25 replies to this topic

[staplehurst]

Harry, on 21 August 2011 - 17:23 , said:

Haha, yay to me

I was watching it veer sharply towards the East and questioned whether you would ever see such ludicrous changes in direction elsewhere in the world - only a storm on course for our shores could be knocked away so easily...sometimes MCS' due to their scale will move more independently of veering/steering winds and plough on through...one example of that was a couple of years ago where the general flow was from a SSW to the NNE...an MCS was forecast to run up from France, possibly clipping Kent en route...woke the following day to see it had veered towards the NW and clattered into Cornwall/Devon causing immense frustration as it scuppered convective potential for that day.

Alas...here we are still waiting for a proper import to reach the south coast this year...almost all have stayed in the channel or veered east towards Benelux.

On the plus side, and it's limited enthusiasm I have to say, the thundery low forecast to move up Monday night is not showing much sign of shunting eastwards...in fact, subtle changes are pushing it ever so slightly westwards...if we want to see proper thunderstorm weather we need to be on the eastern side of that low as much as possible...western or northern edge and it'll be frontal mess.

Still can't call it

25th May 2009 - ask Dogs32/Pat/(whatever name he has now haha).

Significance of upper frontal feature really just brings a change of airmass in the upper levels of the atmosphere rather than at the surface. As a result, you may have noticed many of the fronts recently have had rain not only falling from mid-high level cloud (rather than low cloud), but also a significant distance away from the actual surface front (take Thursday for example, huge mass of rain over CS Eng and S Midlands, yet the actual front was over the Channel closest to France).

EDIT: Notice on the current T+48 a warm front ahead of the main frontal system, this will no doubt be an upper level feature, and by T+60 it's drawn as an upper occlusion. Something's certainly out of the ordinary with our summer weather this year!

Edited by staplehurst, 21 August 2011 - 18:08 .

[Harry]

Just seen the new FAX chart which does make the risk of storm cells far less likely...the centre of the low though is slightly further West which is far better than being further East...whether we can hope/expect embedded thunderstorms within the frontal zones I don't know...but what we do have is a pretty vigorous triple point which do have a reputation of bringing more intense prolonged rainfall.

I would like to ask a question though to the more knowledgeable and experienced chaps...can MCS' type features exist amongst frontal zones?

Traditionally in the UK MCS features are not associated with fronts but with more subtle atmospheric disturbances...given the presence of the trough over France with very high CAPE/instability, thunderstorms are almost certainly going to develop here and drift north/north east with the low pressure system...could an MCS develop along the fronts or is that neither possible or likely? Anything convective that does develop I would suspect is liable to bear supercellular characteristics and turn possibly tornadic at times given the shear likely to be present.

Noticed that the first few storms are starting to fire over Benelux, bit later than I was expecting.

Edited by Harry, 21 August 2011 - 19:16 .

[Nick F]

Certainly wouldn't rule out some thundery activity Monday night and through Tuesday across parts of England and Wales, as the thundery low currently across Iberia tracks N across the Bay of Biscay and reaches south coast of England on Tuesday morning. Rather warm moist air aloft drifts north across England and Wales by Tuesday morning, as shown by the theta-w (wet bulb potential charts):



When you've got this amount of warm moist air in the atmosphere, a low with a triple point moving over - you can't rule out thunderstorms - even if GFS shows no CAPE. I don't think the models (i.e. GFS) handle storms too well in these plume type set-ups.

Lots of storms across iberia this evening looking at the sferic plots and sat pics (below), some cold cloud tops looking at spectral too, showing these storms are pretty strong in places. Be interesting see how the models handle this thundery low moving north over the next 36-48 hours.



Been plenty of let downs from similar set-ups in recent years, but there is always the unexpected when thinking that nothing is likely looking at GFS CAPE charts, last night was a good example when storms broke out across parts of England and Wales, despite GFS seeming rather uninterested in the idea.

[Victor Meldrew]

After all the mention of a storm I think i'll give up, what a terrible few years. However by that we've had some fantastic winters!

[Harry]

Nick F, on 21 August 2011 - 19:53 , said:

Certainly wouldn't rule out some thundery activity Monday night and through Tuesday across parts of England and Wales, as the thundery low currently across Iberia tracks N across the Bay of Biscay and reaches south coast of England on Tuesday morning. Rather warm moist air aloft drifts north across England and Wales by Tuesday morning, as shown by the theta-w (wet bulb potential charts):

gfs_the700_eur36.png gfs_the700_eur42.png

When you've got this amount of warm moist air in the atmosphere, a low with a triple point moving over - you can't rule out thunderstorms - even if GFS shows no CAPE. I don't think the models (i.e. GFS) handle storms too well in these plume type set-ups.

Lots of storms across iberia this evening looking at the sferic plots and sat pics (below), some cold cloud tops looking at spectral too, showing these storms are pretty strong in places. Be interesting see how the models handle this thundery low moving north over the next 36-48 hours.

IR_108.jpg IR_108ctt.jpg

Been plenty of let downs from similar set-ups in recent years, but there is always the unexpected when thinking that nothing is likely looking at GFS CAPE charts, last night was a good example when storms broke out across parts of England and Wales, despite GFS seeming rather uninterested in the idea.

Wow cheers Nick....stunned by some of the cloud tops over Spain - circa -65C!!!

Fingers crossed!! I notice as ever estofex seemingly taking their time...it appears they like GFS struggle a wee bit with the dynamics of these setups!!

[Stormmad26]

If there's one night and morning for at least the last 2 months or year when I don't want heavy rain or thunderstorms and wouldn't be able to stay up and watch them, it's Monday night into Tuesday! I just knew the charts several days ago would shunt this weekend's possible plume eastwards, while upgrading Monday night into Tuesday.. looks like I was right.

Therefore, expect thunderstorms, especially in East Devon!