swilliam

Even the NOGAPS looks ok - decent block at +144 Begins to undercut at +180

That is some jet coming out of the US

Seems the UKMO going with their model and not the ECM or the GFS although with the usual caveats about the uncertinty (who wouldn't)

For the medium, term cold we seemt o be reliant on the shortwave near Iceland dropping SE. It is about to happen on the GEM but did not do this on the GFS.

Control run FI is interesting in that it develops a sunstantial Sandi block - might bring some super cold uppers if we get suitable undercutting Sinks unfortunately

Nice looking ensemble mean at 192 - split vortex, artic high, ridges in the Atlantic and alutieans

But as you said yourself the ensembles past the initial high pressure building over us are showing a wide variety of solutions - inlcuding having the PV right over or near us and some very deep depressions (terrible for the flood risk areas by the way). So it is no suprise that the mean shows lower pressure there and therefore on average a positive NAO. The deep depressions are deeper below average there than the high pressure is above average in the mid atlantic block solutions. There are also more solutions of this type than blocked. So as I think SM once said to me the ensemble mean at that range is about as useful as a chocoate teapot. As long as some blocked options keep appearing I would not worry too much.

Look like the Northerly has gone though

Hi John, It seems, in this thread at least, anything that is not cold (enough for snow) is called mild or even very mild. I got told off for pointing this out a couple of days ago when someone said Christmas was going to be very mild when in fact the model predicition was for near or slightly below normal. Stewart

Lots of really good members but what is more impressive is the clustering.

Control run from the GFS is looking very nice in FI.

Doesn't look in the very mild catergory to me except in the far S (even then just above average).

Looking at the GEFS is seems pretty solid till the 13th then after the 16th anything could happen Here in N Sweden (lulea) no problems. -14C and light snow with breeze. Major snow in Stockholm yesterday due to heavy snow causing problems geting here

I think we want the low heading NE out of NA to head upthe W side of Greenland like it did on the 06 (and not underneath it)

The difference is the trough to the S of Greenland is less favourably aligned to disrupt - let's hope it does though.

The wind speed does have an effect on the actual temperature in an Easterly. With a slack flow the N Sea has a large influence - increasing both the dry and WB temps. With a strong wind the air from the continent has less time to increase in temperature so it is colder as a result. The direction is also important. If it is SE then there is a short sea track but this increases as it becomes E and then NE. This increases the temps but also increases moisture and convection producing more precipitation. The big advantage of low uppers is that we can get large amounts of convection and this remains as snow even on the coast.

If you bug him with will it snow in backyard questions every times he posts then the result will be that we will not get this inside info.

Well ECM is very similar to the UKMO at t14 so I guess we will get to see it might evolve from here.

I really do think people should stop guessng what will come after the UKMO 144. Looking at it those small LPs they could move in a variety of ways and we will never know who is right/wrong as it is extremely unlikley to verify exactly like this anyway. None of the models are showing the link up at this juncture so I do not know why people think the UKMO should. Also remember that IF said last night that the UKMet do not use their GM beyond day 5 anyway.

The CFS is giving the vortex to us for Christmas

Except they then appear in someones irritated reply to them - can we switch someone's reply to an unwanted poster off as well?

I must say there are some rather silly posts on here tonight; talking about how can the ECM be so far out, saying it is a battle between ECM + minors agsinst GFS/UKMO and depending on the outcome one is right and the other wrong etc. There are two basic solutions for the period t120-144. One is that we have extensive blocking to our N and a cold solution for a protracted period (i.e. GFS/UKMO). In this case the Canadian low goes N/NW up the W coast of Greenland and does not send enough energy eastwards to break the Atlantic ridge. Eventually this minor remnant energy moves SE as a potenial slider. The other is that the Canadian low sends energy eastwards and does not go up the W of Greenland - a small difference in positioning of this low. This energy then breaks the link between the Atlantic ridge and the N blocking. The result of this is the Atlantic ridge falls over and the energy from, and substantial remnants of, the Candian low link up with euro low and we end up with mildsih westerly winds over us. Blocking and splitting vortex remain to the N but we loose the blocking in our immediate vicinity (only). Thereafter there is the possibility of blocking reestablishing near to us. The differences between these two solutions is very small and therefore marginal but the consequences for our weather >t144 is massive. So whichever way it goes (and no-one knows at present) does not mean one model got it hugely wrong or right - both options are quite plausibe at present - further small changes will determine which way it goes. These two solutions have been showing on the ensembles in the last few runs and on one or two of the GFS ops (when it was derided). Some less hysterical or emotional posting would make this thread rather more enjoyable.

Short term 18z ensembles look rock solid for cold

Would be some interesting weather for Canada if something like this happened

HI John, I am not sure that the models do have more difficulty with depressions from this direction - it is just that small changes have large effects on the weather (especially in Southern England but we won't go there). If you look at a typical depression most of the weather is to the S of the centre. Typically there will be fronts dangling many hundreds of miles S of the depression often with strong winds and following on behind a large area with showers. So if one of these depressions moves to the North of Scotland most of the UK will get a spell of wet and windy weather followed by showers. The forecast is easy and if there is small variations in the track of the depression nobody notices much. To the N of the centre of the depression though the area of rain and strong winds is often aligned either SE-NW or even E-W associated with the occluded or occluding fronts. This area of rain is therefore aligned with diorection of travel so if the depression track varies by relatively small amounts the change in the weather in a particular locality can be quite marked. The result is that the changes in the track of the depression are noticed much more - like the one on Sunday. This can be seen on the fax chart for Sunday. The depression in question extends all the way from N France to S Portugal so for most of France small changes in the track will have relatively little effect on the weather. Near the depression centre though the fronts are aligned E-W (the same direction that the depression is travelling in) so small changes in the path will have a big effect on the weather in the extreme N of France (and also of course S England). This general effect can be seen even more so for the deep depression near S Greenland. If you happened to be living on the tip of S Greenland (plenty of interesting weather there I should think) then the track of this depression would have a major effect on your weather. To the S of it though the weather is essentialy the same for more than a thousand miles - so you would not care to much about track - it going to rain and then there will be heavy showers. Having said all that the tracks from this area may be somewhat less predicatble for couple of reasons 1 - The depression coming from this direction are often rather small with a low overall energy and so can have tendency to wander - e.g. Sundays depression 2 - Similarly and probably because of this they are often associated with a rather weak jet so the direction is less well determined. This can be seen by looking at the jet profile for Sunday The jet with this depression is quite weak so the steering is not very forceful. Compare that with the much more energtic low to the S of Greenland - here the jet is very strong and everything will probably be quite predictable with this system.