swilliam

You just do not what is going to happen once the cold air is established. All kinds of small features develop and produce snow. There is also still the possibility of channel lows (as is alluded to by the UKMO 15 day outlook). The GFS control has a very nice example at T216. So I would not get so down yet. One thing is for sure - no cold = no snow.

Because it is a numerical model! As for the beeb back tracking they have consistently said that there is a lot of uncertainty at the moment- what else do you want. They are going with their high res models and other information and calling it as they see it at the moment. They also can see the discrepancies in the low res models and are allowing for that.

Yes, from the kink in the isobars the NAE model has the front running from the Severn Estuary to the middle of East Anglia, on the fax it is in the English channel but the fax chart is 6 hours earlier so probably consistent.

For those who were hoping next weeks event was going to be like Dec 31 1978 if you look further down the evolution of the GFS it is clearly illustrated how if we get the cold air in place then it is very likley to happen. Looking at the T162 chart we can see a small channel trough. But this produces plenty of precipitation And nearly of this will be fine powdery drifting snow if you look at the 850s of -5 (with a huge gradient), temps and dewpoints widely below zero and a NE wind of >15kts. This event lasts for the best part of 24 hours so you could expect large snow totals. On this run this is followed by the very cold Easterly blast so lying snow for days. So the point is that all models are showing the protracted cold spell and once this is well established there would almost certianly be snow for everyone. This would include those in the South who are fretting about next weeks event. I would say have patience and something interesting is almost certain to come at some time during the spell.

The GFS has it quite cold in Moscow into the New Year! Due to some quite low 850s

You were quite happy with the GFS when it (the parallel now the OP) was relentlessly predicting the pre-Christmas spell though? The ECM ensembles are excellent and as you say there seems to a major discrepancy with the GFS ensembles. These seem to have changed over the last couple of days. This is the ensemble group for four days ago and you can see after the 4th Jan there is a wide variation of solutions with the mean around -4. Comparing this to the current ensemble for the same period the mean is now approaching zero. What is also different though is that most of the members are tending to a mild solution but there a few with extremely cold solutions (keeping the mean down). So it seems that the chance of cold are reducing but that if we do get it it could well be more severe. Lets hope the GFS ensembles start moving towards the ECM which is already showing mostly very cold solutions.

ECMWF model to 240 hours Rating meteorologist Sunday, December 27, 2009 09.49 hours, valid from Monday, December 28 to Tuesday 05 januari Synoptic development The focus has to do with a southwesterly flow over. The layer responsible for the flow around Ireland attracts the north east coming days and will at the beginning of the week for a temporary westerly flow. A low pressure area over the ocean east and pull remains lie southwest of the United Kingdom. A core pulls east on Tuesday for the Benelux and provides an easterly flow. Simultaneously drops a new low height above the ocean south and ensures that the flow is again southwest. This low altitude over the next weekend Benelux attracts then further east. After passage over the northern flow. Model Assessment and uncertainties DThe uncertainty is particularly great because the focus is close to an air mass boundary where small differences yield a completely different weather. This process takes place in the coming period on two moments off. The first was Tuesday when our country is in a saddle area and a failure to pull the Benelux. The second time is next weekend, when a low pressure core of our country attracts. For both events is that small timing differences or position have significant impact on the weather. There is only 1 tube is present. This indicates that the diversity in the solutions is not as large scale is very large, but clearly (also seen in the plume, especially on Tuesday and next weekend so) that there are several possible solutions. Since even small differences in our surroundings has a major impact on the type of precipitation at temperatures around zero. The cluster plates allows the bulk of the members (90%) a more or see more westerly airflow over. Even here in the assessment should be included in the model that the snow is not good. In the initial situation in our country is still at least 20 cm, with also a relatively large area with 50-100 cm. The model is really not that snow melt away until Tuesday. This has very much influence on the temperature in the saddle area for at least Tuesday night! Notes to adjustments in Table Temperatures at the beginning incremented (both Tx and Tn). Summary multiple day period Many clouds and precipitation from time to time, starting Tuesday with a winter nature. Afternoon temperatures gradually lowered, the night's most progressive light frost. Summary period EPS Probably a transition to a more winter weather with temperatures slightly below normal values. Sorry about the translation but this was done by Google not me. When you cut and paste the page you get both the Dutch and English. I have deleted the Dutch for you this time. To find this you need put KNMI in Google and ask it to translate for and the navigate to the ensemble page. If you go direct to the KNMI site and use their English translation the discussion pages do not seem to come up (unless I have missed something). Could be useful when we want a professional opinion about the models. It seems they have a large area with >0,5m of snow and think this will have a major influence on the next weeks weather. They are also saying that there is a lot of uncertainty boty for next week and the following weekend. 2nd there is also a detailed 48 hr discussion <br style=""> <br style=""> Weer Weather Models generally 48 hours Rating meteorologist Sunday, December 27, 2009 08.41 pm, valid until Tuesday, December 29, 2009, 00 UTC. <br style=""> <br style=""> Guidance weather for the Netherlands, the Dutch coastal waters and the North Sea based on the HIRLAM run from 00 UTC and the other models listed and directories associated with runtime. Assessment Models Synoptic SITUATION: A low pressure area west of Scotland the next day to pull the North Sea and then to the south of Scandinavia. Associated cold front lies over the Frisian Islands. Golf Training over English Channel makes the front pulls slowly eastward. This afternoon in front pulls the declining activity over our country to Germany. In the night from Sunday to Monday passes the occlusion of previously known low and the flow turns to northwest. After we benefit from temporary high pressure influence. MODEL ASSESSMENT: The output is consistently large. The pressure and precipitation fields show great similarity between EC18, UKMO00 and GFS00. In the boundary layer, there are concerns. Considerations WIND: WIND: Along the West Coast 6 to 7 Bft. Monday coast no longer signals. CLOUDS: Increasing clouds on the approach of cold fronts (including ST). Near the cold front with high CSF basis (potentially unstable). Sunday (especially in the afternoon) in the entire country several CSFs. Monday spells behind the occlusion with a single CB (peaks FL200). For HiRLAM fog late Monday night and ST arise. This seems unrealistic because HiRLAM too cold (see merged time series). There is probably a snow expected. RAINFALL: Scattered showers extending over the next day the country. Suggestion of sleet / freezing rain in NESO fields. We honor not because the models are too cold. When it is cloudy, the temperature drops are not as strong. Possible smoothness by opvriezing during spells. : VISION: Well.In moderate rainfall. TEMPERATURE: Hir DMO is too cold (see merged time series). Prog Temps have a stable thick cold layer. In the source region is less windy and colder than in the Netherlands. KTG provides a good indication. Tx Sunday around 5 degrees. Tmin monday 3 degrees, Tx Monday, 4.6 degrees. I like the golf training over the English Channel<br style=""> <br style="">

Just looked through the 18z and thought gosh that is terrible from a long term cold perspective -particularly this horrible looking Southerly at T192 (by the way I am I the only person that ever puts up a chart now to support their discussion - it seems a lot of people of got lazy with only one or two liners such as upgrade/downgrade LP more S/N/W/E etc. and nothing to illustrate their point). But having had a chance to look in more detail I actually quite like this kind of evolution. It rather unrealistic to expect 2 weeks or even a month of cold across the whole of the UK - a simple look through the records will tell you this. There have only been a few occasions when this has happened. The next best thing is for the pattern to alternate between mild and cold and is probably something we should expect in most places. Next weeks event has been likened to the Dec 31 1978 event and then the 78/79 winter looked back on with fondness. My recollection of that winter (I was in Egham in Surrey) was most clearly that there were periods of cold (with some ice days) with snow - this lasted for a few days then there was a period of mild - maybe up to 2 weeks, then a renewal of the cold and more snow. So no continuous period of cold. The 18Z looks very similar to this with next weeks event, then the cold NE wind the the next LP and the Southerly (with snow at first). This is then followed by a very cold easterly (which I would like) with very low max temps and probably some nice dry powdery snow instead this marginal stuff. This is the followed by the Scandi high sinking but still plenty of potential for further outbursts of cold. You can see the -ve AO and the split PV on the NH chart at T384 - so more to come. So all in all this kind evolution look pretty good to me and would provide lots of interest for us as well as some major weather events. Finally I would just like to reiterate that the battleground event next week does not look anything like the Dec 31 1978 situation as I discussed previously. It is much closer to the Jan 1982 event when there was a lot of rain in England and not much snow. Cheers Stewart They have been showing this all day.

In the 'normal' format it can be seen that in FI the OP was very much on the mild side and the control went off on one again (much like the GFS control) - demonstrates the possibilities for this spell though. So I think we should delay the razor blades for few more days and see what happens. BTW I do not think the position of the low next week has a massive effect on the prospects for long term cold. It is more to do with the following depression, how much WAA it induces over Iberia/France and whether this links to the block from Greenland via the ridge over Scandinavia (i.e. as shown on the GFS OP). It seems to depend on the orientation of Greenland high. All very plausible but pretty marginal as to whether this occurs or not but has huge effect on the longer term prospects.

The De Bilt ECMF ensembles are out. Still a very strong trend downwards.

Still there on the control but this time it does not sink the high - what a difference!

Very annoying - it sunk our high - but it seems to be showing up on the all runs now including the METO T144

What scuppers it is the low coming under the block and generating hts over Iberia/France - like this run has just done. What is helping this time though is the block has extended from Greenland across to Scandi

I think there may be a better chance of getting the Easterly shown on the GEM on this run . The Siberian high is better aligned and the LP near Norway is less deep - we shall see.

I think the main factor determining how far the low gets North and the angle of the extended trough is how much pressure is put on them by the HP ridging from the North. Looking at the UKMO chart we can see that there is none of this at all. Compare this for example to the GEM at the same time The difference is marked. This has the advantage of tightening the gradient and probably increasing the intensity of the precipitation. More importantly though it increases the rate and intensity of the undercutting of the cold air. This would mean that many places would see snow rather than rain. The UKMO chart to me seems to indicate mostly rain - even in the North and especially anywhere near the East Coast. As I have suggested previously this looks quite a marginal event really and it certainly relies on reinforcement of the cold air from the far North. Another issue is that with the LP further North and poorly aligned we run the risk of not getting our extended cold spell as Kold has discussed. It is essential that the LP moves East after generating the large amounts of precipitation. To do that it needs to be engaged with jet stream that will be running through France If the LP is to far north and/or West there is a danger that it will stall and fill out near SW Ireland. This is evidenced already by the UKMO chart for T144 You can see the LP has moved slowly North and does not show much sign of moving East. The 2nd possible problem is that if the LP is too far North this pushes the block further North and as Kold has suggested we then run the risk of a LP from out West coming through the South of our block. There is evidence of this beginning to happen on the UKMO T144 as well. This could be a good thing in that we may get another battleground (assuming the cold air has flooded over us) or it could end the cold spell completely. So I think it would be good if we had less discussion about snow in the North v South and concentrated more on making sure we get a real snow event and also get the extended cold spell that would, in the end, give us all some snow Stewart Sorry about the extra map - I can't get rid of it.

Sorry Lewis I don't understand this post. You agree that we should not focus on one run and unfairly chastise the senior posters and forecasters for doing so and then state This run looks fantastic for us up North. ????????????????

Yes it did snow - there was fresh snow/slush lying on the roads and cars.

Merry Christmas Everybody, High Chris, The spread is because of variations in the timing, position and angle of the LP with its elongated trough at the beginning of next week. This was also apparent in all the ensembles for yesterday - I am not quite sure why you think it was progged to be cold by all ensemble members. There was quite a lot of discussion about this on here yesterday. Current MetO forecast is for the ppn to start as rain and then change to snow.

no one seems to have mentioned the 120 fax Shows the low and front in the correct positions (for a battleground) but 528Dam is too far North - this looks like rain except on hills. Should turn to snow when the low moves through but I am not sure how much.

quite

No I wasn't because meteociel do not do one for Aberdeen. This is the one for Perth -a cold and a mild outlier! There was a similar one for Northampton earlier

And a Merry Christmas to you as well - we have all enjoyed your posts - there is nothing like a good ramp even though we always get told off for it.

Thanks - I hope some people read it (including snowlover2009) - not a good time to be posting.

Yes you are probably right about the too much fussing out at that timescale but the model output is so interesting it is fascinating to ponder over how it will evolve.

there is something wrong with the Netweather ensembles - this happened earlier. Here is the ensemble for London - no outlier but still the mild blip un til this resolved - fantastic control run again