Modelbespreking & visie

Bericht van: sebastiaan (bussum) , 05-02-2011 20:45 

Handige uiteenzetting voor wie vanavond niet alle modellen heeft gezien. Wel Engelstalig en gericht op de UK. Daaronder nog een aardige uiteenzetting.
Voor wie het wil lezen op de oorspronkelijk pagina, zie link helemaal onderaan, wel zo gemakkelijk met de vele 'links' in de tekst.
Here is the review of the extended 12z data taken from the 12z output of UKMO, GFS and ECM for Saturday 5th February.

HEADLINE: Continuing rather unsettled with rain at times. Slowly becoming less mild
UKMO at 144hrs shows a small area of high pressure off western Norway with a deep Atlantic low pressure system south of Greenland. Troughs lie from its centre down through the Atlantic and across the UK with a band of rain running east over all parts with a SW flow following on. Temperatures would be near normal generally but there could be rather colder conditions towards the far east and northeast.

http://www.wzkarten3.de/pics/Rukm1441.gif

GFS at 144hrs is quite similar to UKMO at the same time span with naturally the same weather pattern too but by 168hrs an active Atlantic trough lies close to the west of Britain with heavy rain on its eastern flank edging slowly east. Further east and north things could be drier and somewhat colder in a brisk south or southeast wind. The following day maintains falling pressure over the UK with an intense Low four to five hundred miles west of Ireland at 945mbs. Strong south to southwest winds would drive troughs NE towards and over the UK with wind and rain in abundance with temperatures near normal.

http://www.wzkarten3.de/pics/Rtavn1441.png

http://www.wzkarten3.de/pics/Rtavn1681.png

http://www.wzkarten3.de/pics/Rtavn1921.png

By 216hrs the low has moved to a position between Scotland and Iceland with an active cold front sweeping east through the UK. Rain and very squally winds would rush east over the UK followed by brighter more showery and less windy conditions later. The following day continues a showery theme but a weak ridge would bring a damping down of the showers through the day ahead of the next spell of wind and rain brewing in the Atlantic. This duly arrives at 264hrs with another spell of gales and heavy squally rain sweeping east through all parts followed by colder and more showery conditions from the west later.

http://www.wzkarten3.de/pics/Rtavn2161.png

http://www.wzkarten3.de/pics/Rtavn2401.png

http://www.wzkarten3.de/pics/Rtavn2641.png

After 12hrs or so of squally, heavy and possibly thundery showers rising pressure from the south would see these lessen in frequency and intensity by 288hrs as another weak ridge crosses through. The ridge then collapses away east as winds back SW with a warm front bringing a period of rain and drizzle followed by mild and dank conditions with breezy SW winds and hill mist and drizzle on hills and coasts facing south and west.

http://www.wzkarten3.de/pics/Rtavn2881.png

http://www.wzkarten3.de/pics/Rtavn3121.png

The end of the run shows a couple of milder days before an active trough around 360hrs brings a spell of rain through followed by colder clearer weather later. The final day shows pressure having risen quickly over all parts with a high pressure belt developing over the UK stretching from the SW to the NE. The weather on this day would be dry and chilly after early frost melts away.

http://www.wzkarten3.de/pics/Rtavn3361.png

http://www.wzkarten3.de/pics/Rtavn3601.png

http://www.wzkarten3.de/pics/Rtavn3841.png

GFS ENSEMBLES: The ensembles tonight show that a period of mobility continues with the trend for depressions to bring cooler conditions in the mix for all areas from northern parts of the Atlantic with time. There is little support for anything other than an Atlantic dominance with the mean for the run being quite close to the long term average. There are just a few runs which drift down into the freezer for London at the end including the control but the vast majority maintain a zonal feel about things. As far as Aberdeen is concerned it looks a generally flat pattern with zonality continuing more or less throughout leaving aside the few cold outliers.

http://www.wetterzentrale.de/pics/MT8_London_ens.png

http://www.wetterzentrale.de/pics/MT8_Aberdeen_ens.png

ECM at 144hrs shows high pressure between Iceland and Norway with an intense depression south of Greenland. The UK lies in a moderate southerly flow with a trough moving northwards over England with a band of cloud and rain. Following the rain things would warm up a little following a rather cold start to the day. The next day sees further fronts approaching the SW with the rain chiefly in the west with the east being drier and somewhat colder. By 192hrs pressure is low to the south and west of Britain with various troughs scattered over the nation. High pressure remains to the NE over Scandinavia. While the southwest sees the heaviest rain and the highest temperatures it is likely that areas in the north and east stay drier and become rather cold.

http://www.wzkarten3.de/pics/Recm1441.gif

http://www.wzkarten3.de/pics/Recm1681.gif

http://www.wzkarten3.de/pics/Recm1921.gif

By 216hrs Low pressure dominates the areas from Greenland, through the Atlantic to Britain and south through France and the Med. The weather would be very unsettled and often wet with spells of heavy rain. Away from the far NE where it would be quite windy winds would be mostly light. It would also be rather cold as well with some snow possible on higher ground further north and east. The run ends with active low pressure’s stretching from southern England west through the Atlantic. The north would continue rather cold with rain, sleet or snow at times in a strong ESE flow. The south would likely be simply wet with variable winds and normal temperatures.

http://www.wzkarten3.de/pics/Recm2161.gif

http://www.wzkarten3.de/pics/Recm2401.gif

TRENDS The Atlantic continues to influence the UK weather tonight from our mid range models. There still is some high pressure development to the NE but it appears that the models now think the Atlantic will be too strong to restrict anything other than a continuation of normality with regard to temperatures for us here in the UK. ECM does show the effect of the high pressure to the NE allowing south-eastward moving depressions west of Britain to eventually deliver some rather cold conditions and on reflection it wouldn’t take too much shift in pressure patterns at this time to show something much more promising for widespread cold. However, it looks like we’re going to have to wait for the next set of runs to see what develops or not.

Uiteenzetting
Following on from my positive view of things in the model discussion regarding this mornings output I remain positive this evening regarding the outlook.

Putting aside what the teleconnections suggest for the future lets just deal with the outputs themselves and just deal with the 168hrs timeframe as thats really where the foundations will be set for cold or conversely where it will implode.

What we have at the moment is a signal to develop some pressure rises to the ne, at the same time we have a strong PV desperate to push low pressure east into the UK and its where the battleground sets up thats incredibly difficult to forecast accurately at this timeframe.

The UKMO and ECM agree at 144hrs by keeping the developing high near Scandi far enough north to force the troughing in the west to align nw/se, as soon as this happens and as long as the high holds far enough north pressure will be exerted on the troughing to disrupt. You can see that in these two ECM outputs.

http://www.wetterzentrale.de/pics/Recm1441.html
In the first one above look at the troughing to the west, it looks pretty mean! and wants to kick the high away.

http://www.wetterzentrale.de/pics/Recm1681.html
Now see how some of the energy of that trough is pulled se'wards, at this point you have the foundations to get some colder conditions into the UK.

As soon as you see this its basically a scoring punch for the high!

After this the ECM has a messy picture but note energy heading towards Iberia, this is a good sign. Thats as far as we should look in terms of detail because it doesn't really matter, the crucial time period to have any chance of something much more interesting is between 144 and 168hrs.

It's really down to the initial formation of the high and whether we get some trough disruption but its crucial that we see the high far enough north to exert that pressure on the troughing and you must see that nw/se alignment.

In terms of the other outputs the GFS really doesn't want to know and this applies to the NOGAPS

The GEM isn't great but better than the GFS and NOGAPS.

In the other camp the ECM/UKMO/GME and BOM all look interesting and give some hope.

It's interesting that its the North American models against the Euros and the Australian model.

Generally and has always been something I've stressed in the model discussion and from past experience its much better to have the ECM/UKMO against the GFS than the ECM/GFS against the UKMO as this latter model is often the one thats refused to go with synoptics that involve high pressure from the ne.

For this reason I remain hopeful this evening, cautiously optimistic would best sum it up.

http://forum.netweather.tv/topic/68358-model-output-discussion/page__st__442  Quote selectie