Convective/Storm Discussion early to mid June (merged)

[grab my graupel]

Nice satellite image this afternoon

[suffolkboy_]

Here is the 24 hour cumulative rainfall. Looks like most of the heavy stuff only brushed the coastline:

Well I am right under the red part on that map, however i've only see 8mm, i think as these were high level storms, alot was evaporated again before it reached the ground.

[PB22]

Well it was an exciting morning here in eastern Suffolk, with a lot of rain this morning and plenty of thunder and lightning. I ended up with 27mm here at home, but at work, nearer the coast still, they had 33mm, with lots of thunder and lightning.

The wind turbine at Lowestoft copped an unfortunate one, when it got hit by lightning earlier today.

http://news.bbc.co.uk/1/hi/england/suffolk/6733827.stm

[BrickFielder]

Where the UKMO mesoscale model did well yesterday I don't think 0Z models for either GFS or UKMO performed that well. MCS over east anglia pushed north quicker than forecast because low pressure of the west coast of Spain and Portugal is moving quicker east and north pushing things northwards.

This is likely to push the upper level low current south of cornwall more northwards with a result that upper levels and more importantly temperatures at 700hPa should relax more over southern England.

I think we could be looking at an isolated thunderstorms this afternoon across southern England.

Indications are at the moment that the ingredients for a severe thundestorm may not quite come together and alot will depend on clearing skies with temperatures reaching high enogh to break the Cap. 12Z soundings what there are of them suggest that 25C might be needed to break the Cap.

There might be some low level wind convergence across the south.

I am struck by how much directional wind shear there could be over Kent later in the day.

Forecast SkewT for Salisbury shows it is just about possible for storms to develop late on.

I am just not quite sure it will all come togather at the moment.

[suffolkboy_]

--><div class='quotetop'>QUOTE(Paul B @ 8 Jun 2007, 02:56 PM) <{POST_SNAPBACK}></div><div class='quotemain'><!--quotec-->Well it was an exciting morning here in eastern Suffolk, with a lot of rain this morning and plenty of thunder and lightning. I ended up with 27mm here at home, but at work, nearer the coast still, they had 33mm, with lots of thunder and lightning.

The wind turbine at Lowestoft copped an unfortunate one, when it got hit by lightning earlier today.

http://news.bbc.co.uk/1/hi/england/suffolk/6733827.stm

[Lightning Hunter]

Well we reached just below 25°C an hour ago, but the sea breeze has kicked in a nd put it back to 21°C.

No signs of any build up, just some Ac and very shallow Cu well inland.

[PB22]

--><div class='quotetop'>QUOTE(Paul B @ 8 Jun 2007, 02:56 PM) <{POST_SNAPBACK}></div><div class='quotemain'><!--quotec-->Well it was an exciting morning here in eastern Suffolk, with a lot of rain this morning and plenty of thunder and lightning. I ended up with 27mm here at home, but at work, nearer the coast still, they had 33mm, with lots of thunder and lightning.

The wind turbine at Lowestoft copped an unfortunate one, when it got hit by lightning earlier today.

http://news.bbc.co.uk/1/hi/england/suffolk/6733827.stm

Where abouts in Suffolk are you? According to the NetWeather Radar I got over 40mm, but I actually only got 8mm. The rain wasn't torrential by any means, my heaviest rainfall was 5.6mm/hr to be precisewhich is only in the heavy catagory.

I'm up the coast, not far from the Sizewell power stations. It seems places east of the A12 up to Lowestoft saw the most rain. Was heavy rain here for 4-5 hours this morning.

[*Stormforce~beka*]

Well we reached just below 25°C an hour ago, but the sea breeze has kicked in a nd put it back to 21°C.

No signs of any build up, just some Ac and very shallow Cu well inland.

Heya. Definately very close! It touched 24.3 an hour or so again and i saw a little tower shoot up but soon came back down as cloud came along and the temp dropped. Its now 23.9 so its defiantely touch and go. Its only got the next hour or so to do the job!!

[johnholmes]

a number of very valid comments about the radar, that is ANY radar apparently overdoing the rainfall intensity compared to what has been recorded in some places.

With rain/thunderstorms, from middle level this has always been the 'Achilles' heel of radar rainfall predictions.

Yes, as someone has already mentioned, evaporation between the level at which its falling from, the angle the radar is at, and the amount thus reaching the ground all play a part.

Its very very accurate for rainfall that is falling below about 9-10000ft but above that much less so.

All one has to do is be aware of that problem and try and adjust to what to expect.

Its a long time since I was involved on the forecast side so how the various computers deal with this situation I am not sure, better I would have thought as they all have the various parameters at each level from the surface up to 300mb(30,000ft) or so their prediction should be fairly accurate. That is assuming they get the rainfall in the correct place. GFS largely did not in this case whilst the Met O model did so, albeit too much overall.

hope that helps understand the limitations of radar in certain circumstances.

[Joneseye]

Thanks for that John a useful explanation and something that is maybe worth pinning.

[kold weather]

Interesting post John, though I think your not being very fair to the GFS. It was probably just as close as the UKMO model was, the UKMO placed the main area of rain a little too far west while the GFS was equally a touch too far east. In terms of timings of the system and afternoon forecast the GFS nailed it to perfection and aced the UKMO model, which according to its run yesterday the SE is still meant to have another 6hrs of rainfall!

Meanwhile the GFS always forecasted the main lobe of rainfall to move out into the North-sea between 12-3pm, a good 6hrs more accurate then the UKMO...yes this is probably petty on the grand scale of things, esp given the convective nature of the system but based on yesterdays 12z runs the GFS did a touch better then the UKMO.

[johnholmes]

we agree to differ a touch KW but its of no importance. Be interesting to read TWS's interpretation when it comes in.

[Thundersquall]

Some cumulus clouds are building-up over Bristol at the moment. Nothing spectacular but maybe

there could be something happening later.

A few dots of blue are appearing here and there over Southern England.

http://www.metoffice.gov.uk/weather/uk/radar/

[Lightning Hunter]

Any convection long since died away here now, just a barely distinguishable milky white haze of altostratus now.

21.3°C after a high of 25.1°C.

[Pixlet]

Very large Cumulonimbus building outside, very defined, i'd take a photo but i'm worried the reprobates outside will think i'm nuts taking photos of clouds.

This is looking directly south from postcode area GU35.

[*Stormforce~beka*]

Ooooh that sounds promising!! Ah I see where you are (sorta) - Go take the picture never mind the chavs!

[Karen Ann]

There's been huge towers building here this afternoon to my North and North West mainly, which if past experience is anything to go by, could mean a storm for the Warminster/Westbury area later. There are some now, to the SW of me so maybe I'll be in luck. I shall be watching and listening with a nice cool beer anyway.

[*Stormforce~beka*]

Ah thats more like it! Storms to the west - storms to the east and me in the middle!!

[chapmanslade]

There's been huge towers building here this afternoon to my North and North West mainly, which if past experience is anything to go by, could mean a storm for the Warminster/Westbury area later. There are some now, to the SW of me so maybe I'll be in luck. I shall be watching and listening with a nice cool beer anyway.

Certainly plenty of convection to the south along what I believe is a weak wind convergence zone. There is a slight northerly airflow at the surface here that is meeting the sea breeze to the south of us. It just doesn't quite look enough from where I am though.

[Andy Bown]

Where the UKMO mesoscale model did well yesterday I don't think 0Z Forecast SkewT for Salisbury shows it is just about possible for storms to develop late on.

There's been huge towers building here this afternoon to my North and North West mainly, which if past experience is anything to go by, could mean a storm for the Warminster/Westbury area later.

Certainly plenty of convection to the south along what I believe is a weak wind convergence zone. There is a slight northerly airflow at the surface here that is meeting the sea breeze to the south of us. It just doesn't quite look enough from where I am though.

It looked very promising around 18.00 with a great area of TCu building around Westbury, however it died away. Now it is very hazy, one of those evenings where seeing cloud size/shape is difficult.

Chapmanslade has a better view to the South than myself.

[AcceptedPlanet]

A few black clouds forming over Bristol, seems to getting very muggy

[Andy Bown]

Oh hello, some showers popping up over Hampshire/Dorset/South Wiltshire on the last few slides of the NW Extra radar. Meteocentre showing a CB on the South coast at 20.00.

Edit - and Gloucestershire.

[Supacell]

Travelled out to meet the storms in the SE and the bl**dy things turned and ran the other way out to sea.

I therefore want to apologise to all those in Norfolk and Lincolnshire that were expecting something today, i believe i may have scared them off.

Whens the next lot of storms going to arrive then?

[Pixlet]

I noticed the one near Dorset, what direction are these expected to move in?

Oh hello, some showers popping up over Hampshire/Dorset/South Wiltshire on the last few slides of the NW Extra radar. Meteocentre showing a CB on the South coast at 20.00.

Edit - and Gloucestershire.

[Andy Bown]

Wow!

If you have access to the 5 min radar, zoom in on the showers over Gloucestershire and watch them develop from the 21.30 slide to the 21.45 slide. That is rapid development and up to about 50mm per hour rain rate just N|orth of the M4! Those over Dorset/Hampshire aren't so heavy but it seems something has 'clicked' in the atmosphere about 30 miles to my North and 30 miles to my South !

Edit - Pixlet - unsure as they've only just formed. Low level movement is slow NE-SW but they'll be governed by upper winds.