FSXX synoptic spiky trough Convergence line

[Jo Farrow]

There was a strange spiky trough line on the MO FSXX this morning in the Channel

https://forum.netweather.tv/gallery/image/20918-fsxx-5th-feb-2015/

 

 

A black line like the usual troughs but with fins. 

Does this show an upper trough, from a mature/decaying warm front, occluding

Trowal maybe a Canadian term http://tornado.sfsu.edu/geosciences/classes/m500/labs/Lab4_Spring2012/Lab4_Key.html

[Nick L]

There was a strange spiky trough line on the MO FSXX this morning in the Channel

 

 

 

A black line like the usual troughs but with fins. 

Does this show an upper trough, from a mature/decaying warm front, occluding

Trowal maybe a Canadian term http://tornado.sfsu.edu/geosciences/classes/m500/labs/Lab4_Spring2012/Lab4_Key.html

 

I thought they represented convergence lines? 

[Nick F]

Yes, as Nick L says, I thought these mark a convergence zone?

[Nick F]

Scroll to the very bottom of this page and it shows them:

 

http://www.metoffice.gov.uk/guide/weather/symbols

[Jo Farrow]

So a surface feature only

https://forum.netweather.tv/gallery/image/20919-fsxxconverg/

tonight's surface winds in the Channel, the line is there

[Jo Farrow]

And there's the real data in the Channel, snow on Peninsula of Normandy NW of Bayeux. So although position of  trough lines aren't to be taken too literally on synoptic charts, this convergence line was a fine bit of info.

https://forum.netweather.tv/gallery/image/20920-fsxxfrance/

[Vorticity0123]

 

So a surface feature only

 

It first needs to be emphasized that I am by no means an expert om this subject, but I hope I can add a little to this discussion.

 

Surface signature

 

On the WRF forecast of 20:00 local time (12Z run) the line of convergence (winds blowing toward each other) can be identified over the extreme southeast of the UK extending toward northwestern France, as given by the black line:

 

WRF 10 meter winds (12Z, T+7h).

 

500 hPa signature

 

If one checks the 500 hPa charts, there does not seem to be any evidence of the convergence line at that level. However, on further analysis, there could be something in the way of convergence visible, or even a trough, as given below:

 

WRF 500 hPa heights (colours) and surface level pressure (12Z T+7h)

 

The blue arrows on the image show 'lines' of equal pressure at the 500 hPa level. Basically, they can be interpreted as flowlines at 500 hPa; the air would by approximation flow along these lines. The position of the surface convergence zone is approximately located at the black line on the same image. The red line shows the axis of a 500 hPa trough present over the area.

 

Theory 1

 

At the bigger picture, it can be seen that lower heights at 500 hPa (about equal to lower pressure at 500 hPa) are edging northward from the southwest of France toward the UK (its axis is denoted by the red line). This indicates the presence of a 500 hPa trough being positioned there. This trough does quite well overlap with the surface convergence zone, though its position of the 500 hPa trough axis is located to the east of the surface feature.

 

Theory 2

 

Another theory is that if one follows the flow around this trough at 500 hPa (blue arrows), one can see them converging almost atop of the surface convergence zone. This means that the surface convergence zone could well be identified at 500 hPa as a convergence zone.

 

What do you think about this analysis?

 

Sources:

http://www.meteociel.fr/modeles/wrfnmm.php?ech=3&mode=2&map=300

[Midlands Ice Age]

I am interested in this topic, because I have just looked at the Netweather RADAR, and it is showing a similar set up for a line of convergence currently happening but much further to the north. When I saw the title of this thread I thought someone else may have noticed it too. Hence my post on here....

During the day it has steadily crossed the country in an effective general WNW direction. Although the rainfall is moving along the line in an a WSW direction.

The rainfall line currently lies from Newcastle to Liverpool and down thru Wales to the South West Of England. To me it looks as though it will move thru most of Ireland before it stops moving northwest

I believe it seems as though it is moving much more North and West than forecast.

Is this significant in terms of the development of the high over the next few hours? Could it be that the high will get pushed further north and west? (One can hope!!)

I am very surprised it has got this far north, as behind it the wind is swinging to a more Easterly direction and there is an effective boundary being formed by the continental air being forced WNW from the near continent and Denmark.

Perhaps it is more in hope than expectation so can anyone comment?

MIA

[Jo Farrow]

I am interested in this topic, because I have just looked at the Netweather RADAR, and it is showing a similar set up for a line of convergence currently happening but much further to the north. When I saw the title of this thread I thought someone else may have noticed it too. Hence my post on here....

During the day it has steadily crossed the country in an effective general WNW direction. Although the rainfall is moving along the line in an a WSW direction.

The rainfall line currently lies from Newcastle to Liverpool and down thru Wales to the South West Of England. To me it looks as though it will move thru most of Ireland before it stops moving northwest

I believe it seems as though it is moving much more North and West than forecast.

Is this significant in terms of the development of the high over the next few hours? Could it be that the high will get pushed further north and west? (One can hope!!)

I am very surprised it has got this far north, as behind it the wind is swinging to a more Easterly direction and there is an effective boundary being formed by the continental air being forced WNW from the near continent and Denmark.

Perhaps it is more in hope than expectation so can anyone comment?

MIA

I think the more northern line you mention links to an occlusion, so the prec is from that frontal weakness. The MO synoptic charts do show a cold front appearing with that continental air spiling into the SE. The Occlusion and the cold front  seem to merge on their charts anyway

[Midlands Ice Age]

 

I think the more northern line you mention links to an occlusion, so the prec is from that frontal weakness. The MO synoptic charts do show a cold front appearing with that continental air spiling into the SE. The Occlusion and the cold front  seem to merge on their charts anyway

Joe,

Thanks for your response, I am sure it is some sort of occlusion. it is how far north and west it is getting which is of interest to me. Didn't think the charts showed the one in the south east would get anywhere near this far north at least bty this time.

MIA