]

Again the CFS model 18z en now the 00z is supporting my vision als for a very cold march 1e decade with lof of snow.

-14 at 850 HP in Engeland.

Look at this , look at this , were is the Atlantik !

CFS 00z.

CFS 18z.

1 March 2013 , winter start in UK .

haha love it, the laughing smileys nearly made me spit coffee on my screen

[chionomaniac]

ok well maybe my mistake i will have a look at the reanalysis charts later. With a mediocre winter so far and similarly average ao index im surpised at that image.

But will happily comment if i was wrong

s

No probs.

Yes, I do agree that the anomaly charts do look as if we should have been locked in the freezer all winter. The AO has been negative all winter though and matches well with these anomalies.

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/monthly.ao.index.b50.current.ascii.table

[MR EXTREMES]

Again the CFS model 18z en now the 00z is supporting my vision als for a very cold march 1e decade with lof of snow.

-14 at 850 HP in Engeland.

Look at this , look at this , were is the Atlantik !

CFS 00z.

CFS 18z.

1 March 2013 , winter start in UK .

indeed there would be a sting in winters tail for sure if this happens.

i also see someone comment yesterday how they have nevver seen snowfall at easter i have and i live on the south coast i remember april 3 or 4 years aco lying snow for a day very nice suprise very unstable arctic northerly that year.