Detailed Convective Discussion, Forecasts And Analysis

[Paul]

Please use this thread for more detailed posts about the upcoming storm / convective weather risk.

The general discussion and chat thread can be found here:

[Coast]

The weekend seems to start out with a big swathe of possibility across the UK:

Late Friday night through to Saturday night look encouraging lower down the country:

[Coast]

So what are the possibilities on what could turn out to be a busy weekend convection-wise?

Here's a recap on what ESTOFEX have to say for today:

Storm Forecast

Valid: Fri 06 May 2011 06:00 to Sat 07 May 2011 06:00 UTC

Issued: Thu 05 May 2011 12:31

Forecaster: TUSCHY

A level 1 was issued for Portugal and Spain mainly for large hail and severe wind gusts. An isolated significant hail event can't be ruled out over south-central Spain, e.g. Madrid southwards.

A level 1 was issued for NW-France mainly for large hail and an isolated severe wind gust/tornado risk.

A level 1 was issued for S-Turkey mainly for flash flood producing thunderstorms.

SYNOPSIS

CAA continues over east-central/east Europe with a quasi-stationary longwave trough still in place. Strengthening ridging over central Europe further assists in the advection of a well mixed, dry and cool air mass far to the south, even affecting parts of the central/eastern Mediterranean with negative surface dewpoints. A north-south aligned air mass boundary has established to the east of that feature and attendant surface high pressure are with a sharpening moisture gradient present over far eastern Ukraine and parts of Russia.

Over the far northeastern Atlantic, an extensive deep cyclonic vortex is anchored with little eastward movement forecast. However, a significant impulse along its southwestern fringe is about to assist in the development of a sharp mid-/upper trough with a much shorter wavelength. This feature circles around the southern part of the main vortex and approaches Portugal as a significant vorticity lobe from the west during the night hours. Brisk SW-erly flow covers regions from the Iberian Peninsula all the way to UK, atop gradually moistening LL. Hence, a more widespread thunderstorm risk is in store for the upcoming forecast period.

Stable conditions persist beneath increasingly tilted high pressure/ridge features over central Europe.

Models agree reasonably well with the main pattern, revealing some discrepancies within the BL qualitiy...especially over NW-France.

DISCUSSION

... W-France ...

Models still diverge regarding the final BL moisture content. ECMWF and GFS all indicate an ongoing moisture advection regime during the forecast with dewpoints increasing to 10°C and more. GFS remains very bullish, developing sfc. dewpoints in the upper tens all the way to the W-English Channel with ECMWF showing a modest solution. Nevertheless, all models indicate modest MLCAPE of at least 500 J/kg, probably maximized over NW-France during the afternoon. Shear remains weaker compared to Spain, but roughly 15 m/s DLS and somewhat enhanced SRH-3 indicate a large hail risk with stronger thunderstorms, next to isolated severe wind gusts. Also, LCLs around 1000 m and somewhat enhanced LL shear may also cause an isolated tornado event. As thunderstorms spread to the N/NE during the night, decoupling from the BL results in a mainly elevated thunderstorm risk over SW-UK. Despite an isolated marginal hail risk, no severe is forecast.

SkyWarn UK have:

Severe Weather Risk - Low

A soaking band of rain spreading east slowly, with locally heavy showers most of the UK into the weekend. Thunderstorms becoming stronger Saturday turning to persistent heavy rain overnight.

No current Watch or Warning in effect.

UKASF and TORRO currently have nothing, Meteoalarm have a large part of Western France highlighted for a yellow alert, but no description or forecast.

Hers are some charts:

Looks like the Brest Peninsula in France is the one to keep an eye on this afternoon with something possibly moving into the South West later in the afternoon and early evening. Not sure if it will get up into Dorset or Hants during daylight hours.

[Coast]

Forecast soundings for today/tomorrow:

This afternoon at Heathrow:

Birmingham:

Plymouth:

Tomorrow afternoon at Heathrow:

Birmingham:

Plymouth:

Seems to be looking better away from the South Coast currently

[Paul]

In depth convective outlook:

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

[knocker]

It has crossed my mind that there may be a few members out here, who like myself, are not completely au fait with using the myriad of convective weather maps that can be used a s a forecasting tool., some of which are posted on here. This makes it difficult, not to say presumptious , to contribute in any useful way to any to technical convection discussion.

Something I have found very useful in this respect is a guide to using Convective Weather Maps by Oscar van der Velde that is available on the web at:

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

It's distinctly possible that this has been posted before so please ignore if that is the case.

[johnholmes]

I think you would find this link very helpful Fred, or anyone else perhaps struggling with the complications of trying to predict storms and their severity.

done by Nick, Senior Forecaster for Net Wx-recommended.

http://forum.netweather.tv/topic/29496-guide-to-uk-thunderstorms-setups/

All or almost all the various parameters mentioned when dealing with storms derive from the basic 3 dimensional chart, known on the web usually as skew-t, others may know it as t-phi, Fred you dealt with these every day?

A read through this, okay it still has some missing bits in it that I will eventually get round to correcting, but it goes SLOWLY into the detail of what one can see on the skew-t. Down the right hand side, if you use, the Wyoming data sets, it explains about CAPE etc etc, the link to basic skew-t is below

http://forum.netweather.tv/topic/16002-a-simple-guide-to-understanding-skew-t-diagrams/

I'm sure Nick would be happy to explain anything, I am happy to do so via pm, although I'm not one that uses the terms of CAPE etc preferring to use forecast experience of how to interpret the skew-t.

[knocker]

Thanks for that John. I had a quick read of Nick's post earlier but haven't had a chance to read it properly as yet.

I don't have a problem with the t-phi or skew-t (prefer the t-phi. Wouldn't mind a pound for everyone I've plotted)and the use of but I realised that the convective maps were a different matter although they originate from the basics. Anyway mustn't get carried away or I'll forget I'm retired.

[knocker]

Having had a perusal of the charts in my new role as a self-appointed expert my tentative conclusion is that there will probably be outbreaks of thundery activity in some areas this morning but the main activity will be be this evening and tonight particularly in southern, central and western areas. The former associated with convective activity spreading north from France and the latter with rain, perhaps thundery from the west associated with the front?

Edited May 7, 2011 by weather ship

[Coast]

I'm afraid here comes another deluge of charts to see who is saying what about today's potential:

Here is what ESTOFEX (European Storm Forecast Experiment)have to say:

Storm Forecast

Valid: Sat 07 May 2011 06:00 to Sun 08 May 2011 06:00 UTC

Issued: Sat 07 May 2011 05:35

Forecaster: VAN DER VELDE

A level 1 was issued for UK and western France mainly for some chance of tornadoes.

A level 1 was issued for eastern Spain mainly for some chance of tornadoes, large hail, and excessive rain.

A level 1 was issued for northern Algeria mainly for large hail.

SYNOPSIS

A large low pressure area centered west of Ireland covers Iberian peninsula, France, British isles and Benelux. A warm and unstable airmass extends northward beyond Scotland with here and there embedded thunderstorms. A satellite upper shortwave trough swings over southeastern Spain, Balearic islands, and southern Mediterranean Sea and has an associated strong dynamic tropopause anomaly and QG lifting signature. Another major low is situated over Romania and surroundings, with the strongest lifting and instability on its south side.

DISCUSSION

...UK and western France...

While some areas will be capped, cloudy, or having only elevated CAPE, some parcels will likely be rooted in the boundary layer and experience quite reasonable vertical shear and helicity values. GFS predicts about 20 m/s 0-6km shear vectors, 200 m²/s² 0-3 km SREH and in the central UK around 12 m/s 0-1 km shear, which combined with a few hundred J/kg CAPE and mixed layer LCLs of 600-800 m hints at a chance of tornadogenesis. Two PV maxima pass over the southern UK with ascending motions, during morning and evening. During the evening pass the shear conditions seems best and there is a significant wind maximum near the dynamic tropopause level. As LCLs and CAPE are low, large hail isn't as likely, but cannot be ruled out given the chance of mesocyclones.

Here is what SkyWarn UK have to say:

Last Update: 1400UTC, Friday 6th May 2011

SKYWARN UK SEVERE THUNDERSTORM WATCH #025

ISSUED: 1400UTC, FRIDAY 6TH MAY 2011

SKYWARN UK HAS ISSUED A SEVERE THUNDERSTORM WATCH FOR THE FOLLOWING REGIONS:

NORTHERN IRELAND SOUTHWEST ENGLAND SOUTHERN ENGLAND WALES MIDLANDS NORTHERN ENGLAND SCOTLAND

IN EFFECT FROM 1400UTC FRIDAY 6TH MAY UNTIL 2300UTC ON SATURDAY 7TH MAY 2011.

UNSTABLE WARM AIR ADVECTING NORTH IN THE VICINTY OF THE COLD FRONT

THERE IS A POSSIBILITY OF SEVERE THUNDERSTORMS AFFECTING THE INDICATED REGIONS IN THE TIME PERIOD SPECIFIED. THREATS WITHIN THIS WATCH INCLUDE, BUT ARE NOT LIMITED TO:

HEAVY RAIN...HAIL...LIGHTNING...STRONG GUSTS...TORNADOES

DISCUSSION:

USING A BLEND OF GLOBAL AND REGIONAL HIGH RESOLUTION MODELS, THERE IS STRONG CONFIDENCE OF A POTENTIALLY SEVERE CONVECTIVE SCENARIO SPREADING NORTHWARD FROM FRIDAY. ON FRIDAY AFTERNOON, POST-FRONTAL CONVECTION ACROSS EIRE AND NORTHERN IRELAND MAY BE STRENGTHENED BY UPPER SHORTWAVING AND AN ORGANISING SHEAR PROFILE. LOW LAYER SHEAR IS SUFFICIENT FOR A POSSIBLE TORNADO RISK HERE. LATE FRIDAY AN ELEVATED UNSTABLE AIRMASS ARRIVES INTO THE SOUTH COAST AND SOUTHWEST OF ENGLAND ADVECTING NORTHWARD WHILE SPREADING EASTWARD ACROSS THE MIDLANDS. THERE EXISTS A MODERATE HAIL RISK WITHIN THIS CLUSTER OF STORMS. SATURDAY LATE MORNING ONWARDS CONVECTION WILL INITIATE WALES AND MIDLANDS AS THE UPPER JET TAKES EFFECT FROM THE SOUTH, THIS WILL BE ONGOING THROUGH THE DAY BUT FURTHER NORTH MATURE CELLS MAY BECOME STRONGER WITHIN A SHEAR PROFILE FAVOURABLE FOR STRONG GUSTS AND POSSIBILITIES FOR TORNADOES. LATE SATURDAY STRONG STORMS MAY ADVECT INTO THE SOUTHWEST AND SOUTH COAST CONTINUING NORTHWARD AS THE RENEWED COLD FRONT APPROACHES.

Here is the current TORRO (Tornado and Storm Research Organisation) forecast which will be updated during the day:

TORRO CONVECTIVE DISCUSSION 2011/006

A TORRO CONVECTIVE DISCUSSION has been issued at 1830GMT on Friday May 6 2011

Valid from/until: 1830GMT-0900GMT on Friday May 6/Saturday May 7 2011 for the following regions

Parts of (see map) Much of England Much of Wales Southern Scotland

THREATS

Wind gusts to 50mph; isolated hail to 2-3cm; frequent lightning; isolated tornadoes this evening in N England.

Plume of high theta e/w air is moving northwards into south-western parts of England. Upper trough along with warm advection in the lower levels has allowed thunderstorms to develop along the warm front across south-western parts. These will move NNE and N, with further development likely within the plume overnight. Other storms have formed over the higher ground of N Wales.

The storms will generally be elevated above a cool boundary layer overnight. Cloud-layer shear is fairly weak, meaning elevated mesocyclones are unlikely. However, reasonably stout updraughts are likely at times, and with reasonable CAPE in the mid-layers, severe hail may accompany the stronger cores. In addition, with 40 knots of flow at 850mb for a time, locally strong-marginally severe wind gusts are possible. However, the overall risk of organised severe thunderstorms seems fairly low, hence a WATCH is unlikely to be issued - even so, some organised strong thunderstorms are likely.

Storms developing across N England early this evening are surface-based, and have a short window in which they may produce an isolated tornado before they become elevated.

Later in the night, another trough will approach southern parts with a second area of showers and thunderstorms accompanying it. These will move northwards through Saturday. Surface-based storms are possible in places tomorrow, especially in central and northern parts. However, the overnight evolution and eventually distribution of convective cloud debris tomorrow morning means that defining risk areas is not possible at this time. Should surface based storms develop tomorrow, shear/instability profiles look sufficient for supercells with a large hail/damaging wind risk, along with isolated tornadoes. Further discussions and possible watches are likely.

This is the USAF's 21st Operation Weather Squadrons advice to European fighter and bomber squadrons on the possibility of thunderstorms later today:

This is their interpretation of the advice from our own Met Office on the possibility of thunderstorms:

This one is the NOAA's National Weather Service Aviation Weather Centre Mid Level significant weather chart for the aviation industry giving their expectation of activity:

Here is the RASP data (Regional Atmospheric Soaring Prediction) for glider pilots etc:

Convective Available Potential Energy indicates the atmospheric stability affecting deep convective cloud formation above the boudnry layer. A higher value indicates greater potential instability, larger updraft velocities within deep convective clouds, and greater potential for thunderstorm development (since a trigger is needed to release that potential). Note that thunderstorms may develop in regions of high CAPE and then get transported downwind to regions of lower CAPE. Also, locations where both convergence and CAPE values are high can be subject to explosive thunderstorm development.

The dew point temperature at a height of 2m above ground level. This can be compared to observed surface dew point temperatures as an indication of model simulation accuracy; e.g. if observed surface dew point temperatures are significantly below those forecast, then BL cloud formation will be poorer than forecast.

Heat transferred into the atmosphere due to solar heating of the ground, creating thermals. This parameter is an important determinant of thermal strength (as is the BL depth).

KO Index = blue lines with values. (S = >+6 = stable, L = < -6 = unstable).

Vertical motion forced by dynamical forcing at 500 hPa = zones in color (hPa/hour).

Critical values KO.

> 6: no potential risk thunderstorms.

2-6: small potential risk for thunderstorms.

< 2: potential risk for thunderstorms.

Convective clouds = grey lines with values in %.

Soaring-Index = values in color (in deg Kelvin)

Some critical values for the Soaring Index.

15-20: isolated showers, 20% risk for thunderstorms

20-25: occasionally showers, 20-40% risk for thunderstorms

25-30: frequent showers, 40-60% risk for thunderstorms.

30-35: 60-80% risk for thunderstorms.

>35 : >80% risk for thunderstorms.

Red lines & values = wet bulb potential temperature in deg C at 850 hPa.

Black lines & values = height of 850 hPa in geopotential decameter (gpdam).

Critical values for wet bulb potential temperatures.

> +16°C: strong chance for thunderstorms in spring or summer period

http://en.wikipedia.org/wiki/Precipitation_types#Convection

http://en.wikipedia.org/wiki/Equilibrium_level

http://en.wikipedia.org/wiki/Level_of_free_convection

http://en.wikipedia.org/wiki/Convective_available_potential_energy

http://en.wikipedia.org/wiki/Lapse_rate

http://www.spc.noaa.gov/sfctest/help/help_stor.html

http://www.stormtrack.org/forum/archive/index.php/t-4605.html

Shear is a difference in wind with height (or on the horizontal, but we're talking about vertical shear here), so you need to define "shear" over some sort of distance. For supercells, many tend to use 0-6km / deep-layer / bulk shear in combination with CAPE (instability) to determine supercell potential.

Hope this helps a bit!

[BrickFielder]

OK first of all lets have a look at the models, which I think are doing a better job than yesterday, although there is one caveat. I am not sure they have the cloud cover quite right.

I am expecting some clearer skys across parts of the south later on, particularly the south west and possibly the south east coast.This I think puts the models slightly off during the afternoon for some southern areas.

Looking at upper wind levels we have a small jet streak approaching from the south west during the day, with divergence at the left exit and to some extent along the right flank.

Humidity through mid to upper levels moves north during the day, but notice the drier air at 500hpa coming in over east anglia and through the south west at 700hpa. This suggests there might be some good isolation coming up from the south west late on and the possibility of better storm organisation for east anglia.

Vorticity charts would suggest a band of rain moving up through the midlands and another moving up through the south west through wales.

Looking at lightning wizards charts for today you might be a bit worried about tornados and super cells.

Quite correctly this model is picking up a truning of the winds up through the atmosphere, but rather than being concentrated through the mid levels the turning of the wind is mostly at the upper level. Rather than a rotating cloud you might get a anvil streaking out from the storm, rather like the storms over spain yesterday.

That does not mean there will be no super cells in fact the forcast skewT for York looks promising.Notice the turning of the wind in the top right of the chart.

Ok lets look at another skewT this time for the east anglian coast.

What I could draw your attention to is the low level winds, where you have some turning and more importantly a significant difference in the wind speed at the surface and the cloud base. With the right conditions, namely a good updraft then this wind field could produce a short lived tornado. Short lived because without the turning cloud (super cell) it would not be sustained. So we should be asking ourselves what is the potential for a good strong updraft, apart from instability (Cape) and here lightning wizard charts help.

Notice how the cloud base is likely to be higher the further east you are, which is not so good for tornado genesis, but there is some lift suggested across the midlands and east anglia.

Ok one more chart and this one represents low level moisture and I want you to look at the low level moisture coming in from the south west.

That should push up dew points late afternoon which I think could spark off some isolated storms.

Ok lets have a look at a satellite picture to verify how the models are doing.

Not too bad I think although there is that caveat about cloud cover. The MCS travelling up across into the midlands and moving northwards will I think most likely just produce rain until late afternoon in the north when it might start to break up a bit and re-invigorate. So some potential for northern England. The other MCS is perhaps a little more active in that it is driven more by divergence aloft, again I think this will re-invgorate later, but notice the isolated storm tagging along behind. These I think show some potential for the south west and parts of Wales. Notice also the potential for some line convection over France which might come into play if it moves our way. We should also note that line convection and tail storms have a way of creating their own little environments especially with respect to outflow boundaries and storm splitting which can change the wind field. This could pose an isolated severe storm threat.

I feel fairly confident about the scenario for Wales and northern England but less so for southern England where much depends on cloud cover and how things develop during the day. Key places to watch would be southern Wales and northern england (Manchester/ Leeds corridor) with anything else a bit of wild card. There again I could be wrong as there are usually some dynamics I fail to pick up which alters things. I hope it was an interesting insight anyway.

Edited May 7, 2011 by BrickFielder

[johnholmes]

for a VERY simplified idea of where the storms may arrive from and what is needed T and Td to set them off, see the link below

http://forum.netweather.tv/topic/69453-todays-weather-and-general-chat/

look down the rhs for the wind speeds and direction at the various heights, also down that side all the good things you all like to quote CAPE CAP LI etc etc

[knocker]

The main instability in northern France at the moment is around the Brest Peninsula which is not that surprising. The air is quite dry further east. (see Trappes sounding). The brest ascent in quite a contrast. The convective activity is popping across the channel around Dorset and Hampshire. The front appears stationary to the south west and any pricip. is confined to south west Ireland.

Edited May 7, 2011 by weather ship

[staplehurst]

According to both the UKASF Website and their Facebook group, a combination of staff shortages (I guess because it's a voluntary organisation) and site development has lead to a significant lack of forecasts so far this year. Apparently they hope to be back to normal by the end of the month once a new system 'has been implemented'. Sounds intriguing!

[Coast]

Well after a generally disappointing no-show yesterday, ESTOFEX still have a map forecasting some of the UK for attention:

Storm Forecast

Valid: Sun 08 May 2011 06:00 to Mon 09 May 2011 06:00 UTC

Issued: Sun 08 May 2011 04:54

Forecaster: SCHLENCZEK

A level 1 was issued for NE Algeria and N Tunisia mainly for large hail and severe wind gusts.

SYNOPSIS

There are two upper level features on the map which will likely be associated with deep convection on Sunday: A strong upper low west of Ireland moves slowly eastwards and the jet stream on the southern / eastern edge points towards England and Scotland. Some deep convection is expected near the cold front and in the vicinity of the upper cold core.

The second feature is a tiny upper low over the Balearic Islands with its upper level jet affecting N Algeria and Tunisia. Instability is quite low but a good overlap with strong deep layer shear is very likely.

Some diurnally driven convection may develop over the rest of western / central / eastern Europe, but severe weather is not expected. Another large upper low over eastern Europe does not seem to contribute much to the convection.

DISCUSSION

...British Isles...

An upper level vort-max is forecast to move across the British Isles from SSW to NNE during the late morning / early afternoon. In its vicinity, some few hundred J/kg CAPE should be available. 0-6 km shear is in order of 30 - 35 m/s, around 15 m/s shear in the lowest 3 km, but no significant LL shear and 0-3 km SRH are forecast. As mixed layer LCL heights tend to increase around the afternoon, there will be a threat of isolated severe wind gusts. Compared to the day before, severe weather seems to be much less likely and no threat level is issued despite the chance of isolated severe wind gusts and / or an isolated tornado.

Sky Warn haven't yet updated yesterdays forecast neither have TORRO with their update last night just ending.

After yesterday I'm remaining cautious, but if I had to go for somewhere I'd say North Wales into Merseyside with convective gusts, maybe a wee risk of an isolated tornado around 18.00 hrs?

[Adi F]

Well it looks like thats it for the time being on the south coast for a while.

This time last week I started to watch the risk of thunderstorms and possible tornadoes for Monday and Tuesday for Ireland and the North west of England well a week on the trend of each run has continued and the area is roughly the same although it has changed slightly to Sunday and Monday which I mentioned earlier in the week.

I think the area of greatest risk of Tornado activity is for the north west of England and north Wales on Monday between 10am and 1pm. And slightly later in the day, between 1pm and 4pm for the Sutherland area of Scotland. With risk of sometimes heavy thundery rain, possible deep standing water, gusting winds and hail for the South west England, Wales, Northern England, Wales, Scotland and the Ireland throughout the day.

There is a caveat though. There is little correlation between GFS and NMM so I think although there is a risk it remains low.

Edited May 8, 2011 by Adi F

[knocker]

Generally under the influence of the unstable (see Camborne and Valentia ascents) rPM air from the depression to the west of Ireland. Given some surface heating and orographic shove and the 700mb wind flow IMHO the convective activity will more than likely br greatest in N. Wales , north west England and N. Ireland with the distinct chance of a few thunderstorms.

Edited May 9, 2011 by weather ship

[Coast]

Nothing from ESTOFEX, SkyWarn have no alert but say: "Scattered showers, possibly thundery, in a sunny sky but with a fresh breeze. Warmer away from the west."Also nothing from TORO or UKASF so straight into the charts:

If anything the area I highlighted yesterday is still there for me, with it maybe getting East from Northern Ireland across more of Northern England later.

[Coast]

Updated forecast now issued by ESTOFEX:

Storm Forecast

Valid: Mon 09 May 2011 06:00 to Tue 10 May 2011 06:00 UTC

Issued: Mon 09 May 2011 08:12

Forecaster: DAHL

A level 1 threat has been issued across a narrow strip from N

France into the Benelux countries mainly for marginally severe

hail/wind as well as for excessive convective rainfall.

... SYNOPSIS ...

Omega-type upper pattern exists over Europe with a deep

eastern-Atlantic trough over the British Isles that will make

slow eastward progress. East of this feature, an upper

ridge stretches across the central portions of Europe into

Scandinavia. An upper low is present over the Balkans/SE

Europe, which will drop southwestward into the Tyrrhenian/

Ionian regions.

... DISCUSSION ...

... France into Benelux ...

Scattered mainly diurnally-driven storms should develop from

the Iberian Peninsula across France into the Benelux countries.

There will be some 15 20 m/s DLS in the very northwestern

part of the area where storms are expected, suggesting that an

isolated severe hail/wind event cannot be excluded. Especially

over the Benelux, local excessive rainfall cannot be ruled out.

GFS suggests that the best chances for severe weather will

exist over extreme NW Netherlands into the NW portions of

central France.

... British Isles ...

Diurnally-enhanced cellular polar-air convection should develop over the British Isles. It looks like LLS will increase in the early evening hours ... and although DLS should remain quite weak, a brief funnel or two cannot be discounted. However the loss of daytime heating should limit the duration of the severe threat. A LVL1 does not seem to be warranted.

[BrickFielder]

Saturdays forecast did not work out as expected ,what with the milky cloud cover at high levels in places blocking out surface heating. Thats the trouble with storm forecasting there is always that little dynamic that you miss that changes the outcome. Still on to todays potential and in a way I am a little more hopefull today, with some caveats again.

First up an upper level jet streak places anywhere in a line from roughly southampton through to east anglia northwards under the left exit of a jet streak.

Now I would like to compare three forecast SkewT's.London, Birmingham and Manchester during the afternoon.

Firstly we have London where lapse rates are not steep enough, the air is less moist and we have no instability (no storms).

Next up is Birmingham where lapse rates are steeper, the air moister all the way up and we have instability, but notice that cloud tops will top out at around 400hpa.

Next up is Manchester where things are more unstable, the air is moister still and cloud tops are even higher.

From a storm point of view, I slightly prefer Birmingham to Manchester as the moisture all the way up in Manchester could make things slightly messy.

So on to a real measured skewT from Larkhill.

Ok so some of you will be looking at the wind field at around the surface level and thinking tornado potential, but this would have been early morning and may not really be representative of conditions during the day. Apart from that it looks like with some daytime heating it could produce a storm.

What we ideally need for storms is some sort of trigger.A surface trough or mid to upper level trough will do.

Well there is a hint of something at 700hpa for Wales and some noticeable vorticity at 500hpa although I am not sure it over lays instability.

So what about instability today.

Ok neither of those is brilliant and where we have some instability it does not coincide with high cloud tops.

So what about super cells and tornadoes as lightning wizard charts might be possible. Here I am going to point out that wind direction is unidirectional through the atmosphere. Unlike Saturday though I rather like the conditions for a rotating cell today. Here the differential in wind speeds might be enough to think about left moving super cells and storm splitting.

As always it is important to look out the window and see what the actual weather is telling you. What I am seeing is a brisk breeze at the surface which tends not to be good for tornado formations. The clouds are moving along at a fair pace which suggest some wind shear. Cloud bases are mixed with some quite low which would be good for tornado formation.

The sky is quite messy and temperatures at the moment are not that high. On the satellite I am watching the pulse storm which crossed cornwall and how the anvil streaks out ahead, probably somewhat blocking the heating out ahead of it.The track of the anvil is not quite the same as the storm track which is why I say somewhat and this might be indicative of some shear at upper levels.

On balance I am not sure. If it was July I would be tempted to say we will get some storms. The limited cloud top in places, lack of instability push me towards fast moving heavy showers. The pulse storm which developed towards cornwall says otherwise and the fact that it looked circular was interesting. Key places for me might be Ireland, Wales and a hunch says a track from the south west through the midlands to lincolnshire and east anglia, but then I would considering where I live. As ever you know I will have missed a dynamic and the one chart which concerns me is the following one with limited cloud tops. Isolated risk of storms and low risk of an isolated tornado.

Maybe the thing to watch today is the potential for hail with the zero degree isotherm quite low.Back to satellite and radar watching from here.

[Lauren]

Coast, on average how accurate would you say your ESTOFEX map is?

[Backtrack]

Coast, on average how accurate would you say your ESTOFEX map is?

I'm not Coast, but I can tell you that the ESTOFEX maps are usually very reliable, many people on the forum use it.

[Coast]

Coast, on average how accurate would you say your ESTOFEX map is?

They aren't bad, but should never be taken in isolation. They are more of a good indicator - use them alongside some of the other maps and forecasts (such as our own NW one) and see how the details compare.

ESTOFEX has a verification section on their website (http://www.estofex.org/) which explains how they perform and how they asses the performance.

[Lauren]

They aren't bad, but should never be taken in isolation. They are more of a good indicator - use them alongside some of the other maps and forecasts (such as our own NW one) and see how the details compare.

ESTOFEX has a verification section on their website (http://www.estofex.org/) which explains how they perform and how they asses the performance.

I'm too cheap to pay for the NW ones

[Coast]

Nothing from ESTOFEX or Sky Warn for us so here is a handful of charts and indications:

That patch over East Anglia later looks interesting but noting to get over excited about yet......