Storm and convective discussion 7th July Onwards

[Chris101]

My partner works for UK power which covers East of a line from roughly Bognor to The Wash, they have just been given a warning of Heavy Thunderstorms with frequent lightning from 00.01 Saturday to 12.00 Sunday, preparations for staff coverage are well underway.

[Hellboy]

Warming up really quickly here. Seems like the weather is making everything crazy as my forecast for Friday (based on GFS 00Z) shows lightning with 0% cloud cover. :rofl:It's ok though, on Saturday I'll be having storms with nearly 100% cover. 

[vladthemert]

just found this apparently small tornado 1st july did some damage to cars property in hampshire.  

 

http://www.itv.com/news/meridian/update/2014-07-01/eyewitnesses-describe-tornado-like-an-explosion/

[NorthNorfolkWeather]

Then again GFS 6z for Saturday looks even more widespread further westwards too?!

 

Saturday looks incredible for ALL of England!

As TEITS said in his post, there will undoubtedly be winners and losers, but we're nearing a reliable time and, if anything, the charts are upgrading.

 

The graphic on BBC breakfast at 08:45 showed pulses of weather mainly towards the Midlands and East, but we're still too early to put an accurate track these  --  it's still all potential.

 

Will come down to streetlight watching (whoops, wrong time of year) nowcasting and Radar watching

Warming up really quickly here. Seems like the weather is making everything crazy as my forecast for Friday (based on GFS 00Z) shows lightning with 0% cloud cover.

It's ok though, on Saturday I'll be having storms with nearly 100% cover.

 

Would that mean you get a proverbial "Bolt from the Blue"?

[NorthNorfolkWeather]

My partner works for UK power which covers East of a line from roughly Bognor to The Wash, they have just been given a warning of Heavy Thunderstorms with frequent lightning from 00.01 Saturday to 12.00 Sunday, preparations for staff coverage are well underway.

 

Hellfire, that's a bit precise. 

 

I'll have to go to bed early to get up for the spectacle

[Chris101]

Thoughts of PJB on UKww, GFS has moved towards the ECM today, first trough Thursday night see's storms firing from Lyme bay Westwards. NOTE- Storms will NOT be routed aloft but will initialize from destabilisation of the 850 level.

 

Friday night, strong destabilisation occurs and a greater than 50% chance of an MCS forming over N France and the Channel moving into CS England and parts of the SE, UKMO is slightly further East with this. Storms will initially be routed aloft but will merge with surface based convection on Saturday with further heavy thunderstorms breaking out.

 

http://www.ukweatherworld.co.uk/forum/index.php?/topic/104182-spanish-plume-for-18th19th/page__pid__906717__st__40#entry906717

[alr1970]

A question, when we, or mainly you all talk about "CAPE" and the lifting of air, is all air equall when it comes to weight? I just imagine a parcel of "DRY" air, would weigh considerably less than a parcel of "MOISTURE RICH" air, which in normal terms and everyday physics would therefore need less energy to lift it? Also, lifting "DRY" air, wouldn't result in convectiveness, because their would be nothing to condense out of the dry air?

 

Am I making any sense?

You're making sense, yes, but moist air is actually less dense than dry air.

 

Did you do physics at school? Do you remember the Ideal Gas Law?

 

It states that PV=nRT, where P is pressure, V is volume, n is the nuber of molecules, R is a constant and T is the temperature, Kelvin. Amonst other things, it explains why the temperature of a gas increases when you compress it.

 

In the case of dry/moist air, it means that at the same pressure and temperature, you get the same number of molecules in a fixed volume, regardless of what exact molecule they are. So an oxygen molecule takes the same amount of space as a nitrogen molecule, or a water molecule. The relative weights of molecules can be calculated from the sum of atomic weights of their constituent atoms:

Oxygen, O2, is 2x16=32

Nitrogen, N2, is 2x14=28 (no significant difference so they mix freely in the atmosphere)

Carbon dioxide, CO2, is 6+2x8=38 (significantly heavier so it can accululate in low places if emitted in sufficient quantities, such as from a volcano)

Hydrogen, H2, is just 1x2=2

Helium, He, is just 4, which explains why you can float things with them

And finally, water H2O, is 1x2+8=10

 

So if you can replace some of the oxygen and nitrogen with water, the density drops and it will bob up. I can't find exact numbers, but I think 1m3 of 100% huimid air contains about 30g of water at 30C, about 2.5% of the total mass.

 

http://en.wikipedia.org/wiki/Density_of_air#Humidity_.28water_vapor.29 might help explain some of this.

[Chris101]

Hellfire, that's a bit precise. 

 

I'll have to go to bed early to get up for the spectacle

You don't want to be oversleeping, go to bed at 12.01 Sunday

[Lauren]

Haven't seen one of these issued for a long time.

 

http://www.metoffice.gov.uk/public/weather/heat-health/#?tab=heatHealth

[lassie23]

The last time there was a health warning was last July!

[Mapantz]

It's also a bit precise to say storms will fire from Lyme Bay and west..

[Nick L]

A question, when we, or mainly you all talk about "CAPE" and the lifting of air, is all air equall when it comes to weight? I just imagine a parcel of "DRY" air, would weigh considerably less than a parcel of "MOISTURE RICH" air, which in normal terms and everyday physics would therefore need less energy to lift it? Also, lifting "DRY" air, wouldn't result in convectiveness, because their would be nothing to condense out of the dry air?

 

Am I making any sense?

 

Dry air is actually MORE dense than moist air. I'm working at the moment but hopefully I'll get back to this later.

[NorthNorfolkWeather]

Words of caution (before we get too excited) from the MO chief forecaster

 

From the MO Weather Warnings page

In this situation many elements need to come together at the same time to form these thunderstorms and so there remains large uncertainty in their development. This alert is therefore likely to be updated in the coming days.

Edited July 16, 2014 by NorthNorfolkWeather

[William Grimsley]

 

Words of caution (before we get too excited) from the MO chief forecaster

 

From the MO Weather Warnings page

In this situation many elements need to come together at the same time to form these thunderstorms and so there remains large uncertainty in their development. This alert is therefore likely to be updated in the coming days.

This is for Saturday not for Thursday Night's possibility.

[saint]

This is for Saturday not for Thursday Night's possibility.

I think that was the point

[Bobby]

ECM precip chart for Thursday night, the storms part like the Red Sea as soon as they near here. It's so going to happen like that

 

 

Crazy amounts of CAPE on Friday night in the SE, looks like big MCS imports and homegrown storms, could be severe

 

Edited July 16, 2014 by Bobby

[Speedway Slider]

What about this afternoons Chances ? It was included in todays forecast, well the ones in the witching hours........!!!

[Speedway Slider]

Just looking at the rain radar, the showery, raggety stuff moving east has now developed a really sharp and defined line at its front (leading edge) Is this a sign of it bashing into the high pressure? (See attached) NOW!! 

Edited July 16, 2014 by Speedway Slider

[Chris101]

It's also a bit precise to say storms will fire from Lyme Bay and west..

Thats what the latest ECM is saying, so i don't think hes being precise, he's saying it how the models are seeing it and GFS has swung towards the ECM now aswell, which is no surprise to me, it was pushing things through way too fast.

 

IMO PJB is one of the best convective forecasters on any of the forums (not saying that NW doesn't have a few very good ones too) but i certainly wouldn't ever ignore his thoughts, with just over 24 hours till the first shortwave makes its move i would certainly be expecting things to be firming up now with regards to where and when.

[Summer Sun]

Latest text update from the met

 

Outlook for Friday to Sunday:

 

An increasing chance of very heavy, thundery downpours moving northwards Friday and Saturday. Further showers on Sunday, less widespread than Saturday. Hot in the south and feeling humid for many.

[TheToastPeople]

Ahh i see the ramp is in full progress, Not going to bother looking at the charts it always leads to major disappointment on the day. Although I will charge the camera and keep an eye on the radar just in case!

[A.J]

Getting excited at the potential of seeing severe storms. The use of the word "Severe" is often over used on this thread but with the current set up for later this week/weekend, we could genuinely see severe storms.

 

Im not focussing too much yet on the models or the BBC/Met O forecasts because past experience tells me its pointless. I have no doubts there will be winners & losers and sometimes it simply boils down to luck and timing. For example a severe storm could move up from the channel overnight and weaken to leave a band of cloud and rain during the day preventing convection from kicking off.

 

For guidance I shall be following Nick F forecasts. I find these the most accurate and are even better than the Met O. What I like about Nick F isn't just his knowledge but he isn't OTT. I find some websites tend to be too sensational and predict severe storms far too often.

Dave, pm me if a house ever comes up for sale in your street as you are always in the sweet spot, I really need to live there! 

[William Grimsley]

ECM precip chart for Thursday night, the storms part like the Red Sea as soon as they near here. It's so going to happen like that

 

Clipboard01.jpg

 

Crazy amounts of CAPE on Friday night in the SE, looks like big MCS imports and homegrown storms, could be severe

 

Look at that towards Rennes! Near -10 Lifted Index!

[Harry]

Look at that towards Rennes! Near -10 Lifted Index!

 

Ditto across the SE me ol' mucka!!

[Biggin]

Ditto across the SE me ol' mucka!!

I cant make out / see the outline of the UK on that Shouldve gone etc