nick sussex

The same old failings seen during the winter are appearing yet again with the models. Initial amplified patterns shown in later timeframes become flatter as these head towards the 144hrs timeframe. Overall the models have downgraded the wintry potential this evening and both the GFS and ECM make hard work of ejecting the low south at 168hrs, the ECM hardly manages this before the next low moves in , the ECM produces a much better looking Scandi high with better cold to be advected west but the Atlantic rolls in and keeps this to the east. It shows just how difficult it is to get a low dropping south with ridge backing west over the top to verify. Although the outlook does look somewhat colder it's hard to see a real taste of winter occuring off tonights operational output. Unless you're on top of a mountain it just looks cold and wet on the ECM, its morning output was far better, if we don't get a westwards correction in the output tomorrow and a weaker looking Atlantic then I think thats game over in terms of chances for some lower ground snow that can last and not disappear by lunch time.

Looking at the overall output it looks like it will be turn somewhat colder towards the weekend with high pressure to the ne and the Azores high displacing nw into the Atlantic. http://www.ecmwf.int/samples/d/inspect/catalog/samplers/banner/mean_sea_level_pressure_and_temperature_at_850hpa!168!pop!od!enfo!enplot!2009112700!!/ If you look at the ECM ensemble maps still alot of variation however with what happens to low pressure near the UK and we're not certain to get that low to head south into France, or whether the outlook would be more in line with the GFS 06hrs which doesn't sink the troughing but takes some energy north clearing the path for that Channel Low. For this reason prospects in relation to snow are way too far out to have any confidence in. It's a case of interesting synoptics but late in the season and marginality is going to be a problem. Of course the continent has warmed significantly and it will need a decent injection of cold uppers on the GFS 06hrs there to be advected west to deliver for the UK and even though the GFS progs snow off the northern flank of that Channel low I'm not convinced. The ECM would take longer to develop any snow chances but has a better ridge to the east and low pressure looks like it could be forced se through the UK later, again though what that produces is hard to say as we just don't know how much cold will be available at the time. I think for the timebeing we just need to see the pattern remain sufficiently amplified upstream to force the removal of the limpet high to the south, and force heights to drop in central Europe.

Yes the infamous GFS 850's predictions! I think the ones upto 240hrs look okay but the ones right at the end of FI look a bit far fetched! Certainly the GFS overdoes the southwards extent of cold when theres no proper Greenland high, so that ties in with your thoughts regarding December 2010, with the rare Greenland high visitor you've got several days to get the cold uppers down. I think it would need a lot of good fortune to just get the first low dropping south with ridge backing west within 240hrs.

Very quiet in here considering both the ECM and GFS evenings outputs are the best we've seen for many weeks for cold and wintry potential. It's probably understandable though that people are somewhat model fatigued after an overall very disappointing winter. In terms of the trend to drop low pressure south with ridge backing west over the top, it's not a pattern that happens all that much and its quite complicated hence it's still quite a hurdle to overcome. Some uncertainty with how much cold will be available to tap into and whether this could produce a rain to snow event if it managed to verify. In terms of the ECM ensemble maps, some interesting options at 168hrs: http://www.ecmwf.int/samples/d/inspect/catalog/samplers/banner/mean_sea_level_pressure_and_temperature_at_850hpa!168!pop!od!enfo!enplot!2009112700!!/ If the trend is maintained tomorrow then perhaps we can look forward to something colder with even chances for some snow for favoured areas but given the winter best to keep expectations low until we see that low drop south within a closer modelling timeframe.

I'd agree with this, yesterday evenings 12hrs ECM run was a much better route forward for some interesting weather, not desperately cold but you'd get some wintry showers and eventually some snow with good convection and some alleviation of the drought for southern areas. It's hard to see a northerly occuring even with the ECM but a ne flow could have moved in as the troughing sunk into Europe, high pressure over Scandi but orientated unfavourably to deliver real cold to the UK would just eat up any remaining chances for cold and wintry conditions for the UK.

Really to alleviate the drought conditions in southern areas we need to see the Azores high displaced, aswell as this for those looking for some late season snow and cold that needs to take a hike! Certainly the longer range ECM De Bilt ensembles have improved regarding colder prospects: http://www.weerplaza.nl/15daagseverwachting/default.asp?type=eps_pluim Bearing in mind that troughing sinking into Europe would likely provide especially northern areas of the UK with colder temps than Holland which may take longer to get on the cold side of any troughing.

At last some signs of a change in the pattern but still too far out to assume the Azores high will be displaced into the mid Atlantic. The ECM does follow its morning trend, the UKMO again wants to bring a stronger ridge into play but you suspect this won't last long as troughing to the west edges east, the GFS is less bullish regarding the removal of the limpet high. Looking at the ECM ensemble maps these are supportive of troughing near the UK at 168hrs, this is likely to verify but its the orientation of this and what happens to high pressure to the south thats still undecided. http://www.ecmwf.int/samples/d/inspect/catalog/samplers/banner/mean_sea_level_pressure_and_temperature_at_850hpa!168!pop!od!enfo!enplot!2009112700!!/ It's clear to see from those ensemble maps which members could go on to provide a change to more unsettled and colder conditions and which suggest a flatter upstream pattern with the limpet high still proving a difficult obstacle to overcome.

If these height rises do occur to the ne then this should at least force the jet on a more nw/se trajectory into the UK and does open the door for some colder conditions. The key area as always in this type of set up is the area around Svalbard , the ECM does raise pressure there at 192hrs, still too far out to be sure this is going to happen but that would be the first stage in a change of pattern. We'll just have to see whether this trend is built on over the next few runs.

These two links give the AO and NAO monthly readings back to 1950: http://www.esrl.noaa.gov/psd/data/correlation/ao.data http://www.esrl.noaa.gov/psd/data/correlation/nao.data I'm not sure about data before that period, maybe someone else has a link to before that.

More concrete signs today that high pressure will be edged further north with time and better agreement on some mid Atlantic troughing at 144hrs. The PV which was shown very strong just a few days ago has been toned down with some fragmenting of this and the NH pattern seems to look a little better for those looking for some colder weather during March. Still hard to see this coming from the north and it looks like we'd have to be looking to the ne or east for a change and that again depends on whether any cold pooling can be advected west, we've seen just how difficult this is with the northern arm of the jet often throwing a spanner in the works.

The last FI ECM tease was a few days back with the suggestion of a possible easterly, that imploded after two runs, tonights doesn't deliver anything within 240hrs but holds a little interest as to where the pattern could go after that.

Perhaps a few hints this evening of some changes in the NH pattern as we head into March, signs of the jet tracking a little further south and a stretching and eventually fragmenting of the PV. The ECM looks to develop a more amplified troughing to the west of the UK at 192hrs, the more digging south of this trough the better chance that as this pivots it ejects some energy se'wards towards Iberia allowing some pressure rises to the ne. Any interest doesn't really appear till the post FI timeframe and the ECM has pulled out the odd interesting run over the last week which its dropped after a day so we'll just have to see whether this is just a one off.

The GFS operational runs seem much more bullish regarding more amplified mid Atlantic troughing which helps to ridge high pressure further ne. They certainly seem more inline with the NOAA maps, the ECM has a flatter pattern and keeps wanting to place troughing much nearer the UK in FI, so this disagreement makes it difficult to decide whether the outlook will trend colder or remain average to above average.

In terms of the GFS 06 hrs run, it continues the same theme of the 00hrs with that troughing in the mid Atlantic forcing high pressure to ridge further north but as TWS mentioned what might look like good synoptics in the middle of winter don't have the same bite in March, if you're going to get a Scandi high at this time of year you need a good cold pool to tap into and in these situations need a piece of the PV to head south into western Russia so that the deeper cold can get advected west on the southern flank of the high. The ECM operational runs are reluctant to develop enough amplification in any mid Atlantic troughing to allow the ridge further north and ne. Looking at the ECM ensemble mean it does look less progressive than the operational output and so some of the ensemble members probably do ridge high pressure further north but really even the GFS would need a much more digging trough further west and more amplification. I would say though that given the reluctance of the PV to leave the Greenland area that the only way out of the current milder pattern would have to come from high pressure ridging north, I can't see any other possible route to colder conditions at the moment and we'd need alot of help from troughing in the Atlantic.

Yes but as you head into March the best source of wintry weather is from the north or ne, easterlies at that point unless in conjunction with a piece of the PV dropping into western Russia lose their bite. The Feb cold spell had some energy going into Iberia and the Med to support the high and also the the lower heights stayed further to the nw.

The ECM 12hrs operational output firmly shuts the door on even a hint of a change suggested by its two previous runs. Gone is the mid Atlantic troughing which may have helped push the ridge further north to be replaced by even deeper low heights to the north, really its output this evening wouldn't look out of place in early winter, strong flat jet, low heights to the north and high pressure to the south. If you're looking for even a chance of some colder conditions the ECM output is a horror show of epic proportions, indeed save for a deep FI tease by the GFS its shocking all round. No appreciable rain for those areas that need it, although one does wonder what will happen when the PV eventually leaves its Greenland home. Once the NAO does eventually go negative I fear it might stay that way for some time! Overall then winter looks to go out as it came in, what happens in March hard to say but if those low heights are maintained to the north then it's hard to see where any cold could come from.

Generally the models all agree on a continuation of low heights to the north and high pressure to the south or se. The GFS 06 hrs run takes the high a little further north than the previous 00hrs, the ECM still suggests that troughing will become established in the mid Atlantic and in terms of looking for any chances for some colder snaps in March that would need to occur to give a chance for high pressure near the UK to ridge further north. It's hard to see how any cold can come from anywhere but the east or ne given the HN pattern and the reluctance of heights to rise near Greenland. In terms of the ECM ensemble maps there are more colder solutions this morning at 168hrs than on yesterday evenings, I'd say theres 10 out of the 50 but this would need a big change in the operational output and by and large the models have been solidly behind flattening the jet out at that timeframe. http://www.ecmwf.int/samples/d/inspect/catalog/samplers/banner/mean_sea_level_pressure_and_temperature_at_850hpa!168!pop!od!enfo!enplot!2012022100!!/

Big differences on the GFS 18hrs run from very early on between the handling of the eastern USA low, the earlier 12hrs run developed this into a much deeper feature much further upstream.

I think we can see where those two diverging opinions are coming from, one the troughing is probably too close and positively tilted driving a mild southerly flow up and the other probably a more amplified neutral/negatively tilted trough further west allowing the ridge to extend far enough north to advect some colder air west on the southern flank.

Yes that CPC chart is certainly giving some support to the ECM operational run tonight, what do you make of the ECM spreads, the 240hrs looks to me to suggest a strongish signal for troughing to the west and a weaker signal for higher pressure to the east. http://www.meteociel.fr/modeles/ecmwf.php?ech=240&mode=1&map=1&type=2

Tonights NOAA maps suggest high pressure is likely to become the main feature in the medium term: http://www.cpc.ncep.noaa.gov/products/predictions/610day/610day.03.gif http://www.cpc.ncep.noaa.gov/products/predictions/814day/814day.03.gif You can see there the trend to edge this further north with lower heights developing in the mid Atlantic. The uncertainty is more in relation to how far north any high ridges and whether troughing in the Atlantic will amplify sufficiently to go that next step in allowing a colder east to ne flow to become established across the UK.

If by some miracle the ECM had the right trend and continued with this over the next few days we'd need to be able to tap into a decent cold pool for it to deliver. Generally I'd prefer to see a more ne flow at this time of year sourced in the Arctic rather than eastern Europe unless that is we can get a piece of the PV to drop south into western Russia.

Dave have you seen the JMA this evening? That will put a smile on your face! I agree the lack of rainfall is a concern but I'm sure the Azores high will leave just in time for summer!

Lol! I can't I'm the one that answers the calls normally! Apologies for my rather sarcastic attitude to the models this evening, putting aside much of the operational output theres one very good chart at 240hrs from the ECM, I'd like to see the troughing at least neutrally or preferably negatively tilted, if that was the case you'd have a very good chance of seeing an easterly or ne flow a few days after. If that was shown within 144hrs I'd be quite positive as it is its at the far reaches of the ECM and hence could well just be a charitable effort by the ECM this evening!

ZZZZZZZ! Thats my thoughts regarding the ECM upto 192hrs, the amplified eastern USA trough flattens out and delivers a level of boredom in tune with most of the winter so far! The GFS continues to make an effort at trying to spur my cognitive function into life but fails as the northern arm of the jet flattens the high out, the UKMO looks similar to the ECM although it takes longer to develop that eastern USA low. Either way it looks a very mundane picture with limpet high to the south and weak low pressure to the north, drab uneventful apart from highish temps this week, hopefully the ECM ensembles have some options that don't induce sleep! A sudden burst of excitement at 216hrs as that troughing digs further south into the Atlantic! At 240hrs the ECM finally decides to bring some interest with the classic pre easterly signature of digging trough in the mid Atlantic and pressure would rise to the east , shame its at 240hrs, no doubt that will implode by tomorrow!