Model Output Discussion - 23rd Jan - 12z onwards

[Cloud 10]

Please excuse my ignorance but the last cold spell (or day) got slowly shunted west with every run will this do the same and move east and end in zero again ?

 

The probable cold spell coming up has a much greater margin for error than the last one,thanks to a "spoke" of the polar vortex setting up shop over Scandinavia.

 

 

 

Compare this to last weeks cold spell which had a very narrow margin of error.

 

[BLAST FROM THE PAST]

I wonder what I F will come to the table with next time we hear from him?   Bet its very interesting 

 

BFTP

[Nouska]

as the ecm mean dribbles out, i notice that at day 5, the dam of the low over ne scotland is 498 !!!  now i know we have to take slp into account to derive the actual thickness but when was the last time a system with such a low raw dam was over the uk?

 

Yes, Nick - quite a difference in thickness between ECM and GFS at the 120 mark. Am I reading that ECM chart correctly - the whole of the UK is sub 510?

 

[BLAST FROM THE PAST]

The probable cold spell coming up has a much greater margin for error than the last one,thanks to a "spoke" of the polar vortex setting up shop over Scandinavia.

 

ECH1-168.gif

 

 

Compare this to last weeks cold spell which had a very narrow margin of error.

 

ECH1-0.gif

Excellent post and spot

 

 

BFTP

[MR EXTREMES]

ECM....garden path...no blocking...moderated uppers closer to the time...chance of slipping east at last minute....Welcome to Winter 14/15 on NW. 

 

Charts look quite exciting tonight, but until they come anywhere close to T72 and show signs of holding true or improving/upgrading at that range, then they are just a computerised solution that is starting to come together and bring a vauge level of consistency. That's the way it shall be until T72 and that's the way ALL should approach the charts, mild, cold, snowy, windy, stormy, wet..etc. 

 

Let's hope we are onto something, but at the moment - no expectations, no dissapointment.

Did you see the ukmo at 144 and ecm at 144 and gfs at 144 they all look rather tasty ecm and ukmo the best of the 3 but be interesting to see what the jma is looking like.

But the shift East would be just our luck but then there's a ridge into Russia and eastern Scandinavia preventing the low to go to Far East.

I'd be inclined to think of anything we could see a shift west seems to be as common as shifts East

[PHLIPPY67]

So the Models/Charst are showing another severe cold spell coming...as the last 2 went from perfect to pitiful...for most of us..a few days beforehand, i'll wait until they arive before i am convinced this time...

[bluearmy]

BA what do you make of the spread to the nw at T240hrs. The 850's spreads look to me to confirm that as high pressure.

 

it does look that way nick. the extended eps delay the split breakdown yet another 24 hours from yesterdays run. if the states stay amplified for longer, we may get a cut off feature into the greenland locale. the suite does flatten the atlantic as the usa trough lifts out towards baffin and meets the siberian chunk headed that way. interestingly, if you have faith in the run, it ends with another build of mid atlantic heights.

 

just watched joe B's staurday summary (i think its free to watch on a sunday on weatherbell). might be worth a watch. his thoughts for weeks 3 and 4 are, i think, in line with the ec 32 which builds anomolous heights over the top of the pole and generates a -AO with a general polar HLB.  any breakdown of the cold might be shorter than the one we see sun through wed this week.

[Frosty.]

So the Models/Charst are showing another severe cold spell coming...as the last 2 went from perfect to pitiful...for most of us..a few days beforehand, i'll wait until they arive before i am convinced this time...

It starts in 4 days, and the others before were nothing like as promising as this one. This one will deliver, unlike the others, I haven't seen such emphatic support for a prolonged wintry spell for a good few years, the south should do much better this time.

[bluearmy]

Yes, Nick - quite a difference in thickness between ECM and GFS at the 120 mark. Am I reading that ECM chart correctly - the whole of the UK is sub 510?

 

 

 

sorry nouska - they look similar to me. actual thicknesses 522-528 dam.  raw is down to 498 ne scotland though slp at 975 mb up there.

[The Post-modern Winter]

 

Not feeling that chart - IDO Pm'd me the 16 day mean for January 14th 1963 and it's showing a strongly westerly flow from a dominant Atlantic

Edited January 24, 2015 by The Post-modern Winter

[Cloud 10]

New fax chart for Thursday is out already and has the 528 dam line well south of the UK with various troughs heading South in a cold Northerly air stream.

 

 

 

[bluearmy]

ECM....garden path...no blocking...moderated uppers closer to the time...chance of slipping east at last minute....Welcome to Winter 14/15 on NW. 

 

Charts look quite exciting tonight, but until they come anywhere close to T72 and show signs of holding true or improving/upgrading at that range, then they are just a computerised solution that is starting to come together and bring a vauge level of consistency. That's the way it shall be until T72 and that's the way ALL should approach the charts, mild, cold, snowy, windy, stormy, wet..etc. 

 

Let's hope we are onto something, but at the moment - no expectations, no dissapointment.

 

shouldn't this be on the moan thread? it doesnt reflect the CONSISTENT output

 

'Much of the UK is likely to be in a cold, showery airstream at first, with sleet and snow showers across northwestern parts of the UK. Gales are likely across northern Britain too. These colder conditions are expected to last through Friday and into the weekend, with further spells of snow and overnight frost and ice, especially across the north of the UK.'

 

thats what the metoffice say for thurs onwards. this nonsense that cropped up re charts T72+ being unreliable .......     not sure where its come from. 

Not feeling that chart - IDO Pm'd me the 16 mean for January 14th 1963 and it's showing a strongly westerly flow from a dominant Atlantic

 

Nope - another incorrect statemtent

 

http://www.meteociel.fr/modeles/archives/archives.php?day=14&month=1&hour=0&year=1963&map=4&mode=2

[The Post-modern Winter]

shouldn't this be on the moan thread? it doesnt reflect the CONSISTENT output

 

'Much of the UK is likely to be in a cold, showery airstream at first, with sleet and snow showers across northwestern parts of the UK. Gales are likely across northern Britain too. These colder conditions are expected to last through Friday and into the weekend, with further spells of snow and overnight frost and ice, especially across the north of the UK.'

 

thats what the metoffice say for thurs onwards. this nonsense that cropped up re charts T72+ being unreliable .......     not sure where its come from. 

 

Nope - another incorrect statemtent

 

http://www.meteociel.fr/modeles/archives/archives.php?day=14&month=1&hour=0&year=1963&map=4&mode=2

 

Can you hear that BA?? Wait, Just listen. . I think it's the sound of something going over your head.

 

 

 

 

 

 

I mean seriously, my reference to IDO PM'ing me is an obvious indicator of a little jesting. .

[Nouska]

sorry nouska - they look similar to me. actual thicknesses 522-528 dam.  raw is down to 498 ne scotland though slp at 975 mb up there.

 

What is the 516 line that is down into France?

 

[bluearmy]

Can you hear that BA?? Wait, Just listen. . I think it's the sound of something going over your head.

 

 

 

 

 

 

I mean seriously, my reference to IDO PM'ing me is an obvious indicator of a little jesting. .

 

been a long day!     can you put a little wink or smiley next time !!

 

(i have no idea re your relationship with IDO ) 

[Ali1977]

The BBC long range coming on in a minute should give us a good idea as to what the METO think will happen next week, obviously Thurs/Fri still a little way off though so subject to change. I'd be surprised if Scotland and the North of England are not shown as close to Zero maximums by the weekend.

[bluearmy]

What is the 516 line that is down into France?

 

 

 

thats the raw dam nouska. to find the actual thickness, you need to add the (SLP * 0.88) to the raw and for slp above 1000 mb, add it. 

[Gael_Force]

thats the raw dam nouska. to find the actual thickness, you need to add the (SLP * 0.88) to the raw and for slp above 1000 mb, add it. 

 

Thanks, I understand that but the chart description says that it is the 1000 - 500 thickness as well as the colours for 500 heights. I'm not any more clued up than the person asking the question so clarification is helpful.

Edited January 24, 2015 by Gael_Force

[Ali1977]

The BBC long range coming on in a minute should give us a good idea as to what the METO think will happen next week, obviously Thurs/Fri still a little way off though so subject to change. I'd be surprised if Scotland and the North of England are not shown as close to Zero maximums by the weekend.

Never elaborated on much past Thurs, good idea I guess...around 5-6c with a decent windchill by then though, blizzards in Scottish hills.

[bluearmy]

Thanks, I understand that but the chart description says that it is the 1000 - 500 thickness as well as the colours for 500 heights. I'm not any more clued up than the person asking the question so clarification is helpful.

 

thankfully, we dont live at 500mb gael.  thickness up there will be very low but you need to use the slp to calc the surface thickness

[Nouska]

thats the raw dam nouska. to find the actual thickness, you need to add the (SLP * 0.88) to the raw and for slp above 1000 mb, add it. 

 

I've finally found the right thickness charts where the calculation is done for the dummy.

http://brunnur.vedur.is/kort/ecm0125/2015/01/24/12/ecm0125_nat_msl_thk500_thk500-thk12h_uv700_2015012412_120.png

 

522 on  the coast.

[Eugene]

So the Models/Charst are showing another severe cold spell coming...as the last 2 went from perfect to pitiful...for most of us..a few days beforehand, i'll wait until they arive before i am convinced this time...

 

 

In North America yes, here no, no wonder they let you down when you have such high expectations.

 

Models show modified Arctic Maritime Northerlies, max temps for most of england will be 3C to 6C and 0C to -2C mins maybe lower if winds die down.

[Ali1977]

Never elaborated on much past Thurs, good idea I guess...around 5-6c with a decent windchill by then though, blizzards in Scottish hills.

He did mention gale force winds though, even 5c and those winds give wind chills of -4c ish, that's day time and by Thursday. by the weekend they could be much lower..

[Vorticity0123]

With the first cold spell of 2015 now behind us, a milder interlude appears to be approaching. Interestingly, this interlude might bring some stormy weather on Wednesday or Thursday. Thereafter, the probability of another colder spell seems to be increasing via a potent northerly flow, which is connected to the storm system approaching on Thursday. How significant will this storm system be, and how is it related to a possible cold spell approaching? And what are the long term trends? I’ll try to address these questions in this post.

 

First, the current weather will be discussed. Thereafter, I’ll go into somewhat more detail to the storm system on Thursday. Finally, a brief look toward the weather in the long term will be given.

 

Current situation

 

For the first 5 days, I’ll use the GFS 12Z run as a general guide.

 

We are currently experiencing a moderately amplified pattern. Various weak 500 hPa ridges and troughs can be distinguished, as given below:

 

Surface level pressure and 500 hPa heights (colours) GFS 12Z run, T+0.

 

A series of 500 hPa ridges (orange colours pointing northward; denoted by red curved lines) can be seen over and just to the west of the UK and near Ukraine. The ridge over the UK is accompanied by a surface ridge, bringing calm weather for the UK today.

On the other hand, a 500 hPa trough (blue/green colours edging southward, denoted by blue curved lines) can be seen just to the southeast of Nova Scotia. Over Central Europe, a deeper trough is present, with associated surface low pressure activity (blue-encircled). Looking further poleward, a very deep trough (resembling a piece of the polar vortex; purple colours, blue-encircled) is present just to the west of Greenland.

 

Two days later, the general pattern is still intact, as can be seen in the link below:

 

http://www.wetterzentrale.de/pics/Rtavn481.gif

Surface level pressure and 500 hPa heights (colours) GFS 12Z run, T+48

 

There is one notable difference, though, as the major trough over Greenland has extended its influence somewhat to the south.
 

Storm system

 

Two days later (Wednesday), a significant piece the deep 500 hPa trough near Greenland moves southwest toward the region near Iceland, as shown in the GFS forecast below:

 

Surface level pressure and 500 hPa heights (colours) GFS 12Z run, T+96

 

The trough at 500 hPa (purple colours, black-encircled) is associated with a complex deep low pressure system at the surface. Furthermore, the Azores high has become rather prominent, also being very well-defined at 500 hPa (red-encircled, red colours). This high pressure area also causes weak poleward ridging to be present to the east of Nova Scotia.

 

Thursday appears to be becoming the day where the storm system will be the closest to Western Europe. Therefore, the GFS, UKMET and ECMWF-runs for Thursday 12 UTC are given:

 

http://www.wetterzentrale.de/pics/Recm1201.gif (ECMWF)

http://www.wetterzentrale.de/pics/Rukm1201.gif (UKMET)

http://www.wetterzentrale.de/pics/Rtavn1201.gif (GFS)
 

All three models have a sub-970 hPa low pressure area somewhere between Iceland and Norway. However, a notable fact is that the UKMET is much further east than the ECMWF and the GFS, having the centre directly over southern Norway. This will have effects on the wind field, but also on the temperatures. This has to do with the fact that any further eastward placement of the low will cause winds over the UK to be more from the North than the Northwest, yielding colder conditions.
 

A critical side note is that the winds will be the strongest on Wednesday (35 kt to the east of Ireland). The winds on Wednesday will be less intense, with probably no storm conditions (>35 kt average wind) being experienced at all over the UK. The strongest winds will be located to the west of the UK, all the way down toward southern France. This can be seen here. The cause for this is the fact that the pressure gradient is not that large anywhere over Western Europe.

 

Finally, it is important to realize that there could be some small but very important variations for the forecast of this low pressure area over the next 5 days. This can be emphasized by the GFS ensemble pressure average for next Thursday:

 

Surface level pressure and 500 hPa heights (colours) GFS 12Z Ensemble T+120

 

The average of the GFS ensembles is giving a sub-970 low pressure area at the surface between Scotland and Norway. Such low average pressure for 5 days out is very impressive. If one would take the most extreme calculations (which is meant to only emphasize the potential of the situation), the low pressure area(s) could be modelled probably as low as 950 hPa, with significant implications for the wind experienced over Western Europe.

 

Mid-term forecast

 

After the passage of this storm system, the surface features on the main global models start to diverge significantly. This makes analysing this in detail fruitless. Therefore, I’ll only compare the Ensemble forecasts of the ECMWF and the GFS to explore and compare the general 500 hPa placement of ridges and troughs.

 

Below are the ensemble means of the surface level pressure and 500 hPa heights of the GFS and ECMWF, 7 days out:

 

http://www.wetterzentrale.de/pics/Rz500m7.gif GFS

http://www.wetterzentrale.de/pics/Reem1681.gif ECMWF

 

Both ensembles show a potent trough at 500 hPa (blue colours) over Scandinavia, edging as far south as North Africa. Furthermore, the Azores high appears to be ridging slightly northward toward Greenland (yellow colours edging poleward).

 

However, there seems to be discrepancy between the orientation of the trough between the GFS and the ECMWF. The ECMWF shows a more North-South orientated trough, while the GFS trough is somewhat more Northwest-Southeast orientated. This will have important implications for the general flow over the UK (from the North on the EC and from the Northwest on the GFS). Furthermore, the GFS pattern is slightly less amplified (more east-west running isohypses) than the ECMWF (more north-south running isohypses).

 

Coupling between storm system and cold spell

 

The cold spell denoted above is caused by the storm system and associated 500 hPa trough digging southward into western Europe. This then gives way to northerlies or northwesterlies to develop on the western side of the system.

 

Stratospheric coupling

 

Interestingly, the synoptic pattern described above can also be seen at the 100 hPa-level (being the lower Stratosphere). This can be seen below:

http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/ecmwf100f192.gif ECMWF 100 hPa heights 12 UTC 23 January run, T 196.

Note that this is the ECMWF run of yesterday, but then for 24 hours further ahead (so in short it is the forecast from yesterday of the same time as analysed above).

 

What can be seen is that the ridge to the north of the Azores is also visible at 100 hPa (isohypses/contours edging northward). Furthermore, isohypses can be seen edging southward over Western Europe, indicating the presence of troughing in that region.  This coincides with the trough present at 500 hPa as indicated by the ensemble forecasts. The Polar vortex is located over Siberia.

 

Long-term trends

For the trends of more than 8 days out, I’ll assess the 8-14 day 500 hPa heights and anomalies of NOAA and the “pluim†of the ECMWF for the Netherlands. First, the “pluim†is given.

 

ECMWF temperature ‘pluim’ of the Netherlands, showing surface temperature calculations of 50 members of the ECMWF model, including the operational run (red).

 

As can be seen, after a brief milder interlude up to Thursday, temperatures appear to be dropping below average, barely getting above zero during daytime. If one follows the average (dashed) line, the temperature drops even more (as well as the spread) indicating that more model runs are going for even colder temperatures in about 10 days. Thereafter, a warming trend appears to be becoming visible, but this is too far out to draw any meaningful conclusions about yet.

 

Judging from the NOAA 8-14 day outlook, the same synoptic pattern as described in the mid-term outlook appears to be present:

 

NOAA 8-14 day 500 hPa heights (contours) and anomalies (dashed lines).

 

On average a ridge dominating over the Atlantic, with troughing extending over Western Europe. This can be seen by the 500 hPa heights extending toward the pole over the Atlantic and toward the Equator over Western Europe. Such pattern usually results in some kind of a Northwesterly flow, precluding any return to mild weather.

 

Conclusion

 

We are standing at the beginning of a very interesting week of weather, with a possible storm system on Wednesday/Thursday and maybe a colder spell afterward. The weather won’t disappoint us this week, that is for sure!

 

Sources:

http://www.wetterzentrale.de/topkarten/fsavneur.html

http://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php

http://www.weerplaza.nl/15daagseverwachting/?r=midden&type=eps_pluim

http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/

Edited January 24, 2015 by Vorticity0123

[Continental Climate]

Bit of a kick in the teeth really whilst we are bathed in the heady temps of -4 850's the Yanks in the north east have -24 850's to contend with http://modeles.meteociel.fr/modeles/gfs/runs/2015012418/gfsnh-1-150.png?18!! I for one am not getting my hopes up about this upcoming cold spell. Lots of cold rain i suspect away from the Scottish mountains. 

Edited January 24, 2015 by Continental Climate