Storm & Convective Discussion - 16/07/15 onwards

[BrickFielder]

  Not quite as I envisaged but definitely interesting to watch. The low should I think lift out to the north sea and the delayed movement of the front eastwards will most likely start to happen. Quite a strong jet pushing in across the Bay of Biscay which I think might mess up the modelling a bit for tomorrow.

 

 

Possible storm development towards Bristol and Welsh marches. Not much electrical activity showing up so instability must be limited.

[Spikecollie]

A 15ft wide by 40ft deep hole has appeared in Manchester following heavy rain

 

I hope someone is looking into it...sorry!

[Methuselah]

A 15ft wide by 40ft deep hole has appeared in Manchester following heavy rain

 

A couple of transfer-fees down the drain!

[Condor Vitesse]

A 15ft wide by 40ft deep hole has appeared in Manchester following heavy rain

 

NO That's the start of the Man-Leeds high speed rail link..

[Nick F]

Much of England and Wales is blanketed by cloud cover thanks to the slow-moving fronts, however, we do have some clear skies or breaks in the cloud to allow some warm sunshine across E Sussex, Kent, Essex, Suffolk and Norfolk - with the temp reaching 24C at Norwich and Headcorn in Kent.

 

radar/satellite with rough estimate of fronts circa 1630:

 

Herstmonceux 12z radiosonde ascent adjusted suggests arimass over far SE with enough CAPE (a few 100 j/kg) for thunderstorms with a temp of 22-24C.

 

 

Soundings over Europe where thunderstorms are possible from this site, includes Herstmonceux:

 

http://www.contourmap.ch/hpbo/sounding_europe.aspx

 

 

Clear skies with insolation also over Normandy, a shortwave upper trough visible on WV imagery moving out of France towards SE England and some forcing from an occlusion have triggered some thunderstorms which are pushing out into the Channel recently, these could clip the far SE this evening, given energy available here to keep them going, so one to keep an eye on.

 

WV image:

 

 

Little convective activity along the cold front further west, so really only the far SE in the warm and unstable air likely to see any storms for the rest of the day.

Edited August 14, 2015 by Nick F

[Ellozee]

Hoping I'm far enough SE.. might have to paddle out to sea a bit. Lovely warm and sunny afternoon with a slight cooling breeze.

[Dami]

Off topic -BUT, my eight pennies worth.

 

The problem as I see it in this thread is in the title. It clearly states storm and convective discussion, so people are expecting it just to be that, a discussion, some will agree with what is being said be it forecasts here or else where, some won't, but most have stated that this should be a place for discussing the technical and analytical aspects of storms and cloud formation and therefore should state, for example Storm & Convective TECHNICAL discussion, so people will know their moans to a degree are not in the right place.

 

If I were to be as picky,I would say the moans about the moans has no place on the thread either and is just as annoying.  

 

This thread highlights my personal interest in the weather phenomenon we call storms and i'm slowing coming to grips with what charts mean and don't mean for this.

 

I'm always hosting parties in the NSC, maybe some of you should come visit?

 

Fixed , lol

Edited August 14, 2015 by Dami

[Gael_Force]

Maybe have a banter, moans and ramps thread just like in models section. Keep this discussion thread to forecast charts, storm reports and that will allow the more detailed discussion not to get lost in pages of posts that mean nowt.

[NO LONGER POSTING]

I don't understand sun out here

[Richard Taylor]

Just an observation, as a follower of this thread - I see references to Auntie Beeb, as in: "the BBC had too many lightning symbols" or "Ill never trust the BBC forecasts again" etc.

 

May be just me - and I accept the BBC is many things to many people - but I always thought they were a Public Service Broadcaster, and not weather forecasters. Surely whatever they produce by way of a weather forecast comes courtesy of the Met Office? 

 

By the way, the various airports around the world that do have meteorologists on hand very seldom (indeed if ever) forecast thunderstorms above a 30/40% probability (those interested in aviation will know what I mean when you see PROB30 etc in Terminal Area Forecasts).

 

So if they are cautious, don't take what your App says as gospel!       

[Darandio]

Aren't the forecasters themselves actually from the Met Office?

Edited August 14, 2015 by Darandio

[A.J]

A 15ft wide by 40ft deep hole has appeared in Manchester following heavy rain

 

A 15 mile by 10 mile hole appeared within the M60......It's been named 'Manchester'.......I'll fetch me coat   

[Essan]

Wettest day here since 20th July 2007.

Storm total 39.2mm of which 37.1mm since midnight.  

Has had little effect on river level though!

[Stormyking]

Had some extremely Heavy downpours just over an hour and a half ago, with an almighty crack of thunder rippled through the sky! Was just the one lot though

[Lauren]

Sky very dark and Grey to my south, looks like somethings coming.

[Andy Bown]

Wettest day here since 20th July 2007.

Storm total 39.2mm of which 37.1mm since midnight.  

Has had little effect on river level though!

That might take more effect overnight into tomorrow once water gets into the river system.

[alexisj9]

Sky very dark and Grey to my south, looks like somethings coming.

Can confirm, plus ac cas over head. Fingers crossed the channel does not kill it this time.

[Paul]

Latest Netwx-SR brings some meaty showers/storms through into the southeast/East Anglia this evening..

 

[Mesoscale]

I wonder how many people moaning on here about people moaning get annoyed when their football/sports team doesn't win or their partner getting them the wrong beer or food. Its what the British do best along with queuing. Its not the fact people think they will 100% get a storm, its the fact that they want a storm when most on here hardly get any, if any. Its a big ol' slap in the face when 150 miles to the south in France huge great storms erupt engulfing North France and the Benelux countries, when most of the time we can't even gather up enough energy to muster a fart. 

[Methuselah]

I wonder how many people moaning on here about people moaning get annoyed when their football/sports team doesn't win...

I'm a Spurs fan...Nuff said!

[SnowBear]

Very eerie light in colchester at the moment with light rain, I see the heavy shower which has rolled up off shore along the Essex coast is now over Clacton and has produced a couple of sparks.

Edited August 14, 2015 by SnowBear

[Vorticity0123]

We are at the end of a rather warm, humid, and for some thundery spell of weather. In the Netherlands there were quite some thunderstorms, with more than 20000 lightning strikes recorded.  Ultimately the activity here was much higher than expected previously. On the other hand the UK (reading from the posts) seems to have received much fewer thunderstorms instead. Clearly the situation proved to be a real challenge for forecasters in terms of the pinpointing of thunderstorms.

 

But why was that the case? Was it just the usual uncertainty related to the small scale of thunderstorms which makes it very difficult for models to grasp the exact location? My view is that this was not only the case. Dynamically (or on a larger scale), the situation also proved to be rather complex, perhaps even more than I had foreseen initially. This has also been dealt with in a more concise way by Tamara. In this post I will try to show the complexity of the situation using current model output and a variety of other analysis methods.

 

The large-scale picture

 

Before going into detail immediately, let us first zoom out and look at the current pressure pattern, as shown by the GFS below:

 

GFS 12Z MSLP + 500 hPa heights, Analysis.

 

What we can see is that we are currently experiencing a blocked pattern. As has been the case for much of this summer, a dominant 500 hPa trough (blue circle) is located to the northwest of the UK, with an associated surface low pressure area. This trough has a northwest-southeast orientated extension running through the UK towards the Mediterranean Sea. The low pressure area that has been influencing the UK over the past few days is positioned in the extension of the trough.

 

On the other hand, we can see a rather potent 500 hpa ridge (red line) orientated northwest-southeast from eastern Europe via Scandinavia towards Greenland. This high-over-low pattern is indicative of a blocked pattern.

 

From above

 

If we look into slightly more detail at the 500 hpa heights, we can identify an individual center in the extension of the 500 hPa trough (blue line in GFS image):

 

Visible satellite image as of 12 UTC + 500 hPa heights (green lines).

 

Once again we can discern the deep trough to the south of Iceland, the extension of the trough towards the Mediterranean Sea and the ridge towards Greenland. However, we can also diagnose an individual center over northwestern France and/or southeastern UK.

 

The visible satellite image itself shows a large cloud band beginning  near the Pyrenees which extends northward all the way into the trough to the south of Iceland. There are some irregularities in this cloud band, though, especially over southern France and the Benelux.

 

Frontal analysis

 

Now I will try to do a frontal analysis (only the part that is of importance to the UK) based solely on satellite imagery:

 

Visible satellite image as of 12 UTC + frontal analysis.

 

Blue indicates a cold front, red a warm front and purple is an occluded front . Note that the frontal analysis is purely based on own interpretation and does not (as we will see later) represent reality very well.

 

Here I have connected the cloud band over western France northward as one long front belonging to the low pressure near Iceland. The weak warm front is based on the small extension of clouds just north of the Benelux. For the sharp ones under us, you can already see that the analysis over France is wrong, as cold fronts very rarely have a rightward bend in them.

 

Equivalent potential temperature analysis

 

For our next step, we will go over to the theta-e (equivalent potential temperature) analysis for designating fronts from the WRF-model. If you are unknown with this term, I wrote a brief explanation in a previous post in the Model output discussion thread: https://forum.netweather.tv/topic/83676-model-output-discussion-1st-august-00z/page-17.

 

WRF 06Z Theta-e values at 850 hPa height, T+6h.
 

Once again, this analysis is purely based on own interpretation.

 

Well, honestly, there is very little, if any resemblance of the frontal analysis I made based on satellite imagery, and the one based on equivalent potential temperature.

 

We can still see the cloud band from the low pressure near Iceland towards France is somewhat retained, but here the cloud band exists out of two distinctly different frontal systems. Furthermore, the warm front over Denmark is still somewhat visible, but in the last analysis I have extended it much further.

 

Experts judgement

 

Now that we have seen that my analyses were totally different, let us see how the KNMI (Dutch equivalent of the MetOffice) thinks about the current synoptic pattern.

 

KNMI frontal surface analysis as of 12 UTC

 

Looks rather complicated, doesn’t it? There are a lot of frontal ‘systems’ (or boundaries) stacked very close to each other, that is at least certain. Once again realize that this is just an interpretation, which may be right or wrong. But this time it is from an expert.

 

Let’s now compare the KNMI analysis with mine. First, the double structure of the cloud band from southern France to Iceland was not identifiable on satellite imagery, but theta-e analysis helped a whole lot there. On the other hand, while satellite imagery allowed me to make a curl around the Iceland low, theta-e analysis did not show any clue. For the rest, my theta-e analysis seems to match the KNMI analysis slightly better, but not impressively so.

 

Verdict

 

In the part above I have shown that the frontal analysis was a rather tough one to do – both for me and for experts. But what has this to do with the forecasting of thunderstorms, you may wonder? Well, having the dynamic (synoptic scale) setup right is of great importance for creating a reliable thunderstorm forecast.  If the dynamic situation is just slightly different than expected (imagine an area of very warm/moist air being located just 50 km more towards the south), you can imagine that the risk on thunderstorms also shifts by this distance.

 

How such small distance differences could have major implications on the whole synoptic pattern has been nicely discussed by Tamara a couple of pages back, here a small quote as an illustration:

 

 

Its proved the case that the modelling has very slowly adjusted that stuck frontal boundary from just off the south east coast earlier in the week, some 40 miles, maybe, further northwest. Not much at really, but this has had the effect of skewing the surface pattern enough to considerably change the expected distribution break-out of middle level convection on the northern perimeter of the plume as had been expected mid week.

 

Furthermore, with such complex dynamic situation you can imagine how difficult it is for a forecaster to make a reliable synoptic forecast (let alone a reliable thunderstorm forecast), even with the help of computer models. Even for small-scale models, it is very difficult to capture temperature- and moisture gradients at such short distance correctly. Any mistake there will propagate and be exaggerated further as one moves on with the model run.

 

Concluding, I think that the ‘miss’ in forecasted thunderstorms for some did not only come from the local effect of ‘here I have a thunderstorm but my friend a few miles further does not’, but also from the very complex dynamical situation. It was (and still is) very hard to get your grips around this situation in a logical way, let alone produce a reliable forecast.

 

I hope this post has given some insight in why it was so difficult to predict thunderstorms correctly yesterday and today. One thing remains certain, though: always remain alert, and who knows you can catch some unexpected miracles .

 

Sources:

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

http://eumetrain.org/eport/euro_12.php?width=1366&height=768&date=2015081412&region=euro

http://wolken.buienradar.nl/EU?type=infra

http://www.modellzentrale.de/WRF-medrange/index.php#0

Edited August 14, 2015 by Vorticity0123

[Dean E]

Within the last few minutes, it appears the cold front has passed over here. Humidity now lower and much more comfortable. 

 

And guess what? A great scene to end this humid spell!

 

 

To the next one!

Edited August 14, 2015 by SnowMania

[Mesoscale]

Thanks for the in-depth post Vorticity!  

Storm coming into Hamburg right now, not particularly active but there is intermittent lightning!

http://www.earthcam.com/world/germany/hamburg/?cam=hamburg_hd

 

[Weather-history]

Couple of early morning showers