Model Output Discussion - Tuesday 20:25 -->

[Paul]

Please continue the model discussion here.

All the latest model runs are available here on Netweather:

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http://www.netweather.tv/index.cgi?action=modelcomp;sess=

Please note that this thread is for model based discussion only, we have several other threads available for more general chat:

Ramping thread

Whining thread

General winter/cold weather discussion

We also have a new model summary thread for a slower paced model discussion with the hope being that anyone who wishes to can summarise their views on each run, rather than discussing individual charts etc as they come out.

Please keep your posts on topic - and bear in mind the team will be removing the off topic ones whenever they see them.

[SNOW-MAN2006]

Well this all looks certainly very interesting.

Its been a while since ive posted on this forum probably a good year or so.... This is looking to shape up nicely and is certianly looking more and more plausible by the day.... but as mentioned numerous times before it is still a mile away, the building blocks are looking certain but in terms of the juicy stuff it is still a long way off.... ill be back on friday or saturday to review the situation!

My Charts of the day has to be most of the ECM and the JMA is looking very nice too. Even the GFS looks very nice in the short term but a very messy situation later on... but still prospects are there....

Ill be back friday, well either have our heads in our hands or well be getting the sledges dusted down and the de-icer at the ready....

Ciao,

SNOW-MAN2006

[nick sussex]

The updated ecm ensembles for the Netherlands:

http://www.knmi.nl/exp/pluim/Data/PLUIM_06260_NWT.png

Interestingly the operational run was one of the milder options for days 9 and 10.

The mean height comparisons show that although the ecm and gfs diverged earlier, later on they are quite similar for the overall pattern.

http://www.meteo.psu.edu/~gadomski/ECMWF_12z/hgtcomp.html

[Snowaddict]

Your wrong there. Check the key again to the charts. Your out by 5C on every count. (Add 5C I mean to say)

Thanks for the heads up on this The Eagle

It's hard to judge with the Icelandic charts really!

The boundary lines seem to be rounded but I would suggest at least 850's of -10 at T+192, because the initial transition to the -15 boundary lines is well into SE England...

It's always hard to tell from the Icelandic charts but if the scale is read from left to right then the previously mentioned values would be fairly alright.

In fact, if you look at Meteociel, you can see that 850's of -6 to -7 are into Scotland by T+168 so again it's hard to tell... The Icelandic site is not very specific.

http://www.meteociel...68&mode=0&map=0

EDIT: Thanks for the welcome back CH

Indeed, as the Eagle was saying, it does look like +5 could be added to each value but it's hard to tell really & depends on what way forward the scale is read.

Is there any other site that we can obtain the ECMWF 850's from in graphical form?

SA

[snowmadchrisuk]

Thanks for the heads up on this The Eagle

It's hard to judge with the Icelandic charts really!

The boundary lines seem to be rounded but I would suggest at least 850's of -10 at T+192, because the initial transition to the -15 boundary lines is well into SE England...

It's always hard to tell from the Icelandic charts but if the scale is read from left to right then the previously mentioned values would be fairly alright.

In fact, if you look at Meteociel, you can see that 850's of -6 to -7 are into Scotland by T+168 so again it's hard to tell... The Icelandic site is not very specific.

http://www.meteociel...68&mode=0&map=0

EDIT: Thanks for the welcome back CH

Indeed, as the Eagle was saying, it does look like +5 could be added to each value but it's hard to tell really & depends on what way forward the scale is read.

Is there any other site that we can obtain the ECMWF 850's from in graphical form?

SA

I would agree with your orig post snow , You were not 5c out on every count , I think you were spot on . Or you were to what them charts show.

Although just to add , them charts don't give you exact but if you can look on meteociel out to 168 and your first post wasn't far off.

Edited December 8, 2009 by snowmadchrisuk

[Glacier Point]

I would not say the teleconnectors are fully supportive right now of the cold pattern, perhaps 70% there.

The thing that is really going for high latitude blocking are the atmospheric teleconnections, more particularly a downwelling mean easterly zonal wind anomaly across the high latitudes (related to the earlier warming of the stratosphere in November):

http://www.cpc.ncep....OND_NH_2009.gif

http://www.cpc.ncep....OND_NH_2009.gif

This clearly showing up in GFS Arctic Oscillation forecasts, dropping off the scale within day 5:

http://www.cpc.ncep....ex/ao.sprd2.gif

http://www.cpc.ncep....ex/ao.sprd2.gif

At the same time, we are seeing a strong burst of mean west zonal wind anomalies across the tropics in the Pacific breaking down the ridge off central America and enhancing the sub-tropical flow consistent with Madden Julien Oscillation wave progression towards and past the Dateline.

http://cimss.ssec.wi.../waves-pac.html

http://cawcr.gov.au/...m/OLR/m.3d.html

Being picky I would prefer to see the centre of organised convection a little further east of the Dateline which accords with negative North Atlantic Oscillation phase.

The Global Wind Oscillation has yo-yoyed into phase 8: (possible explanation for 00z operational ECM)

http://www.esrl.noaa...gcm/gwo_40d.gif

However, there is a relative positive angular momentum developing in the tropics and sub-tropics as a result of poleward fluxing of west wind anomalies and relative and total angular momentum are trending upward.

http://www.esrl.noaa...g1-21.90day.gif

This will hold the GWO in a quasi stationary orbit around phase 4 (composites suggest blocking and low pressure in the Atlantic extending into Scandinavia) for the forseeable future, perhaps edging towards phase 5 in the lead up to Christmas (more low pressure but increasing tendency for height rises over Scandinavia).

So despite the teleconnections being not quite there, reasonable agreement for high latitude blocking and an increasing tendency for a solid -NAO pattern with height rises towards Iceland and southern Greenland. Tonight's GFS and CMC mean H5 height anomalies days 11-15 are in good agreement of the longwave pattern with the GFS ensemble mean being very aggressive in programming a 275m positive anomaly (block) centred over western Greenland / Davis Straights with the CMC not far behind:

http://raleighwx.eas...htAnomalyNH.gif

http://raleighwx.eas...htAnomalyNH.gif

Note the solid -AO / -NAO pattern being advertised there with the uppe lows in the Atlantic and Russia merging towards western Europe likely to set up a battleground scenario. This has support from the phase space (GWO) analysis.

So the best approach to tonight's runs would to agree with ensemble mean guidance from the GFS and CMC. This translates to a high probability for cold weather to take control within 10 days. How cold it gets will depend the initial draw of cold air from Russia and disruption of the flow but the general trend looks for high pressure to be centred over Iceland and Greenland with east / NE winds trending to swing more easterly as lows attempt to track in from the SW.

[chionomaniac]

I would agree with your orig post snow , You were not 5c out on every count , I think you were spot on . Or you were to what them charts show.

Although just to add , them charts don't give you exact but if you can look on meteociel out to 168 and your first post wasn't far off.

It will be easy enough to check with GFS charts from the Icelandic site and compare them to the NW charts.

[snowmadchrisuk]

It will be easy enough to check with GFS charts from the Icelandic site and compare them to the NW charts.

Yeah but i'm talking about ECM and netweather doesn't show the 850's out to +168 do they ? or am I looking in the wrong place.

[Rob K]

I would agree with your orig post snow , You were not 5c out on every count , I think you were spot on . Or you were to what them charts show.

Although just to add , them charts don't give you exact but if you can look on meteociel out to 168 and your first post wasn't far off.

No, he was wrong. Look at the scale.

From the right: red means 10 to 15C

Dark orange means 5 to 10C

Light orange means 0 to 5C

Yellow means -5 to 0C

Light blue means -10 to -5C

Next blue means -15 to -10C

and so on until dark blue means -25 to -20C

So the coldest air on the above chart is over Scotland and is between -5C and -10C (likely fairly close to -5C as it is close to the boundary with the yellow). The yellow air over England is between 0 and -5C.

The -5C isotherm closely follows the Scottish border, and also just clips East Anglia.

This can be confirmed by comparing with Meteociel: http://www.meteociel.fr/modeles/ecmwf/run/ECM0-168.GIF?08-0

That has -4C and -6C isotherms, not -5C, but the -6C covers NE Scotland only.

Edited December 8, 2009 by Rob K

[johnholmes]

.

I would agree totally with that Stewart-thanks for the in depth wider teleconnections links shown.

[chionomaniac]

Thanks for more great analysis GP.

Can I ask a question. What is the trigger that has got the polar vortex to split? My guess is that it is a combination of the weakened vortex state due to the warmth of the strat during November (combined with the negative downwelling anomalies) and the strong Pacific ridge that somehow caused the split. Would this be fair?

c

[mcweather]

Thanks for the update GP.

Looks odds on for some interesting weather.

I particularly like the bit about NE winds trending more easterly as low pressures attempt to track in from the southwest.

A snowy scenario if ever there was one.

[Snowaddict]

So the best approach to tonight's runs would to agree with ensemble mean guidance from the GFS and CMC. This translates to a high probability for cold weather to take control within 10 days. How cold it gets will depend the initial draw of cold air from Russia and disruption of the flow but the general trend looks for high pressure to be centred over Iceland and Greenland with east / NE winds trending to swing more easterly as lows attempt to track in from the SW.

GP, thanks again for this in-depth analysis.

Your reasoned & supported posts are always a great source of both knowledge and learning for all on the forum.

If & of course it's a big if, areas of low pressure do eventually approach from the southwest as advertised by the GFS suite several times, we could be looking at the potential for some significant snowfall with marginal situations etc..

[Frosty.]

..

Another great read there GP, thanks

It always gives my confidence in the models a boost when you provide posts like the above.

[Glacier Point]

Thanks for more great analysis GP.

Can I ask a question. What is the trigger that has got the polar vortex to split? My guess is that it is a combination of the weakened vortex state due to the warmth of the strat during November (combined with the negative downwelling anomalies) and the strong Pacific ridge that somehow caused the split. Would this be fair?

c

I'd cite the warming during November as being the primary factor Ed. By the way, wave 1 has peaked, possibly the second more progressive one to follow shortly. Then we have a large middle and upper tropospheric ridge centred around 70N. Next wave of mountain torques within 10 days. Net result - major mid winter warming before the month is out ?

[johnholmes]

okay Stewart so what caused the November warming

at least at 30mb it lasted well over a month?

[Bristawl Si]

Thanks for the update GP.

Looks odds on for some interesting weather.

I particularly like the bit about NE winds trending more easterly as low pressures attempt to track in from the southwest.

A snowy scenario if ever there was one.

Ditto! I don't pretend to understand all the aspects of GP's posts but the underlying message seems to be pretty good for cold and snow lovers. Still a long way off though from my reading of tonight's models, as to the 'real deal' a few days into any cold spell. I for one would not like a stale HP centred over the UK, with frost and fog and little else.

So the mention by GP of lows possibly approaching from the south west and then bumping into v.cold air by then, sends shivers down my spine

Edited December 8, 2009 by Bristle boy

[chionomaniac]

I'd cite the warming during November as being the primary factor Ed. By the way, wave 1 has peaked, possibly the second more progressive one to follow shortly. Then we have a large middle and upper tropospheric ridge centred around 70N. Next wave of mountain torques within 10 days. Net result - major mid winter warming before the month is out ?

That's what I thought. It is good to see that the favourable stratospheric conditions already having an influence on the winter so early in the season.

I checked out the wave forecasts earlier today and the ECM are suggesting a big wave 2 event next. I don't know how that fits in, but I certainly think think that the strat is there for the taking!

[Leigh]

Sorry to be really dim. What do the models show for us tonight? I have always read on here not to trust FI, but it seems in my little knowledge of weather that this cold spell is still in FI. Are we looking for trends, and what model should we now believe?

[johnholmes]

try my blog Leigh-it may help-and welcome to Net Wx-good time to join

[Rob K]

Sorry to be really dim. What do the models show for us tonight? I have always read on here not to trust FI, but it seems in my little knowledge of weather that this cold spell is still in FI. Are we looking for trends, and what model should we now believe?

Well although all the real cold is in "FI", what is important is that the progression to a situation that will likely deliver that cold has now been firmed up and is shown at about 96 hours, which is pretty well within reliable range. (Touch wood!)

By 96 hours, high pressure is starting to ridge northwards starting the process of moving up to Greenland/Iceland or thereabouts (exact position subject to change).

[leroys35]

if this warm wave happens and it causes the polar vortex to collapse what are the implications for the winter could we end up with a 1963 or 1947 winter any ideas guys

[mcweather]

Ditto! I don't pretend to understand all the aspects of GP's posts but the underlying message seems to be pretty good for cold and snow lovers. Still a long way off though from my reading of tonight's models, as to the 'real deal' a few days into any cold spell. I for one would not like a stale HP centred over the UK, with frost and fog and little else.

So the mention by GP of lows possibly approaching from the south west and then bumping into v.cold air by then, sends shivers down my spine

Me too Bristle Boy

http://www.knmi.nl/exp/pluim/vijftiendaagse/index.html

Excellent and very cold extended ECM ensembles tonight

[Duane S.]

I'd cite the warming during November as being the primary factor Ed. By the way, wave 1 has peaked, possibly the second more progressive one to follow shortly. Then we have a large middle and upper tropospheric ridge centred around 70N. Next wave of mountain torques within 10 days. Net result - major mid winter warming before the month is out ?

Cheers for that too GP. I asked the same question yesterday evening but I didn't time it very well I don't think. It was right in the middle of the 18z post-mortum posting frenzy!

I was impressed at how last month some had confidently predicted the PV split just before it actually did.

[DAVID SNOW]

Perhaps the deep solar minimum we are in is now starting to become the main driver re strat warming, more southerly jet,northern blocking. The LAG effect maybe upon us