Convective / Storm Risk Discussion - 23rd July 2013 onwards

[Harry]

Indeed....the problem is NAE is showing us accumulations not the type of rainfall....if the purple zone is an electrified MCS then all good. If it is heavy frontal rain then thoroughly boring!!

Will be interested to see how estofex update their extended forecast later

[A.J]

At this rate, you'll need binoculars in Kent to see anything.

image.jpgimage.jpgimage.jpg

it's interesting to see the variance in model runs bud......NAE hi-res 12z moves things to the east, whereas the image below is from the 06z NMM hi-res has the deluge considerably further west....An interesting 12z NMM run awaits......

 

[AWD]

it's interesting to see the variance in model runs bud......NAE hi-res 12z moves things to the east, whereas the image below is from the 06z NMM hi-res has the deluge considerably further west....An interesting 12z NMM run awaits......

viewimage.pbx.png

That looks much more like the 0z NAE run. For balance, I'll also add this from Ian Fergusson regarding the 12z NAE;

"12Z NAE, with MCS drawn up frm Biscay to SE areas into AM, being classed as outlier and not followed for our forecast expectations tomorrow."

[nitro_deluxe]

Wow! Looks a good one from a relatively untrained eye...maybe heavy rain further out west is perhaps more widespread, with possibly a slightly more narrower but intense area, with added sferics further east?

A complex picture as ever - nightmare for forecasting - good fun for the rest, or at least potentially

[East_England_Stormchaser91]

My mind may be starting to believe we actually may see something marvellous judging by this 12z run that is evolving. The centre of that low is centred slap bang in the Midlands and we actually get an influence off the low countries instead of seeing everything be steered towards them. Surely to god this is too good to be true!!

[Harry]

GFS 12z keen to bring more surface CAPE inland across the far SE.

[nitro_deluxe]

My mind may be starting to believe we actually may see something marvellous judging by this 12z run that is evolving. The centre of that low is centred slap bang in the Midlands and we actually get an influence off the low countries instead of seeing everything be steered towards them. Surely to god this is too good to be true!!

Either way, even behind the main thrust of rain/storms, scattered lively thunderstorms are very possible Sunday then other parts into Monday - whole risk gradually transferring north as time progresses. Bring them on..

[shaky]

Amazing gfs shifts things west and nae takes it east!!what a stupid amount of uncertainty this far out and theres only 24 hours left to the actual event!!put it simple nae suggests naff all apart from rain and the gfs suggests nice lightning storms from midlands eastwards!!

Edit:nae is classed as an outlier according to ian ferguson!!expect things to be further west!!

Edited July 26, 2013 by shaky

[Harry]

Worth noting outliers have proven right in the past

[Tamara]

Interesting.

 

Not as bad for the SE on that animation.

 

Dorset and Somerset look to get wet!

In the circumstances of no escape coming from this I would take that (from my personal pov). However the reality more and more is looking worse than that for my local part of the world with increasing focus seemingly right IMBY

 

The 12z GFS increases the CAPE and lifting index figures for late tomorrow afternoon and early evening for a start...

 

The 12z NAE appears to have the surface low on a further eastward track than previously and the precipitation moves through quicker. But the intensity of it and obvious storm modal structure to it is still very stark despite the slight eastward adjustment further than the GFS

Edited July 26, 2013 by Tamara Road

[Harry]

Also worth noting the MetO precip forecast looks little like any of the others!

[A.J]

That looks much more like the 0z NAE run. For balance, I'll also add this from Ian Fergusson regarding the 12z NAE;"12Z NAE, with MCS drawn up frm Biscay to SE areas into AM, being classed as outlier and not followed for our forecast expectations tomorrow."

do you think Ian's inferring that possible MCS will track further NE into Benelux countries or it's track will be further west than NAE modelling?

 

12z GFS rolling out, shows the higher DLS staying generally across the channel, high PWAT values neat the east coast during the overnight period......some mid level capping in place over the SE quadrant....hmm...some parameters don't look all that favourable for widespread storm activity in CS/SE counties, just lots of rain...however there is decent spread of MLCape over parts of the SE during the night, so who knows at this juncture...

 

here's the 12z GFS precip & MLCape forecasts for tomorrow evening/night

 

 

[Harry]

Cheers ajp! Dymchurch it is then

[AWD]

do you think Ian's inferring that possible MCS will track further NE into Benelux countries or it's track will be further west than NAE modelling?

Ask him! lol.

https://mobile.twitter.com/fergieweather

[Adi F]

If my memory serves me correctly each model run is not an update of the run before but an update of the same run 24 hours before. I believe each run uses different parameters and data hence why each run can look so different from the one before. I.E. the 06z run is and update of the 06z run before it. The 12z run will have different data added to it and will update the 12z run before and so on. 

 

I think I recall john Holmes explaining it to me years ago and he said what data is used on each run. Some runs are better at showing one parameter than another such as precipitation. I also seem to remember a sticky post listing the advantages and disadvantages of each run? 

 

As I say i am trying to go on a failing memory so maybe John or someone else can correct me if I am wrong.

[A.J]

Ask him! lol.

https://mobile.twitter.com/fergieweather

I might look like a right twit.....

[Stuart]

Synopsis:

Several episodes of convective weather are expected on Saturday. A sharp Atlantic upper trough will pivot towards Iberia through the day, allowing a very warm, moist plume to be advected northeastwards across much of Western Europe, grazing parts of SE Britain. A series of shortwave troughs in the southwesterly flow will allow scattered severe thunderstorms to develop across France, Germany and the BeNeLux countries, capable of producing very large hail and a few tornadoes. At the surface, a straddling warm front will lie across the Bay of Biscay at the beginning of the forecast period, with cyclogenesis occurring as a developing frontal wave migrates northwards towards and across S/SE Britain.

 

Discussion:

... SHETLAND ...

A post-frontal shortwave trough continues to provide the focus for thunderstorms over the North Sea, moving across Shetland between 00z-06z. Severe weather will be limited by the elevated nature of such thunderstorms, but some small hail is possible in any stronger cores. Slow storm motion and PWAT values in the mid 20s mm may result in locally large rainfall totals.


... SCOTLAND, IRELAND, NORTHERN IRELAND, N ENGLAND ...

Diurnal heating with cool air aloft will result in scattered showers and a few thunderstorms developing through the day, particularly where upslope flow and/or low-level convergence can force air parcels to rise. Instability is weaker than previous days (eg a few hundred J/kg CAPE), perhaps offset by slightly better DLS, so lightning activity is expected to be less widespread and less intense compared to previous days. Several models simulate convergence zones across the northwest Highlands down towards the Moray Firth, so this area may be one focal point for a few thunderstorms. Severe weather will be limited, although PWAT >20mm coupled with slow moving showers and/or shower training could give some locally high rainfall totals.


... EAST ANGLIA, SE ENGLAND ...

Thunderstorms are expected to develop during Friday night over the Bay of Biscay along and to the east of the surface warm frontal boundary. Given a favourable environment, this may consolidate into an MCS, which ultimately can affect the forecast greatly thereafter. Falling pressure as a wave develops along this frontal boundary is likely to result in a new low pressure centre as the wave moves northwards across northwest France through Saturday morning. With time, it is expected that the western periphery will begin to lose its lightning activity (becoming confined to eastern flank of MCS where better instability exists and proximity is closer to the EML plume), becoming a zone largely dominated by stratiform rain with a few embedded convective elements. This will then extend northwards across southern parts of Britain from mid/late morning onwards (exact track and extent remains uncertain depending on earlier developments over Biscay).

Particular attenton for thunderstorm potential is given to Kent/Sussex from 15z onwards, where destabilisation of the plume occurs within the quasi-warm sector. A mixture of surface-based thunderstorms from France and developing elevated thunderstorms are expected to affect parts of Kent/Sussex later in the afternoon and early evening, migrating northwards across parts of Essex, the southern North Sea and perhaps Suffolk during the evening and first part of the night.

Despite the increasingly elevated nature of such thunderstorms, given MLCAPE locally near 1000 J/kg, hail 1.5-2.0cm in diameter is possible in any stronger cells. Some 40+kts will allow thunderstorms to becoming well-organised and quite long-lived (where they occur), and with PWAT values close to 40mm slow storm-motion is likely to result in very large rainfall totals in a short space of time, significantly heightening the risk of local flash flooding. Considering upgrading some coastal areas in particular to a MDT, but for now remain with SLGT given uncertainties.

Favourable upper level winds will continue to warm advect aloft through the evening across East Anglia, increasing mid-level instability which will be subsequently destabilised, and so it is possible there could be an increase in coverage of scattered elevated thunderstorms over East Anglia through the late evening and early morning hours of Sunday (going beyond this forecast period), and hence a westward extension of the SLGT. Likewise, it is possible that isolated elevated thunderstorms may develop across the Midlands, West Country and east Wales through the evening and early night hours, hence an extension of the ISOL here.

Naturally there is large inter- and intra-model divergence in forecast evolution through the majority of this forecast period, and it is likely updates may be issued as and when necessary to cater for any new developments.

 

http://ukasf.co.uk/storm-forecasts/261

 

[Biggin]

As i am working til 5 tomorrow, anyone got a timetable ie start of rain MCS arrival etc for my area  Its a big ask thanks in advance. surely the models agree on the timing ??

 

Edit just seen above post

Edited July 26, 2013 by Biggin

[kath16]

do you think poor little no major thunderstorms me, will get something in lincolnshire, sick of having to look at lightening in the distance lol

[Convective]

Tomorrow evening into Sunday morning. Yum.

 

[Guest William Grimsley]

do you think Ian's inferring that possible MCS will track further NE into Benelux countries or it's track will be further west than NAE modelling?

 

12z GFS rolling out, shows the higher DLS staying generally across the channel, high PWAT values neat the east coast during the overnight period......some mid level capping in place over the SE quadrant....hmm...some parameters don't look all that favourable for widespread storm activity in CS/SE counties, just lots of rain...however there is decent spread of MLCape over parts of the SE during the night, so who knows at this juncture...

 

here's the 12z GFS precip & MLCape forecasts for tomorrow evening/night

 

1.pbx.png2.pbx.png

 

3.pbx.png4.pbx.png

 

The top-right picture looks very good for Newton Poppleford tomorrow evening now! Will certainly be watching out for some heavy rainfall at a BBQ!

[Paul]

Tornadoes photographed today in both the Isle of Lewis (thanks to Cookie), and also Northern Ireland

https://www.facebook.com/netweather/posts/10151723145279326

[P-M]

Tomorrow evening into Sunday morning. Yum.

 

 

 

It will all be shunted just that little bit further......east 

[Dan the Man]

Just watching Peter Gibbs' forecast - look at those pulses Saturday night!

[VillagePlank]

GooFuS ensemble mean precipitation charts,

 

Overall (Europe),

 

 

Closeup of UK,