Convective / Storm Discussion - 21st April 2014 onwards

[vladthemert]

we just catching the edge of this its raining heavy at moment.  This was not expected but if was not darn mist here I am sure lightening would developed

[Muffelchen]

we just catching the edge of this its raining heavy at moment.  This was not expected but if was not darn mist here I am sure lightening would developed

Yep, the back edge of the precipitation is pepping up as it comes this way. There was a suggestion in comments from the professionals that convection would become elevated during the nighttime hours as it moved north. If this is true then the cold,. murky conditions we are experiencing at ground level may not affect what is going on higher up.

 

Interesting evening I have to say.

[vladthemert]

darn it just starts the thing stops giving false hope

[Vorticity0123]

On the other side of the North Sea, it has been a very exciting day! Unexpectedly, a weak trough has caused a broken line of some very intense convective pulses. Some of the convective cells caused lighting with an intensity of more than 300 strikes per 5 minutes! It has been the most active day of a string of days containing thunderstorms.

 

Synoptic situation

 

A high pressure extending from western Norway all the way toward Ukraine has been located around this area during the past few days. Furthermore, a low pressure area (associated with an upper level trough) is located just to the southwest of Ireland. This low has an extension over the Benelux. The synoptic situation can be seen below:

 

GFS 12Z T+0h. Surface level pressure and 500 hPa heights.

 

The situation resulted in CAPE-values of about 1200 J/kg (at 18Z), sufficiently high for convective development (according to the GFS). Shear values (change of wind speed and -direction with height) were low, though, preventing a high level of organization of the convective cells. {This statement is up for debate, though, as the convective cells were organized in a (curved) line. I don't know whether this was due to the fact that the convergence line (or trough) was stretched northwest-southeast, or due to increased organization of the convective cells}.

 

On the small scale, the trough was only barely visible on the pressure charts. In fact, it could only be noted by a line of convergence of winds. The trough (as of 17 Z) can be seen on the Harmonie (a small-scale, high-res model) below:

 

Harmonie 12Z T+5h. Wind vectors and isobars.

 

The trough is at the time of the image above located at the border between Belgium and the Netherlands, as can be seen by the convergence of the wind vectors near that area.

 

Still, this weak trough was the trigger needed to develop the line of thunderstorms that is currently active over central Holland (as of 22 o'clock local time). It is quite impressive how such a small-scale feature could cause the formation of such an intense line of convection.

 

Unexpectedness of thunderstorms

 

The thunderstorms that developed today were mostly unexpected. Yesterday, the KNMI (the Dutch MetOffice) forecasted that no thunderstorms would develop. This was based on the fact that there would be an inversion present at a height of 1 kilometre which would be strong enough to halt the development of any convection. The forecasted inversion did materialize, and was still present at 12 o'clock local time, as can be seen in the The Bilt sounding below:

 

Sounding of the Bilt (as of 12 UTC).

 

The inversion can be seen by the steep increase in temperature (the righter most fat black line) at around 757 meters. This increase in temperature is visible as the temperature line moves sharply to the right. 

Of note is that also the amount of wind shear can be deduced from these soundings. Just to the right of the sounding, wind vanes per height level are indicated. The difference in wind strength and -direction indicates the amount of wind shear present. In this situation, the wind shear is just about 20 kt.

 

Even though the inversion was present at 12 o'clock local time, the inversion appeared to be too weak to inhibit convection, or in other words, the weak trough appeared to be just enough of a trigger to break down the inversion and cause the very intense convection. This shows how fine the balance is between no showers and a very intense line of thunderstorms.

 

There could be much more said about this storm, but for now, this post will be finished off with a beautiful picture of a developing thunderstorm.

 

Picture of a developing thunderstorm near Tilburg, the Netherlands. Courtesy: Weerwoord.

 

To summarize: a very promising day for the rest of the convective season! That many beautiful storms may follow!

 

BTW: Any remarks or additions are always welcome!

 

Sources:

http://weather.uwyo.edu/upperair/sounding.html

http://www.weerwoord.be/

http://www.weerplaza.nl/weerkaarten/harmonie/?tau=2&element=slp

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

http://www.knmi.nl/

Edited April 25, 2014 by Vorticity0123

[A.J]

The remnants of the Benelux storms are trundling up the east coast of England still spitting out the odd sferic now and again, should be visible off the the Yorkshire coast

[Cakie]

I am sure I can hear rumbling but there is nothing on the charts

[vladthemert]

meteox has us just having 2 strikes lightening with this mist not gonna see them.  Did not hear any thunder.  Its getting lively near norfolk coastline.

[Crepuscular Ray]

I am sure I can hear rumbling but there is nothing on the charts

I find that, too, when I've seen/heard cloud-to-cloud flashes/rumbles. Is there some threshold below which they don't register, like number of strikes within a given timeframe? Or do only CGs register or something?

Edited April 25, 2014 by Crepuscular Ray

[Supacell]

meteox has us just having 2 strikes lightening with this mist not gonna see them.  Did not hear any thunder.  Its getting lively near norfolk coastline.

 

 Am I missing something?

[vladthemert]

 Am I missing something?

 

who knows they have us getting lightening storm too we not getting anything but to be fair thick fog here.  Looking at live feed had few strikes near sherringham not on land mind you supercell. 

[Cakie]

I find that, too, when I've seen/heard cloud-to-cloud flashes/rumbles. Is there some threshold below which they don't register, like number of strikes within a given timeframe? Or do only CGs register or something?

glad it's just not my imagination, I think sometimes it is in cloud which maybe doesn't register as you say

[Sprites]

lol at Vorticity0123, im sure you will have many more storms this summer!!!

[Gorky]

Nice little storm went overhead with a decent amount of lightning and thunder. 

[East_England_Stormchaser91]

At the end of this, the northeast are getting the fun! Well I never... Lol

[Vorticity0123]

lol at Vorticity0123, im sure you will have many more storms this summer!!!

 

The signs are very positive  . We have had a 3-day sequence of storms, which is rather incredible in april! Furthermore, yesterday, hailstones with a radius of about 1 cm were recorded at The Bilt! And finally, the KNMI measured a total of more than 17000 lighting strikes in the Netherlands yesterday!

 

Below is a sequence of radar images of the Nertherlands, at 19 LT as of 23, 24 and 25 April.

 

Radar image of 23 April 19 LT, showing some modest lighting activity.

 

Radar image of 24 April 19 LT, showing disorganized areas of very intense lighting activity.

 

Finally, a radar image of 23 April 19 LT, showing the convective cells being organized in a broken band, also with some very intense lighting activity.

 

Sources:

http://www.buienradar.nl/radararchief?dag=25&maand=04&jaar=2014&uur=19&minuut=00&bliksem=on&soort=0&postcode=

http://www.knmi.nl/cms/content/119218/zomerse_hagel_in_april

Edited April 25, 2014 by Vorticity0123

[Muffelchen]

Strikes have show up near here on NW from those cells we were watching earlier but with the thick fog and the neighbours having a party there was nothing to be seen or heard here. Glad to see that the good folks of Scarborough got to see something though.  :lol:

 

So close but, as I said earlier, an interesting evening and it still has not got above 9°C all day!

[Neilsouth]

So close? It was miles and miles out! Badly wrong, but then estofex did put us in a severe level warning, that always ends up going pete tong

[Sprites]

Vorticity0123.. the Dutch stormchasers must laugh at the U.K.

We are just far enough west to miss out on the thunderstorms, and it is only when the cold fronts leave the U.K that the ingredients phase to give everyone else storms....

Vorticity0123.. the Dutch stormchasers must laugh at the U.K.

We are just far enough west to miss out on the thunderstorms, and it is only when the cold fronts leave the U.K that the ingredients phase to give everyone else storms....

[NL]

At the end of this, the northeast are getting the fun! Well I never... Lol

All we ended up with up here in the north east was heavy rain and squally winds, although the wind did shift the thick fog thankfully..

[Nick F]

Netweather storm forecast for today: http://www.netweather.tv/index.cgi?action=convective;sess=02c98abb31447a4e464615780aceea76

 

 

Synopsis
Upper and collocated surface low will shift ESE across SW Britain later today. An unstable flow will circulate around the low, the risk of thunderstorms predominantly towards the southwest near the low pressure system.

... N SCOTLAND, IRELAND, S WALES and S ENGLAND ...

There is a risk of lightning across the far north of Scotland in the next few hours before morning heavy thundery downpours here clear away north. Otherwise, bands of heavy showers and a few thunderstorms will spiral around the low close to the southwest of the UK today, any thunderstorms that develop will occur mostly in the above areas, though isolated lightning can't be ruled out elsewhere. Winds will generally be unidirectional up through the troposphere, so vertical shear will be weak with no severe weather likely. However, heavy showers/storms will tend to 'train' over some locations, bringing large rainfall totals with a risk of localised flooding. Any showers/storms may produce small hail and gusty winds. Showers and isolated storms continuing across the south and west of England and Wales overnight.
 

Issued by: Nick Finnis

 

[Mokidugway]

Rain cleared strong insolation starting , looks more promising than yesterday's abysmal crud !!!......

[NO LONGER POSTING]

Does look a bit better today than yesterday.. Although I really did get a lot of rain in my location yesterday localised flooding on some roads back from work.. More flash flooding me thinks because it really did come down for a few hours in the afternoon

[Stormyking]

Can we get lucky again today, its been a fantastic start to the year for storms where I am, trying to make the most of it before I move out to Guernsey.

 

Come on Storms!

[Darren Bown]

I think it'll be Wales/SW and Southern England that will get the thundery showers, the rest of us having heavy showers.

[Mokidugway]

Would just like to get first storm of the year !!!.....