Detailed Convective Discussion, Forecasts And Analysis

[BrickFielder]

Slight chance of a thunderstorm although conditions are not that good for most of the country stormwise. Prime area I think would be across the midlands moving eastwards during the afternoon.

The trouble is that there is not much of a trigger despite the moister pool of air across this area. I think we might be looking for orographic lift triggering across cornwall and wales.

There is not much in the way of wind shear although I do notice clouds are moving at a moderate pace today. The zero degree isotherm is still quite low so the risk of hail is high. A couple more charts.

Over all there is a chance of an isolated thunderstorm, probably down wind of the moors in the south west and the mountains of wales. Key area might be somewhere like Worcester to Wrexham in the afternoon or perhaps Reading late afternoon. Mostly I think it will just be heavy showers and many will see heavy showers passing either side of them. Biggest risk I think is from hail.

[Lauren]

Coast, do you have any recommendations on how i can understand the charts you post? Is there anything in simpleton language?

[Coast]

Coast, do you have any recommendations on how i can understand the charts you post? Is there anything in simpleton language?

If you have a look at one of the posts I made above I have put links to other information on the web that is applicable to each chart.

The best explanations for thunderstorm developments, charts etc are here:

There are some US based guides and quizzes here:

http://www.srh.noaa.gov/shv/?n=education-thunderstorms

Here are some key indices and what they mean:

http://www.skystef.be/storm-indices.htm

You need to check the NW learning area and specifically posts by John Holmes, Nick F and Brickfielder on this subject as I am only learning like you!

[knocker]

Coast, do you have any recommendations on how i can understand the charts you post? Is there anything in simpleton language?

I did post a guide to understanding some of the specific maps a couple of days ago if it's any help. But I suspect you have enough to be going on with. I believe it's known as information overload.

http://lightningwizard.estofex.org/ConvectiveWeatherMaps.pdf

[Lauren]

I did post a guide to understanding some of the specific maps a couple of days ago if it's any help. But I suspect you have enough to be going on with. I believe it's known as information overload.

http://lightningwiza...WeatherMaps.pdf

Ta for those links, I've got some reading to do!

[Stuart]

Head up For Thursday

Storm Forecast Issued: 2011-05-11 15:48:00

Valid: 2011-05-12 00:00:00 - 2011-05-12 23:59:00

Regions Affected

Scotland, NE England (remainder of Scotland, Northern Ireland and N England are included in the WATCH)

Synopsis

Lowering geopotential heights associated with an elongated area of low pressure to the north of Scotland (named "Norbert" by FU Berlin) will overspread Scotland during Thursday, whilst a relatively strong ridge of high pressure will persist across southern Britain.

Behind a northeastward moving occluded front, steepening lapse rates combined with surface heating will allow up to 600 J/kg CAPE to develop over north and northeast Scotland. Consequently scattered showers are expected with a reasonable chance of thunderstorms, particularly, but not exclusively, over NE Scotland with ELT's as low as -40°C. Showers may extend as far south as the south Midlands, but will be lighter in nature here.

Up to 30knots of low level shear combined with low LFC's (~300m) will promote the chance of a funnel or weak tornado to develop, primarily over C + E Scotland and NE England. Convective gusts of up to 40 knots is possible over C + S Scotland, with a chance of moderately-sized hail.

The majority of showers will decay after sunset, retreating to the coasts around Scotland.

http://www.ukasf.co.uk/module-Storm/mode-forecast/id-361/

[Coast]

Along with that UKASF forecast, NW has a forecast just out and both correspond with some of the other charts/sites:

[Stuart]

Before i got to bed I will update this for friday

Storm Forecast Issued: 2011-05-12 21:55:00

Valid: 2011-05-13 00:00:00 - 2011-05-13 23:59:00

Regions Affected

(Majority of the UK, excluding southern counties of England, are included in the WATCH)

Before i got to bed I will update this for friday

Synopsis

Lowering geopotential heights associated with an elongated area of low pressure to the north of Scotland (named "Norbert" by FU Berlin) will overspread Scotland, Northern Ireland and N England during Friday, whilst an increasingly-weak ridge of high pressure will persist across southern Britain.

Steepening lapse rates combined with surface heating will allow up to 400 J/kg CAPE to develop over Ireland and Northern Ireland in particular. Consequently scattered showers are expected with a low chance of thunderstorms, particularly, but not exclusively, over Ireland and Northern Ireland with ELT's as low as -30°C. Showers may extend as far south as the south coast, but will be lighter in nature here.

Up to 50knots of 0-6km shear combined with relatively low LFC's (~500m) will promote the chance of a funnel or weak tornado to develop, primarily over Ireland and N Wales/N Midlands. Hail will be common in many of the showers, with a chance of moderately-sized (locally borderline large) hail, particularly over Ireland and Northern Ireland.

Showers will persist well into the night, although the risk of thunder/lightning decreases significantly during the evening.

http://www.ukasf.co....orecast/id-362/

Edited May 12, 2011 by Stuart

[Coast]

ESTOFEX have a level 1 for parts of the UK today:

Storm Forecast

Valid: Fri 13 May 2011 06:00 to Sat 14 May 2011 06:00 UTC

Issued: Thu 12 May 2011 21:23

Forecaster: TUSCHY

A level 1 was issued for Ireland and UK mainly for large hail and an isolated tornado event.

SYNOPSIS

Another trough approaches Europe from the west with downstream ridging affecting most parts of south/central Europe. Focus for thunderstorm development will be a west-east aligned quasi-stationary boundary, running from the Bay of Biscay towards the Alps.

DISCUSSION

... United Kingdom and Ireland ...

A well mixed maritime air mass is present with low LCLs and daytime driven LL CAPE. Thunderstorms are forecast despite uncertainty of final coverage. SBCAPE of 200 - 500 J/kg and cold EL temperatures (mainly over Ireland) indicate a chance for a few deep updrafts within a strong sheared environment (0-6 km bulk shear of roughly 20 m/s). Hence, a few better organized thunderstorms with isolated large hail and strong wind gusts are well possible, next to an isolated tornado event. Despite no real indications of supportive BL helicity/shear, any deviant storm motion may result in good helical flow, given strength of background wind field.

SkyWarn and TORRO currently have no forecast for convective activity, here is what others show:

I'm not quite sure where the level 1 comes form at this point, but NE Scotland does seem to be highlighted for today

[Stuart]

here ukasf Storm Forecast for sat

Storm Forecast Issued: 2011-05-13 17:08:00

Valid: 2011-05-14 00:00:00 - 2011-05-14 23:59:00

Regions Affected

NE England, E Midlands, E Anglia, SE England (N + E Scotland, Northern Ireland, Wales and most of England is included in the WATCH)

Synopsis

Cold air aloft and lowering geopotential heights associated with an elongated area of low pressure to the north and east of Scotland (named "Norbert" by FU Berlin) will overspread much of the country during Saturday, whilst ridging continues to build from the southwest.

Steepening lapse rates combined with surface heating will allow up to 500 J/kg CAPE to develop over eastern counties of England in particular. Consequently scattered showers are expected quite widely with a few thunderstorms, particularly, but not exclusively, over eastern and southeastern England with ELT's as low as -30°C.

Deep layer shear looks particularly meagre at <20knots, although an increase from the west during the day (up to 50knots 1-6km with 25knots 0-1km) combined with low LCL's (~200m) may allow for a funnel or weak tornado across Northern Ireland initially, this risk extending across to Wales/N England by evening. Hail will be common in many of the showers, with a chance of moderately-sized hail, particularly over eastern counties of England. Large rainfall accumulations may fall in a short space of time locally.

Ridging from the SW will cause showers to decay here, although such showers will continue across eastern England during the first part of the evening before eventually decaying.

http://ukasf.co.uk/m...orecast/id-363/

Edited May 13, 2011 by Stuart

[Coast]

Great stuff from UKASF for the East from Essex to Yorkshire! Here's what ESTOFEX have:

Storm Forecast

Valid: Sat 14 May 2011 06:00 to Sun 15 May 2011 06:00 UTC

Issued: Sat 14 May 2011 05:25

Forecaster: VAN DER VELDE

A level 1 was issued for parts of Portugal, Spain and the Alpine region mainly for large hail.

SYNOPSIS

The dominant system of interest on the map is a strong cold front, most pronounced at mid levels. It belongs to a depression near southern Norway and is pushed by a steady northwesterly flow into western Europe. Atlantic high pressure is strong and builds behind the cold front. A jetstream runs parallel over the frontal region and creates 15-25 m/s deep layer shear in the region with typically 500 J/kg MLCAPE in most areas before the front. Almost everywhere along the front CAPE density is actually predicted weaker in the mixed phase region than at lower levels.

DISCUSSION

...southern/eastern France...

At the moment storms are ongoing over southern France in GFS-indicated strong mid level cold air advection area. As more surface-based CAPE becomes available during the day, storms can profit better from the shear, but shear is aligned with the frontal convergence zone and this provokes more linear convection than isolated cells. The most curvature in the hodographs is found over (north)eastern France, where SREH is also calculated to be more than 250 m²/s². However, the poor shear angle might destroy the environment, where LCL is also calculated to be low, yielding too much warm-cloud water content. So large hail seems only marginally possible. Near the Alps, upslope moisture lifting combined with convection could result in flash floods.

SkyWarn uk and TORRO currently have no forecast or warning, the Netweather forecast is here:

http://www.netweather.tv/index.cgi?action=convective;sess=

Charts and models:

Although CAPE and dewpoints don't look up to it according to RASP charts:

'Nice' looking tornado potential down the eastern side of the country this afternoon:

[P-M]

Hi, Been a while since I posted but thought I would check in..... I hear a few people mentioning (as the post above) the storm risk from Essex to Yorkshire, but the Northeast of England and also parts of Southern Scotland are highlighted in the Thunderstorm watch for UKASF.... I am confused can someone help me out and let me know if the Northeast i.e Tyne and Wear and Northumberland are actually included in the watch? Cheers

[Guest Kent-Weather]

SkyWarn-UK I doubt will have any watches issued as it's not an overall day for anything that may concern other then hail

[Guest Kent-Weather]

This could be a great thread during spring and summer if more members had a go at discussing or forecasting (obviously in substantially more detail than would otherwise be the case in the 'Convective Chat' thread) ahead of convective or severe convective storm risk days. Currently this feels like a "watered down" thread, with very little of what I believed to be its purpose taking place.

So let's make it one Naturally it's going to very quiet when there's not much activity around but the more technical discussions can go on in here and leave the general chat to the general thread. Only problem being that you can only fit so much of a technical chat in once theres technical details to discuss such as the latest model outputs. Otherwise your speaking in more general terms, hence the other thread being so immensely popular I guess?

Note: I dont wish for this post to sound like I'm excluding ANYONE from this thread, very far from it indeed. Hopefully everyone will understand my meaning without causing any offence or backlash.

[Coast]

Doesn't look like there's much forecasting and analysis taking place in here, just copies of other sites' forecasts and weather charts. The charts, by the way, can be resized to much smaller thumbnails, and the charts from the LightningWizard in particular can be found simply by visiting the site, the link to which has already been posted in the thread.

Of course they can, but as the charts I add are hot-linked that's the size the forum software reduces them to. You are quite right, anybody can go to the source of the charts and forecasts but what I post is a round-up of what many current sources are showing so you can compare and contrast in one location on here.

I'm all for everyone getting involved in this particular thread and if you want to have a go at forecasting/guessing events or areas where you think convective activity may appear, no one is going to shoot you down for having a look and trying!!! :lol:

So let's make it one

Absolutely!!!

More contributions please!

[A.J]

Robin, don't you dare re-size or stop posting your convective hot links!...You've been posting them for a couple of years now, and yes, at first, I could've throttled you for them taking up 100 page scrolls...lol...but I'm used to them, indeed they are now part of the British constitution, like say, sliced bread! Long live the hot links!.......Right, that's enough caffeine for me this morning, me thinks! :lol:

Edited May 15, 2011 by ajpoolshark

[A.J]

But why, AJ? Do we really need to be spoon-fed data from across the internet? Admittedly, I myself post up charts from LightningWizard and Weather Online, but they are accompanied by substantial discussion concerning their relevance to the storm risk day in question. Otherwise they are just charts on a screen.

The way I see it is that this site is Netweather. Not UKASF; not ESTOFEX; not UKWW, etc. Posting these sites' forecasts or discussions in this thread leaves very little (if any) input to add from members here. Dare I say, it almost comes across as if some on this forum regard the members/forecasters on these sites as being more "in the know" about convective weather than anyone on here. Simply put, I don't think said sites' forecasts should be posted in this thread. That's my opinion.

You missed the humour, my post was actually made in a light hearted mood, never mind!................... ....Storms are probably the most difficult meteorological phenonema to forecast, so quoting different forecasts from different entities is no big issue IMO, in fact it can aid discussion, with members analysing and dissecting the different forecasts, this IMO needs to be encouraged as it's this thats missing from this particular thread, it's kind of pointless for members to post charts then give no analysis, as it means that the information contained in such charts is totally lost on quite a number of members.......However, on the flip side, one thing to note though is remembering what the actual purpose of this thread is ..If the purpose is to give an accurate detailed analysis of convective potential then would be best to leave it to the experts?..Nick & Brickfielder & a few others give expert analysis on this thread when convective potential warrants it......From my perspective, I'd take Nick's & BF's forecasts over UKASF & Estofex any day of the week!

[Osbourne One-Nil]

Perhaps if you'd like a more constructive thread, the way forward is to contribute in a constructive way rather than tell everyone else what they're doing wrong? Feel free to use the feedback section of the forum, but I have to say right now you're posts are proving a bit counterproductive! As for Nick F and Brickfielder, they're members of the forecast team for a good reason and whilst you may not consider them experts, most people would, and they're up there on merit.

Back on topic now please!

[Nick F]

Unfortunately I haven't had as much time as I would have liked recently to contribute to this thread , but I have been doing convective/storm forecasts as often as I can /when warranted, they can be found here:

http://www.netweather.tv/index.cgi?action=convective;sess=

I don't consider myself as an expert in the sense of being a professionally trained meteorologist and I don't have a total grasp of physics of the atmosphere that professionals may have. But I like to feel, through experience of chasing storms in the US and much background reading, that I have a reasoaable grasp of what's going on in the atmosphere to create the conditions that lead to storms and severe storms and I hope that comes over in my forecasts for netweather.

As for the charts posted by Coast, yes they are very useful to get a snapshot of what's going and there needn't be an 'expert' explanation/analysis to go with them, though it does take a while to scroll through them when they're not thumbnailed! :lol:

[Stuart]

Storm Forecast Issued: 2011-05-24 21:14:00

Valid: 2011-05-25 00:00:00 - 2011-05-25 23:59:00

Regions Affected

(W Scotland, Northern Ireland and N + W Ireland are included in the WATCH)

Synopsis

Relatively deep, cut-off Low pressure "Viktor" (FU Berlin) will approach the northwest of the country from the Atlantic during Wednesday. Lowering geopotential heights associated with low will overspread Northern Ireland and western Scotland late in the day during Monday, whilst ridging continues to hold across the southern and eastern Britain.

Behind the cold front, steepening lapse rates combined will allow up to 250 J/kg CAPE to develop, with numerous showers forecast to affect W Ireland, Northern Ireland and W Scotland late in the afternoon, throught the evening and overnight. The risk of isolated thunder/lightning will continue into the night, the majority of which is expected to be along the coastline and/or offshore, with ELT's as low as -35°C.

Deep layer shear over the areas of interest is quite meagre once the cold front has passed, at around 20knots, although this combined with low LCL's (~200m) may allow for a funnel to develop. Some small hail is possible in some of the showers.

http://www.ukasf.co....orecast/id-366/

sorry the map update not working for me

Edited May 25, 2011 by Coast
It is now!!!

[Coast]

Confirmed by some others:

[Stuart]

Storm Forecast Issued: 2011-05-25 23:26:00

Valid: 2011-05-26 00:00:00 - 2011-05-26 23:59:00

Regions Affected

NE England, East Midlands & East Anglia (England, Wales, Northern Ireland & S Scotland included in the WATCH)

Synopsis

Cut-off Low pressure "Viktor" (FU Berlin) continues to slowly migrate eastwards across the British Isles during Thursday. Lowering geopotential heights associated with low will overspread much of the country, whilst heights slowly rise across Ireland and SW England during the day.

Steepening lapse rates combined will allow up to 600 J/kg CAPE to develop, with widespread showers and local thunderstorms over England and Wales in particular, whilst frontal rain will continue to affect parts of Scotland, with ELT's as low as -40°C.

Deep layer shear over the areas of interest of 20knots combined with low LCL's (~200m) may allow a funnel or weak tornado to develop, most likely over the Midlands/East Anglia. Some small hail is likely in many of the showers, locally moderate in size over Northern England.

Extensive cloud, however, and very moist profiles may hinder the potential for thunder/lightning and/or hail. As ridging builds from the southwest such showers should gradually decay, although are likely to linger across eastern counties until late in the evening

http://www.ukasf.co.uk/module-Storm/mode-forecast/id-367/

[Supacell]

Its been a while since I have done this but here goes.

Good chance of some scattered thundery showers and storms today across eastern areas with, I feel, gusty winds and hail a risk in any larger showers or storms. A decent amount of CAPE and negative LI for eastern counties. The chart shows this for when I reckon peak time will be.

An area of wind convergence sets up in the afternoon in areas around East Yorkshire up the A1.

Wind Shear is definitely better further south and therefore any storms here have the potential to develop into multi cells. Further north I think pulse type storms more likely.

Unfortunately cloud cover may hamper convection a bit but will have to wait and see.

EDIT: Met Office Invent puts best action across the East Midlands this afternoon.

Edited May 26, 2011 by Supacell

[BrickFielder]

Today could well be a bust as far as storms are concerned especially considering the cloud cover and the fact that we have a fairly cold air feed.For me there are three areas of interest. Firstly the occlusion currently crossing the midlands may pep up as it crosses Lincolnshire from around mid day.

The forecast skewT shows it is possible but the air is moist all the way up.

The next area to consider is the north east coast and here I am not convinced, the forecast skewT is not that promising. Both mixed layer and suface based cape are better but I do wonder how deep that instability is.

The third area is from an area from oxford through to the east midlands from mid afternoon onwards. By this time the mid level lapse rates are begining to reduce.

However there is a chance of the cloud brekaing up a little with some daytime heating helping.

I also like the fact that it is under the left exit of a jet streak with some divergence aloft.

Forecast SkewT's suggest there is a window of opportunity, which disappears late afternoon.

Will any of these storms come off? I am not sure. The relatively cold air feed means instability will not be that great. Models don't appear to agree on moisture levels and there is not much in the way of clear skies on the satelitte pictures.

Prime risk would be hail, low level shear is enough for tornados but updraft strenghts probably will not be strong enough to aid formation. An isolated one cannot be ruled out of course. Supercells seem unlikely to me due to the lack of wind shear through the mid levels.

Some final vorticity charts which back up my thinking (note the 500hpa vorticity charts are somewhat different)

(higher Absolute vorticity can suggest potential for air to lift).

If you still non the wiser on whether we will get storms or not, then you are not alone.

[BrickFielder]

Some positive and some negative signs for storms tomorrow. As usual it is still al little early to put much meat on the bones. First lets talk about some of the negative factors and first up is mid lavel lapse rates.

If you generally consider 26 degress diffrence between 850hpa and 500hpa to be the minimum lapse rate for storms to develop then most of the UK will not see storms. Next up is a forecast SkewT for Wrexham which shows cloud bases will not be that low and cloud tops will be lower than you would generally expect for a thunder storm.

Looking at the very upper winds (300hpa) we don't really see much in the way of divergence aloft.

Despite all indications that we will at best see some heavy showers rather than thunderstorms there are some factors which interest me. First up in the deep layer wind shear, which is relatively high in places.

That sort of shows there is the possibility of rotating cells. While this would suggest tornadoes are possible the poor low level shear, weak instability and high cloud base puts a severe limit on the potential (read very low probability).

The mid and upper level humidity charts kind of interest me as well because there is a very stark contrast here.

Most interesting of all are the following charts.

The first gives hints about general lift and subsidence of air and suggests lifting over parts of northern England. The second shows a mid level jet streak approaching from the south.

Of course all this can change before tomorrow so we will need to wait and see, with the indicators for storms being rather weak at the moment.