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AWD

Stormy Wednesday 15th August 2012

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To save cluttering up the main thread with Wednesday's potential and observations of todays activity, I thought it best to have a seperate thread to discuss in more detail the threat that Wednesday may bring. ( if not warranted, please delete ).

I am particularly interested in the potential, probably because it is the next opportunity for action in my area, but also because some of our more knowledgable members are talking of a possible severe weather event.

As i understand it so far, there are two fronts forecast to pass over the UK on Wednesday. The first one is forecast to be frontal rain only. Inbetween the first front and the second front is the warm sector where temps are forecast to get up to the mid twenties along with high humidity. It is in this area, along with the second front, a cold front, that thudnerstorms could break out, these containing large hail, frequent lightning and tornadic activity.

post-12721-0-48248100-1344852727_thumb.p

However, a look through the convective charts don't through anything "bullish" to me at all, except the tornadic activity, which does look promising.

This is how the HirLam model as the system at noon Wednesday.

post-12721-0-72560000-1344852940_thumb.p

Notice the second batch of PPN in the Atlantic, south of Ireland. Is that the cold front that is expected to bring the thundery conditions?

The first front on that chart doesn't have much in the way of Lapse/Sheer/Cape/Convergence associated with it, so this must be the first frontal rainband expected.

On the below chart, we can see the humid air coming up over the UK.

post-12721-0-56740300-1344853117_thumb.p

The Beeb/Meto do not mention nothing in the way of thundery activity on Wednesday however!

Perhaps the more knowledgable members would be kind enough to put their thoughts and forecasts in here when they are ready too. That way people like me, who find this type of scenario totally new, will be able to understand and look forward to any potential coming our way.

Thanks!

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clapping.gif I like it because it suggests this:

54_48.gif

54_20.gif

60_20.gif

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To be honest, I was rather hoping for a few more "Reds" in there, a bit more widespread. Anywho, this is why I'm a little confused on this one, different charts show different things and little talk of it from the Meto.

Would have thought a yellow advisory would suffice by now if they were expecting something to materialise.

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It doesn't seem to be that widespread until it exits into the North Sea. I'm liking my local SkewT for first thing in the afternoon:

sounding3.curr.1400lst.d2.png

cape.curr.1400lst.d2.body.png

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The MO have put yellow warnings out for rain on Wednesday, just covering parts of the west, and Ireland.

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GFS has a lot going on Wednesday afternoon from around 12z to 15z:

post-6667-0-86450300-1344856742_thumb.pn

post-6667-0-52439900-1344856748_thumb.pn

A lot of it is rain!!!

post-6667-0-07292900-1344856753_thumb.pn

post-6667-0-52555500-1344856758_thumb.pn

post-6667-0-34476500-1344856764_thumb.pn

Look at the helicity going on:

post-6667-0-63583400-1344856768_thumb.pn

and that Theta E that is a feature of today's potential:

post-6667-0-94698900-1344856774_thumb.pn

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Models are firming up on a stormy wednesday with Gales possible in exposed areas and heavy rain the met office have weather warnings out

Issued at - 13 Aug 2012, 11:51

Valid from - 15 Aug 2012, 06:00

Valid to - 15 Aug 2012, 23:59

Heavy rain, accompanied by strong winds, is expected to spread north during Wednesday morning and afternoon, to affect parts of western England, much of Wales and Northern Ireland. The heaviest rain is likely to clear from the south by evening, but the strong winds may peak a little later. The public should be aware of the possibility of surface water flooding and the likelihood of difficult conditions for travel and some summer holiday pursuits.

http://www.metoffice...ather/warnings/

ukprec.png

ukprec.png

ukprec.png

Wind Gust's will be upto 50mph

ukwind.png

ukwind.png

ukwind.png

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Hmmm, looks good/interesting in the north west. Think I might refasten the tarp that's keeping the rain out of my garage!

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GFS has a lot going on Wednesday afternoon from around 12z to 15z:

post-6667-0-86450300-1344856742_thumb.pn

post-6667-0-52439900-1344856748_thumb.pn

A lot of it is rain!!!

post-6667-0-07292900-1344856753_thumb.pn

post-6667-0-52555500-1344856758_thumb.pn

post-6667-0-34476500-1344856764_thumb.pn

Look at the helicity going on:

post-6667-0-63583400-1344856768_thumb.pn

and that Theta E that is a feature of today's potential:

post-6667-0-94698900-1344856774_thumb.pn

Some good charts there for the Eastern side of the country into the Midlands for sure.

ML Cape could do with being improved however.

Perhaps a gathering around Coasts' house is required on Wednesday then?

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thanks COAST for all that info ,lets all now enjoy the upcoming weather and i look foreward to the posts , tonights met office fax will be interesting as the charts are or will be firming up .cheers help.gifdrinks.gif

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Not able to quote for some reason!

anyway, in relation to part of AWD's opening post about the BBC/Met not mentioning much about Wednesday ...

...

Neither did they in the build up to Saturday night/yesterday morning yet look what happened in many parts of the West Country!

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Think it's a good idea for a seperate area for discussion of Wednesday's severe convective potential. The sad thing is, though, is that many are oblivious to the potential. Obviously my thoughts yesterday weren't enough to stir up interest for many on the forum, so think further input from me is pointless.

I'll leave it to others to discuss.

Nooooooo. Tell me your thoughts mate, your one of the members i take the most interest in on this thread. That's why I made a separate thread, basically because of what you and Nick F think.

Haven't had a chance to look through the 12z output yet, but the earlier high res charts showed some good sypnotics.

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Lets see what I can make of the 12z output so far then, GFS inparticular.

We have Cape over the Midlands, both SB & ML.

post-12721-0-01563300-1344882412_thumb.ppost-12721-0-59602700-1344882426_thumb.p

post-12721-0-01646300-1344882440_thumb.ppost-12721-0-58084200-1344883079_thumb.g

With a high humidity plume coming up from the continent over South East, Central Southern England & the Midlands

post-12721-0-00467500-1344882502_thumb.ppost-12721-0-39729200-1344882518_thumb.ppost-12721-0-83178600-1344882529_thumb.g

After the passage of a "normal" frontal band of rain, this plume will create a warm sector, destabilising the following cold front and could cause thunderstorms, perhaps severe, to form over the mentioned areas. With high humidity values too, intense rainfall is likely, leading to some flooding.

post-12721-0-81888700-1344882807_thumb.ppost-12721-0-39693200-1344882817_thumb.g

Definetly going to be very wet & humid to say the least.

Will there be thunderstorm/thundery activity though.

post-12721-0-35236700-1344882864_thumb.ppost-12721-0-95119500-1344882876_thumb.ppost-12721-0-87604500-1344882887_thumb.p

post-12721-0-19414300-1344882904_thumb.ppost-12721-0-40923400-1344882925_thumb.ppost-12721-0-59994000-1344882942_thumb.p

From what I can see, the ingredients are definetly there for thunderstorms to develop over Southern, Eastern England and the Midlands.

Tornadic activity also looking decent across most of England and Wales. Strong signals from the chart below.

post-12721-0-93903200-1344883045_thumb.p

This, IMO, is a very unusual set up for the UK. Media forecasts & the Met Office might not pick up on the potential for this event until much nearer the time, if indeed they do at all.

Just look at the Jet Stream, how often do you see such a strong jet arch across the UK, "reversing back" travelling east to west.

post-12721-0-09439000-1344883191_thumb.p

And finally the PPN. It is going to be heavy. The Meto do have a warning out for Western parts of England, Wales and parts of Ireland already, expecting heavy rain, strong winds and localised flooding. I expect this warning to expand nearer to the event, including the Midlands and Southern England where I think, due to the humidity, the rain will be much heavier than what is currently progged.

At 12z Wednesday, the PPN is forecast to be over South West England , South West Wales and Southern Ireland.

post-12721-0-91547200-1344883331_thumb.ppost-12721-0-75177400-1344883389_thumb.g

post-12721-0-04154600-1344883531_thumb.gpost-12721-0-12834700-1344883540_thumb.g

Widely 25mm, locally 50mm towards the west and north.

Going to be windy too, with gales or even severe gales down towards the South West.

post-12721-0-97746000-1344883689_thumb.ppost-12721-0-87292200-1344883699_thumb.j

One thing I have noticed though, and I'm not sure it is such good news for thunderstorm development is a difference between last nights FAX and tonight FAX

post-12721-0-55197500-1344883764_thumb.ppost-12721-0-11782400-1344883772_thumb.g

The latest Meto Fax now suggests an attached arm to the cold front, which may mean the "humid air" is prevented from getting across the country. Perhaps a more knowledgable member could elaborate on this?

Anyway, to summarise, a very wet and windy day for sure on Wednesday. Flooding is likely, especially across western areas. The Midlands and parts of Southern & Eastern England are at risk of thundery developments as warm, humid air gets avected across the country frok the continent, although this will be affected by the speed of the cold front.

Potential is still there for a severe weather event though guys! Wouldn't want to be on holiday in Cornwall that day, for sure!

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Lets see what I can make of the 12z output so far then, GFS inparticular.

We have Cape over the Midlands, both SB & ML.

post-12721-0-01563300-1344882412_thumb.ppost-12721-0-59602700-1344882426_thumb.p

post-12721-0-01646300-1344882440_thumb.ppost-12721-0-58084200-1344883079_thumb.g

With a high humidity plume coming up from the continent over South East, Central Southern England & the Midlands

post-12721-0-00467500-1344882502_thumb.ppost-12721-0-39729200-1344882518_thumb.ppost-12721-0-83178600-1344882529_thumb.g

After the passage of a "normal" frontal band of rain, this plume will create a warm sector, destabilising the following cold front and could cause thunderstorms, perhaps severe, to form over the mentioned areas. With high humidity values too, intense rainfall is likely, leading to some flooding.

post-12721-0-81888700-1344882807_thumb.ppost-12721-0-39693200-1344882817_thumb.g

Definetly going to be very wet & humid to say the least.

Will there be thunderstorm/thundery activity though.

post-12721-0-35236700-1344882864_thumb.ppost-12721-0-95119500-1344882876_thumb.ppost-12721-0-87604500-1344882887_thumb.p

post-12721-0-19414300-1344882904_thumb.ppost-12721-0-40923400-1344882925_thumb.ppost-12721-0-59994000-1344882942_thumb.p

From what I can see, the ingredients are definetly there for thunderstorms to develop over Southern, Eastern England and the Midlands.

Tornadic activity also looking decent across most of England and Wales. Strong signals from the chart below.

post-12721-0-93903200-1344883045_thumb.p

This, IMO, is a very unusual set up for the UK. Media forecasts & the Met Office might not pick up on the potential for this event until much nearer the time, if indeed they do at all.

Just look at the Jet Stream, how often do you see such a strong jet arch across the UK, "reversing back" travelling east to west.

post-12721-0-09439000-1344883191_thumb.p

And finally the PPN. It is going to be heavy. The Meto do have a warning out for Western parts of England, Wales and parts of Ireland already, expecting heavy rain, strong winds and localised flooding. I expect this warning to expand nearer to the event, including the Midlands and Southern England where I think, due to the humidity, the rain will be much heavier than what is currently progged.

At 12z Wednesday, the PPN is forecast to be over South West England , South West Wales and Southern Ireland.

post-12721-0-91547200-1344883331_thumb.ppost-12721-0-75177400-1344883389_thumb.g

post-12721-0-04154600-1344883531_thumb.gpost-12721-0-12834700-1344883540_thumb.g

Widely 25mm, locally 50mm towards the west and north.

Going to be windy too, with gales or even severe gales down towards the South West.

post-12721-0-97746000-1344883689_thumb.ppost-12721-0-87292200-1344883699_thumb.j

One thing I have noticed though, and I'm not sure it is such good news for thunderstorm development is a difference between last nights FAX and tonight FAX

post-12721-0-55197500-1344883764_thumb.ppost-12721-0-11782400-1344883772_thumb.g

The latest Meto Fax now suggests an attached arm to the cold front, which may mean the "humid air" is prevented from getting across the country. Perhaps a more knowledgable member could elaborate on this?

That may well be the problem regarding the development of storms. Comments are being made in various threads about the potential for such an event on Wednesday. Yes its a potential and has to be watched but the Fax change suggests that Met O fine mesh data is leading them to feel that the threat is less than it was say 24 hours ago.

As with every case of precipitation, unstable air or not, the issue is unlikely to be resolved until 12 hours before the event, even then do not be surprised by surprises!

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Think it's a good idea for a seperate area for discussion of Wednesday's severe convective potential. The sad thing is, though, is that many are oblivious to the potential. Obviously my thoughts yesterday weren't enough to stir up interest for many on the forum, so think further input from me is pointless.

I'll leave it to others to discuss.

fool.gif .....Give me strength!!....What a daft thing to post mate....There is plenty of interest, due in part to your 'heads up'...This specialist thread is proof of that!.... so with that in mind, get that bee out of your bonnet and start posting!! biggrin.png

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Some impressive Velocity being shown by the GFS

post-12721-0-88457200-1344891189_thumb.g

Soaring Index

post-12721-0-95014800-1344891207_thumb.g

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the 12z fax for Wednesday issued at 1740 something today has the warm sector (back again?) and a trough in it?

http://www.weatherch...kmomslp.htm#t60

post-12721-0-58825600-1344892991_thumb.g

Are you referring to this FAX John?

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I think so, although there is no time issue showing; it looks the same with the trough in the warm sector?

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post-12721-0-29787400-1344893281_thumb.g

It's the same 12z FAX as I posted earlier. The above one shows the first front now "attached" to the following cold front. Comparing it too yesterdays FAX;

post-12721-0-66308400-1344893356_thumb.p

Which has two seperate fronts, allowing a warm sector to establish inbetween the two fronts. On the updated FAX, with the warm front being "attached" to the cold front, I'm not so sure how much of an influence the warm, humid airmass forecast to advect into the UK from the continent, will have on destabilising the cold front.

But to be honest, I'm not clued up on this type of scenario. I just feel yesterday's FAX was more proimising for thunderstorm development than todays FAX is, but I maybe totally wrong there!

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post-12721-0-29787400-1344893281_thumb.g

It's the same 12z FAX as I posted earlier. The above one shows the first front now "attached" to the following cold front. Comparing it too yesterdays FAX;

post-12721-0-66308400-1344893356_thumb.p

Which has two seperate fronts, allowing a warm sector to establish inbetween the two fronts. On the updated FAX, with the warm front being "attached" to the cold front, I'm not so sure how much of an influence the warm, humid airmass forecast to advect into the UK from the continent, will have on destabilising the cold front.

But to be honest, I'm not clued up on this type of scenario. I just feel yesterday's FAX was more proimising for thunderstorm development than todays FAX is, but I maybe totally wrong there!

The introduction of warm moist air connected to a trough in a warm sector can, hard to say how many times out of 10 instances this might occur, but is a forecasters short hand for highlighting the possibility of convection in the warm sector. Convection is not normally a feature in warm sectors unless this feature occurs. Difficult to say whether that will mix with the immediate air ahead of the cold front causing deeper than expected instability on the front.Met must be having some difficulty assessing the actual risk as their own NAE model is showing the centre much deeper than their own global model or either GFS or ECMWF. Again their NAE model is showing falls of 20+mm on the south coast in a 6 hour period, considerably more and earlier than the GFS output, both are 12z issue.

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Oww this is panning out to be interesting, but let's hope not destructive. I'll start with a repost of the SkyWarn watch for the period:

SKYWARN UK SEVERE WEATHER WATCH #048

ISSUED: 1500UTC MONDAY 13TH AUGUST 2012

SKYWARN UK HAS ISSUED A SEVERE WEATHER WATCH FOR THE FOLLOWING REGIONS:

ALL AREAS UK

IN EFFECT FROM 0000UTC WEDNESDAY 15TH UNTIL 1500UTC THURSDAY 16TH AUGUST 2012

BISCAY LOW DEEPENS TO ~980MB INTO THE SOUTHWEST, DRIVING STRONG INSTABILITY AHEAD OF AN ACTIVE COLD FRONT WITH GALES FOLOWING

THERE IS A POSSIBILITY OF SEVERE WEATHER AFFECTING THE INDICATED REGIONS IN THE TIME PERIOD SPECIFIED. THREATS WITHIN THIS WATCH INCLUDE, BUT ARE NOT LIMITED TO: HEAVY RAIN...FLOODING...GALES...STRONGER GUSTS...FUNNELS/TORNADOES

DISCUSSION:

THERE IS ADEQUATE MODEL AND AGENCY CONFIDENCE IN A SEVERE WEATHER RISK THROUGH WEDNESDAY INTO THURSDAY TO WARRANT EARLY ISSUANCE OF A WATCH. A LOW DEVELOPS UNDER A STRONG JET CORE IN THE BISCAY AREA AND SOUTHWEST APPROACHES, DEEPENING TO PERHAPS BELOW 980MB WHICH IS UNUSUAL FOR SUMMER. A VERY WARM AND MOIST AIRMASS WILL BE ENCOURAGED NORTH FROM FRANCE AHEAD OF THIS, PROVIDING POTENTIAL FOR EXTREMELY HEAVY RAIN IN RELATIVELY SHORT PERIODS AS THE FRONT PUSHES ACROSS THE UK. ACCUMULATIONS OF UPTO 40MM LOOK LIKELY IN MOST AREAS, WITH SOUTH AND SOUTHEAST FACING SLOPES POSSIBLY HIGHER GIVEN STRONG WINDS ALONG THE FRONT. SOME CONVECTIVE INITIATION IS POSSIBLE AHEAD OF AND WITHIN THE FRONTAL ZONE, PROVIDING FOR POSSIBLE PRECIPITATION AND WIND ENHANCEMENT AS DIRECTIONAL SHEAR IS FAVOURABLE FOR ORGANISATION AND POSSIBLY FOR FUNNELS OR TORNADOES. STRONG THUNDERSTORMS IN FRANCE MAY ALSO CROSS THE CHANNEL IN THE EARLY HOURS OF WEDNESDAY AFFECTING MOST AREAS OF THE SOUTH COAST. BEHIND THE FRONT CLOSER TO THE LOW CENTRE, GALES ARE LIKELY WITH GUSTS PERHAPS EXCEEDING 60MPH, MAINLY AROUND AREAS BORDERING THE CELTIC AND IRISH SEAS BUT ALSO HIGH GROUND OF WESTERN MAINLAND UK AND EXPOSED AREAS OF NORTHERN IRELAND. THIS WATCH WILL BE UPDATED AND POSSIBLY UPGRADED.

It looks like it could cover a huge swathe of the UK:

050328Z_21OWS_ATLANTIC-EUROPE_FITL_THUNDERSTORM-STANDARD_12081506.GIF

045950Z_21OWS_ATLANTIC-EUROPE_FITL_UL-TURBULENCE-STANDARD_12081506.GIF

Quite significant rainfall?

004934Z_21OWS_AFWA-GEPS-PRODUCTS_MODEL-DATA_ENSEMBLE_PROB-OF-2-IN-12-RAIN_ENSEMBLE_54_12Z.png

gfs_prec_eur36.png

and of course, as you would expect there is some extreme shear and helicity up there:

gfs_stp_eur36.png

gfs_srh_eur36.png

Convective gusts midday:

gfs_gusts_eur36.png

10M winds start building from midday in the Channel approaches and on the West Scottish coast:

36_21.gif

42_21.gif

Beaufort wind-scale:

36_45.gif

42_45.gif

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Looking a bit later on, that heavy rain is around for a while:

gfs_prec_eur39.png

gfs_prec_eur42.png

and jeez is that messy for shear - tornadoes, spouts, funnels?

gfs_stp_eur39.png

gfs_stp_eur42.png

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Further to Weather09's post earlier, I think there's little in the way of a frenzy because it's not yet clear whether there is anything worth ramping (from a thunderstorm point of view)

Certainly we have some superb ingredients for some pretty violent weather - torrential, long lived rainfall events are possible in many areas, v strong to gale force winds near the depression, v high levels of moisture, great shear, a very strong jet, surface and mid level instability....the question mark remains over the nature of any thunderstorms which may occur and also, where they might occur.

Should be a heck of squall going through as the CF clears though I imagine and if discreet cells are unlikely, a strong and potentially tornadic squall could indeed be possible.

Interestingly, the MetO's very for my part of the world is for "occasionally heavy rain".....everything I've seen points to something a bit more lively than that, even if not thundery!

Slightly further afield, Sunday evening/nights chart is looking much more interesting for the SE quadrant of the UK, in particular (as always these days) the Midlands, EA and NE England...whilst GFS was sceptical this time yesterday of any precip this weekend, it now thinks there could well be some very intense precip in the aforementioned areas.

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There looks like there could be a chance of thunderstorms wrapped up with everything else nature is likely to throw at us tomorrow!

004905Z_21OWS_AFWA-GEPS-PRODUCTS_MODEL-DATA_ENSEMBLE_PROB-OF-LTG-STRIKE_ENSEMBLE_54_12Z.png

36_20.gif

36_24.gif

and that rain!!!

42_20.gif

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