cooling climate

I still think the ECM is making a little to much of the shortwave at t120 which effects the rest of the run but a very good run never the less.

Much better run than the 0z with better heights to the north. Actually not that big a difference to the GFS at t144.

After a very quick look at the ensembles I would say 80% now go for a very cold outlook. Another day or two at the most and then I think you could call this a lock.

Who would have thought out to t96 and even better ridging than on the 06z run. Could be another belter on the way.

If the UKMO and GFS 06Z are correct at t144 then its definitely game on. The BBC weather man at 13.30 said high pressure could be around for some considerable time to come from this weekend onwards. Everything further west at t72 very good signs.

I have just been reading up on shortwaves (3) decreasing the mass of the air (i.e. upper level divergence). Causing the air to rise counteracts some the downward force created by gravity. This lowers pressure just as if someone started pushing up on you when standing on a scale; your weight would decrease. Fronts force the air to rise. This causes the surface pressure to decrease in the vicinity of the front. Cold fronts have a more defined pressure trough than warm fronts because the average cold front has a steeper slope and stronger temperature gradient than the average warm front. A warm front raises the air gradually while a cold front lifts the air more quickly in the vertical. The faster the air rises, the more pressure will lower. A mid-latitude cyclone and a front will both cause the air to rise and pressure to lower. The stronger the front, the more well defined the pressure trough will be. Now to shortwaves. A shortwave is an upper level front or a cool pocket aloft. Just as a surface front causes the air to rise, upper level fronts can do the same. First, let's start with a general description of a shortwave: (1) It is smaller than a longwave trough (shortwave ranges from 1 degree to about 30 degrees in longitude (the average one is about the size of two U.S. states put together (Iowa and Missouri put together is a good example) (2) Isotherms cross the height contours (if it is a baroclinic shortwave). This creates an upper level temperature gradient and therefore an upper level front (3) They are best examined on the 700 and 500 millibar charts (4) They generate positive vorticity (mainly due to the counterclockwise curvature within the shortwave). This creates positive curvature and positive shear vorticity. If PVA occurs with the shortwave then the shortwave will deepen and strengthen due to lift created by upper level divergence. (5) They can create an environment conducive to surface based convection or elevated convection due to the cooling aloft. It is important to see how much moisture is associated with the shortwave. A shortwave moving over a warm and moist lower troposphere has a better chance of producing precipitation and strengthening than one moving over a dry lower troposphere. If the low level dewpoint depressions are low, the instability and lift associated with the shortwave can enhance cloudiness and precipitation. In summary, a pressure trough is associated with a low-level front while a shortwave is associated with an upper level front or a cool pocket aloft. Both are associated with rising air and can add instability to the atmosphere. The diagrams below show an upper level shortwave and a surface pressure trough. The pressure trough is the kinking along a front. google_protectAndRun("ads_core.google_render_ad", google_handleError, google_render_ad); If I have understood it correctly then I would say that in the model time frame of t120-144 it would be more probable to get a shortwave develop on the east side of the ridging high where you also have the largest temperature gradient. I am confident now there will be no spoiler shortwave development but rather one on the Scandinavian side that will aid in the CAA westward toward us.

The ECM does not look plausible in the t120- 144 time frame therefore I would expect to see this come on board with the GFS and UKMO this evening.

Stratus Group: Members Posts: 167 Joined: 11-November 09 Gender:Male Location:hertfordshire Posted Today, 08:57 With such large discrepancies between the ECM and the UKMO charts at t144 on the n/hemisphere charts regarding blocking over our side of the Arctic means things are far from settled. Lack of data and monitoring equipment is a problem as we know when it comes to modeling the high Arctic but I do think that the ECM has been way over progressive in breaking down the block. If you look at the time frame t120-t144 where a piece of the vortex cuts into the block which has a knock on effect of shunting everything southwards in our direction, looks completely implausible to me. Steve Murr may well turn out to be correct in his fears of shortwaves running through the block and spoiling the party we shall see but the UKMO is not so keen on this idea, neither am I. http://www.meteociel...72&mode=1&map=1 The ECM looks to be on its own regarding the vortex energy breaking down the heights. This should be a cracking run now.

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

With such large discrepancies between the ECM and the UKMO charts at t144 on the n/hemisphere charts regarding blocking over our side of the Arctic means things are far from settled. Lack of data and monitoring equipment is a problem as we know when it comes to modeling the high Arctic but I do think that the ECM has been way over progressive in breaking down the block. If you look at the time frame t120-t144 where a piece of the vortex cuts into the block which has a knock on effect of shunting everything southwards in our direction, looks completely implausible to me. Steve Murr may well turn out to be correct in his fears of shortwaves running through the block and spoiling the party we shall see but the UKMO is not so keen on this idea, neither am I. http://www.meteociel.fr/modeles/ecmwf.php?ech=72&mode=1&map=1

The GFS model is doing its normal built in flaw with the shortwaves here's hoping that both GFS and the ECM are more in line with the UKMO at t144 then we can rest much easier.

On the n/hemisphere charts you could see that this run was not going to be as good (although a lot better than last night) due to the fact that pieces of the vortex or lows are running across the top of the high thus sinking the high south. This did not happen on the 12z GFS, ECM or UKMO. This is the 18z so I would keep a very open mind.

I really think that the - AO is running the pattern as regards to heights being pulled north and the atmosphere backing west due to the easterly inertia caused by the -AO. I am sure i will get this post thrown back at me if I am wrong but if the Arctic oscillation goes as negative as is being suggested and we get the WAA and height rises shown at t144 (I think the UKMO and GFS are more on the money here) the following very cold patterns shown by the models will be a certainty.

ECM T216 excellent.

ECM at t192 SUPERB. lol

ECM at t168 is a belter.

Not in a month of Sundays.

Just because we have not seen synoptics as good as this since 95 or 81 does not make it unrealistic. UKMO has better ridging because it has done away with the shortwave on the GFS run at t144 around Greenland. Therefore I think the UKMO would lead to an even colder run than the GFS.

UKMO is superb.

I mentioned yesterday about the models having a wobble but I must admit I did not think the GFS would come round this quick.

The parallel has a reload and wants to continue the freeze through to the new year by the looks of things.

Give it another few runs and I think that troublesome shortwave at t144 will be downgraded or the model will ditch it altogether. If this does happen it will bring the colder air in quicker but we still need a trigger for the bitterly cold air to the ne. lol I see that the troublesome low is the trigger for the bitterly cold air avecting southwestwards.

Better ridging north and things starting to look a lot less complicated wont say much more as I don't want to put the mockers on it.

This is what has happened over the Pacific and Alaskan side which has resulted in SSW and is responsible for the upcoming -AO I think.

That is the way I understand it also. It is a vorticity chart and the greatest vorticity will be centered around the vortices's.