21st July 2011 - Storm/convective Forecast, Discussion & Reports

[Lauren]

Another storm headache. Why am i getting these if no storm is nearby?

[VillagePlank]

Today looks to turn out to be an interesting weather day. Here's the London Heathrow skew-t for 15z

First thing of note is that the LI is positive. Lifted Index is the difference in temperature between the LCL and the temperature at 500hPa if a parcel is raised adiabatically. It refers specifically to the stability of the atmosphere at that point - in this case 500hPa, or about 5.5km up. Normally one looks to have a negative LI.

Now, around about 550hPa we have a dewpoint depression. So just as we run out of convective steam we get a dry punch aiding convection since the atmosphere beneath that point is bouyant.

Also the wind direction changes with height (particularly between 850hPa and 900hPa) so with a bit of surface heating we might well see some scattered thunderstorms utilising that CAPE - certainly heavy showers - but if they turn into storms, they might well be quite picturesque ...

Edited July 21, 2011 by Sparticle

[Lynxus]

Another storm headache. Why am i getting these if no storm is nearby?

Just a normal headache then

..

Looks like all the bigger showes are going around me again.. Gloucester has an awesome storm shield these last few years.

[VillagePlank]

MetO Invent going for big showers this evening (19z) clearing SE ...

Edited July 21, 2011 by Sparticle

[Coast]

Very humid currently. A colleague at work here said there is a thunderstorm on the way, to which I had to ask why? He says it's an old country feeling! (well probably just as good as models!)

[Thundery Shower]

very dark in near swindon anyone confirm thunder from that area of percipitation?

[Lynxus]

very dark in near swindon anyone confirm thunder from that area of percipitation?

Just rain from what I can tell. Certainly no sferics from what I can see.

[VillagePlank]

Very humid currently. A colleague at work ha said there is a thunderstorm on the way to which I had to ask why? He says it's an old country feeling!

It all feels very still and very quiet, with no birds flying around, the cat came indoors (the cat hates us - we only see her when she's hungry) and is asleep on the sofa. Now, it could be the case that she's eaten all the birds and is trying to sleep off that weighty lunch ...

[tomp456]

It's blobbing with rain here...sky pitch black. Where the thunder?! meh.

[gottolovethisweather]

A quick post from me.

I'm quite positive that I or at least folk in many parts of the south will get a rumble or three today. Why? check out the latest radar grabs and also, just by looking out of the window and from other reports, the skies are truly looking full of it.

Furthermore, currently I'm reading 18.3c with corresponding dewpoint of 14.8c (earlier reached 15c) so a fair few factors are coming together.

Note the wind vectors on the second radar grab which indicate the direction the showers/storms are moving.

Thundery Regards

gottolovethisweather

[VillagePlank]

It's blobbing with rain here...sky pitch black. Where the thunder?! meh.

Much more likely, in my view, between 18z and 20z.

Note the wind vectors on the second radar grab which indicate the direction the showers/storms are moving.

I'd go for the direction of showers to rotate to head SE as we move on into evening ,..

[Lauren]

Just a normal headache then

..

Looks like all the bigger showes are going around me again.. Gloucester has an awesome storm shield these last few years.

No, it's very different headache to a normal headache. It's sort of buzzing.

[Coast]

Cant find any current soundings for Herstmonceux, even the NW extra one is well out of date and Weather Online is a few days old. Must be a problem with the radiosonde.

[gottolovethisweather]

Much more likely, in my view, between 18z and 20z.

I'd go for the direction of showers to rotate to head SE as we move on into evening ,..

Interesting, do you think will that increase our changes, well my chances in Newbury, Berkshire?

Also, do you happen to know what sort of cape reading/lifted index reading is favourable for storms, currently showing 200 cape and +3 li ?

Cheers

gottolovethisweather

[Lynxus]

No, it's very different headache to a normal headache. It's sort of buzzing.

Ahhh

That will be a Bee.

See I could be a doctor!

..

Some fairly good looking convection going on around here.

Id personally be shocked if anything other than a heavy shower hits here ( or anywhere ) today.

[Coast]

Also, do you happen to know what sort of cape reading/lifted index reading is favourable for storms, currently showing 200 cape and +3 li ?

[VillagePlank]

lso, do you happen to know what sort of cape reading/lifted index reading is favourable for storms, currently showing 200 cape and +3 li ?

As a general rule, the higher the CAPE, the better: also, generally, for t/storm formation LI should be negative. We have a small amount of CAPE around Heathrow this evening c.400j/kg, and positive LI - so on the face of it, it doesn't look promising. However, these are not the only formative factors indicating t/storm development. For instance, if the wind converges on itself then that will force air up - if air goes up the temperature cools and the water in that air condenses out to form clouds - the bigger the clouds the more chance of a t/storm.

Today, some of our lift will come from surface heating - it looks like no problem to get cloud tops to 15,000ft today, but also, today, we are expect an occluding front (a front that is weakening because the air mass in front of it, and behind it are mixing) to travel SE across the country:

.. and because the air is colder aloft than below, that generates bouyancy. There's also the opportunity for a dewpoint depression - an area where the air is dry - to kick the air beyond the 15,000ft layer - but the physics of why that is the case is beyond a simple post like this one.

Certainly some very heavy showers today - as NF said, the amount of precipitable moisture is high, today - and, if lucky, we could get a light show.

Edited July 21, 2011 by Sparticle

[gottolovethisweather]

Thank Coast once again.

So maybe not so favourable today then? However, I'm sticking with gut feeling and observations, things can change for the better and they're are plenty of other factors to consider so alls well.

Hope you get something too.

Stormy Cheers

gottolovethisweather

[Harry]

Very humid currently. A colleague at work here said there is a thunderstorm on the way, to which I had to ask why? He says it's an old country feeling! (well probably just as good as models!)

Glad it wasn't me! Humidity feels to have leapt up some what...windows open now in office, rather stuffy!

Wall to wall light grey skies though...if it thunders/pours down, it's going to be one of those days where you don't see it coming

[gottolovethisweather]

As a general rule, the higher the CAPE, the better: also, generally, for t/storm formation LI should be negative. We have a small amount of CAPE around Heathrow this evening c.400j/kg, and positive LI - so on the face of it, it doesn't look promising. However, these are not the only formative factors indicating t/storm development. For instance, if the wind converges on itself then that will force air up - if air goes up the temperature cools and the water in that air condenses out to form clouds - the bigger the clouds the more chance of a t/storm.

Today, some of our lift will come from surface heating - it looks like no problem to get cloud tops to 15,000ft today, but also, today, we are expect an occluding front (a front that is weakening because the air mass in front of it, and behind it are mixing) to travel SE across the country:

.. and because the air is colder aloft than below, that generates bouyancy. There's also the opportunity for a dewpoint depression - an area where the air is dry - to kick the air beyond the 15,000ft layer - but the physics of why that is the case is beyond a simple post like this one.

Certainly some very heavy showers today - as NF said, the amount of precipitable moisture is high, today - and, if lucky, we could get a light show.

What a great explanation, cheers Sparticle.

gottolovethisweather

PS! now big spots of rain here in RG14 but I await more.

[VillagePlank]

Perhaps, more than a marginal chance of seeing a funnel cloud today?

Look at how all those wind arrows are going in different directions! (of course, the wind isn't at all strong so tornadoes seems unlikely)

Eyes up

Edited July 21, 2011 by Sparticle

[Flash Elvis]

Got no sunshine but things warming up now...somehow?

Will be watching the Weather at Lords as 99% of the time what weather they get there, we get in Rayleigh.

Plenty of action over Belgium & Holland as usual !!!!

Edited July 21, 2011 by Flash Elvis

[Lynxus]

hahaa, all the bigger showers have been going around the valley that glos and chelt is in.

Storm Shield at max powah!

[Andy Bown]

Very interesting to watch how the energy in the showers is transferring.

At 13.30 the showers to my NE were most powerful in there SE/E section but as they've edged SSW over the last 90 minutes the

energy has transferred to the W/NW section.

If you want to see what I mean type in BA12 in the NW radar postcode zoomer & follow the showers from 13.30 to the latest time.

[SteveB]

All those showers seem to be heading my way, hopefully something will come of it.