BrickFielder

Tricky to forecast today in my view. Last nights sounding from Nottingham showed a marked CAP at 700hPa which suggested surface based convection could initiate at around 34C but could become just elevated when temperatures dip below 28C. Yesterday benefited slightly from mid level dynamics which I don't think will be present in the same way today. Much of the modelling shows lower humidity in the south with dew points dipping down to 14C which I have serious doubts about considering the current dew points.Precipitation charts suggest a heat island storm for London with chances of further storms at outflow boundaries (likely to have some low level vorticity). We also have convergence zones with precipitation breaking out where dew points are forecast to the highest (further North). Cumbria up through north west Scotland would seem to have the best chances for storms today, but bearing in mind dew points currently and the forecast dew points I would not rule out storms else where. I am also drawn to the particularly strong outflow winds from a suggested storm over London.

Birmingham inbound storm just skirted Coventry. Looks to be mostly elevated but has some surface based towers towards the back of the storm. Plenty of lightning and rumbling but even the lower towers still have a bit of a high base. Could be good for Photography as it slowly moves north and the light begins to go.

Yesterday evening about 8pm I was watching birds soaring on thermals which is pretty unusual for that time of day. Old folklore suggests that this heralds thunderstorms coming in the next few days. Its clear that there will be some pretty heavy elevated thunderstorms for the south west and up through Wales ongoing through much of the day. There is also a chance of surface based storms which is a bit marginal.Looking at the sounding for Nottingham overnight then it suggests temperatures in the region of 32/33 degrees providing there is a trigger could produce quite nasty surface based storms. The modelling suggest some low level wind convergence as a triggering event possibly around the M4 and Oxford. Looking at the latest wind flows across the UK suggests the forecast for these convergences is not unreasonable. Most models are not that keen on this and forecasts suggest that temperatures may just not quite reach the point of surface based convection.

At the minute I am watching the modelling for late Sunday afternoon. It looks a surface based heat low develops over the South of England late tomorrow afternoon. Forecast SkewT's suggest slow moving very High storms could develop around low level wind convergence zones. The risk here looks to be intense lightning and localized flooding. The problem is this type of surface low is quite hard for models to get right and it may not happen at all or get delayed.

Modelling seems to have made up its mind that there will be little in the way of Storms for the UK today. Looking at the Brest Sounding from last night it suggested that dew-points of 20C and temperatures of 34C would be required to break the CAP. Dew-points that high are most likely out of question but I have noticed a marked difference in dew-points across the country. Heathrow as dew-points at 10C while Cardinham in the south west as dew-points at 18C. Across northern France a lobe of vorticity as sparked of a Storm which is likely to skirt the south east of the UK. We still have a number of low level wind convergence zones and the lobe of vorticity moving north from France. As late afternoon approaches it will still be touch and go whether the CAP goes. Think it is just a case of waiting and watching now.

It still looks marginal as to whether storms occur tomorrow. Some models show a hint of surface based storms for Midlands through to Cumbria moving eastwards during the late afternoon. Some show elevated storms developing over the south east of England during the afternoon or surface based imports from the continent. Looking at the forecast SkewT's I can see the elevated mixed layer clearly and the suggestion that the CAP goes with temperatures in the low thirties. When I look at the soundings from the continent last night then the CAP goes at higher temperatures. Part of the difference is that over the UK tomorrow low level maritime air begins to undercut the elevated mixed layer and meets the dry continental air along a convergence zone. We should also remember that The UK being closer to the front and jet-stream will tend to alter the propensity for instability. Looking at Satellite imagery we can see the first shoots of storm development over Spain and Southern France today. This can be a good or bad omen because it means the air is unstable with higher temperatures but also leaves the possibility of dying storms from the previous day drifting over the UK blocking sunlight. To my eye there is also a thin band of vorticity just ahead of the front out from the coast of Spain. Weather models always seem to down grade storm potential and move it eastwards the day before as certain real soundings (continental) rather than satellite guessed soundings come into play.As other real air soundings come into play(Ireland) then there is a tendency to slightly upgrade storm potential overnight before storms and to move things slightly westwards. Based on this hunch about how models perform I am leaning towards storms still happening tomorrow.

It is too early to really assess the storm potential for Friday, but I can see some potential for storms. These may be French imports or perhaps a sliver of a chance of surface based storms from the Midlands northwards. There are signs of possible high cloud keeping temperatures down which could negate the potential and the CAP looks pretty strong. Worth keeping an eye on as we lead up to Friday.

Still some timing differences in the models.It is worth remembering that temperatures tomorrow will not be that high so low level lapse rates will be weak, potentially limiting updraft potential. It is starting to look like a combination of upper trough and low level wind convergence being a trigger for convective development. Low level wind convergence is tricky to model so exact placement of convection will be subject to change on the day. I should also point out lightning wizard cloud top height modelling which does not suggest very high cloud tops across the very south of the UK.Lightning wizards dynamic tropopause chart also hints that local convection conditions might lead to some over shooting tops though. It also looks like parts of Scotland may be in with a chance of storms as well. It is still tricky to pin point as this stage where and how strong storms might be.

There are slight modelling timing differences for Saturday which are interesting. We have an upper level trough swinging across the UK with GFS modelling showing it arriving Saturday night while MetOffice fax charts suggest that it cross the the UK during early evening. The track record for GFS this year is to move this type of trough too slowly across the UK and the MetOffice to be more accurate but still a little slow. Equally modelling tends to keep the trough a little south of where it ends up. If things go to form and its risky to second guess how weather models might be wrong then we could see thunderstorms Saturday afternoon which may not be on the modelling radar yet. It is difficult to tell whether the trough will be tilted and we need some sort of modelling agreement to guess at potential but it is worth keeping an eye on.

Upper level cold pool of air is forecast to move quite quickly across England today , probably leaving the east just after mid day. Looks like a small window of storm possibility 10am to 1pm for eastern counties. There is a small risk of storms in a small window of time between 14:00 to 16:00 across the midlands and south east as a narrow band of mild upper air cooling traverses across low level convergence zone convection. Winds look light and instability is meager at the most but because storms will be slow moving there is a risk of localized flooding. Slight risk of very weak spouts and key area to watch is probably from somewhere like Cambridge through to Suffolk.

I don't have a lot of confidence in the modelling today as it looks to me as if the modelling is about 3 to 4 hours to slow in moving things north and east. This moves the storm risk further towards the north east in my view. It does however perhaps bring other factors into play which wont be modeled. Here I am looking towards the south west initially. Last time I questioned the modelling though, the models were correct and I was wrong so take this with a pinch of salt.

I have been watching the models for Friday with interest and struggled to get a handle on whats going on. Models still don't exactly agree and the modelling has moved instability about across the UK over the various runs. I think my difficulty lies in the fact that there might be more than one thunderstorm potential here. Looking at the modelling we have an elevated mixed layer with significant instability above the boundary layer. Looking at some of the forecast SkewT's I can see a CAP on low level convection as a result. Where we have low level wind convergence below this then there is potential for enough moisture pooling to break the CAP.The most likely place for this is probably the north east and shows up as a trough on the UK Met Office Fax Charts.Whether thunder storms are elevated or surfaced based the instability is high enough to produce large hail and lightning. We also have occluded cold fronts which will introduce colder drier air aloft which will pass over the still moist low level boundary air and replace much of the elevated mixed layer.UK Met Office fax charts and other modelling do not exactly agree on where they will be.This change to the environment looks capable of breaking the CAP and initiating surface based convection. Models don't quite agree on whether temperatures and dew points will be high enough or how near to the surface that drier air gets. Potentially you have some directional wind sheer in the boundary layer with speed sheer aloft and moderate instability. This is a scenario which can produce an isolated moderately severe Thunderstorm. Some of the charts I am looking at.

Watching the clouds around the storms yesterday I noticed some low level clouds heading in a different direction to the clouds above. This suggests quite a strong inflow and up draft environment that can moderate low level winds. This is something that can happen when low level winds are light and will not show up well on forecast charts. It does mean that you will have some low level vorticity (wind shear) that is very localized. Today is slightly different to yesterday in that we have upper level divergence from an incoming small jet streak. This high level jet should enhance convective height, but also should provide greater up draft and down draft separation. In simple terms we have slow moving, strong and long lived storms. Forecast low level wind charts show wind convergence zones but also hint at localized wind fields. Forecast SkewT's show moderate instability driven in large part by moist low level air (dew points). They also show light winds except at the highest level which we might get high level cloud from early storms streaming out ahead of early storms dampening down storm development. There is also very little in the way of dry air going up through the atmosphere which means convection could be a bit messy. There is also the suggestion that storms may become detached from the boundary layer as we go into the evening. The wind field is also not conducive to super cells (rotating storms) so a clear tornado threat is off the cards (Any splitting storms can change this though) Possible risks are localized flooding, lightning damage (mainly sheet lightning) , possible weak short lived tornadoes. The conditions are there for some severe storms (more so than yesterday)and localized wind winds always make me nervous.On the other hand there are reasons why convection is messy and temperatures are pegged down to limit storms.

Interesting question. It has been suggested that during warm phases of the AMO that tropical storms are more likely to develop into mature hurricanes.However the correlation between AMO and a particular hurricane season is pretty weak and the frequency of storms is largely unaffected.I think during 1971 to 1994 (25 years of AMO cool phase) there were only 36 major hurricanes compared to 1945 to 1970 when there were about 67. It has been suggested that we might just be entering another AMO cool phase, although any affects will be muted by climate change. When we look at hurricane landfalls then there is a marked increase in the warm phase and a shift to the east coast during the cool phase. Personally I believe the AMO is a reflection of the default position of the Bermuda Azores High Pressure. During a warm phase it is closer to Bermuda and is more south west in the Atlantic pushing tropical storms into the gulf of Mexico. During the warm phase high pressure is more North east towards the Azores resulting in tropical storms curving northwards out to sea. The jury is out on what exactly causes the AMO or even if it really exists. The theory which seems to ring most true with me is that cloud fractions and dust formation across northern Africa changes. This possibly being driven by Indian Ocean changes which link back to North Pacfic ocean changes. There has been modelling which shows that the PDO leads the AMO by 1 year and when the AMO leads the PDO by 11–12 years. This seesaw motion being reflected in the location of deep water formation at polar ice edges. This is all complicated by whether the AMO cycle actual is 25 years the same as the PDO or 60 - 80 years as most literature suggests.Perhaps the cycle is disrupted by volcanic aerosols (major volcano eruptions) as some have suggested or CFC emissions. It could also be linked to the Wolf-Gleissberg cycle Solar cycle with a 5 year lag (This is very contentious but supported by a least one paper -Knudsen, M. F. et al.) There seem to be some indications that the effects of the AMO may not behave quite as previous ones have done with some marked implications for North America and Europe. Warmer seas in the Mediterranean and around the northern coast of Africa affect the eastern extent of the Azores. We might also see a weaker gulf stream with a propensity to turn east out into the Atlantic slightly further south along the American east coast leading to a more marked boundary between warmer and cooler waters. This all complicated by droughts and dust as weather patterns change due to the pattern change, which affects inbound short wave radiation and outbound long wave radiation and possibly global temperatures (Although climate change alters this). There are all sorts of conflicting ideas surrounding the AMO. This means I cannot guarantee any of the information here and perhaps somebody with more knowledge will correct a few misconceptions I have. Hopefully yourself and others will explore further and provide more concrete analysis. I hope this gives a starting point as I don't think there is a clear answer.

Potential convective risk Thursday from the occluded front moving up from the south west. While modelling suggests some potential for convective development we should consider that air aloft looks moist perhaps producing a high thin layer of cloud which could dampen down temperatures.Low level wind convergence looks to be in place triggering development which could perhaps create storms behind the upper level disturbance. Combining this with perhaps a warm air inflow from the south and perhaps we could see stronger development. Looking at the skewT forecast profiles then we can see strong wind speed shear in the lower levels, combined with very weak surface winds and convergence which can help with strong inflows. Upper winds look unidirectional and not increasing with height which might limit updraft longevity. Personally I think surface temperatures are too low for strong convection and squally heavy showers might be the order of the day.

Tomorrow is a bit tricky to forecast due to model variances. What we should expect is elevated showers for the south west and parts of Wales overnight. Then it gets tricky due to a cap ,cloudiness due to elevated convection, low level convergence not lining up with upper level dynamics. Dew points of around 17 or 18 C which matches today's dewpoints in some places could release a significant amount of instability. Think we need to take a closer look in the morning.

Chance of a few thunderstorms today where weak low level convergence takes place. Instability is rather meager and winds look to be straight line but increasing with height. This should give some updraft downdraft separation with upper cloud pushing out ahead of the storm. So storms might be long lived but fairly zipping along. Convergence zone look to feed moisture from the north rather than the south and with relatively low dew points and temperatures we should not expect really strong updrafts. There is however just a hint of winds at the 700hPa to 800hPa level being a little stronger towards the East mid afternoon. Storm risks look fairly low with perhaps the greatest risk from convective gusts. Worth keeping an eye on but unlikely to be a classic storm day.

I am looking closely at tomorrow afternoon mainly for an area from Reading through to east Anglia for thunderstorms. Satellite imagery shows the low that has brought the bad weather over Friday beginning to elongate with a vorticity lobe working its way around it. This lobe should head towards northern France but might encourage some divergence aloft. Current modelling suggests a number of convergence zones setting up across the south of the UK. At the same time the upper jet begins to move of into the continent. Some modelling suggests the remnants of the lower level jet may remain over eastern parts. Instability looks meager but lowering cloud bases combined with some low level sheer could produce some localized enhanced conditions. Limiting conditions are upper cloud and weak temperatures which would limit updrafts. Urban heating might just make the difference. Something to watch out for even the modelling suggests very limited possibilities for thunderstorms.

Picking out a particular area for thunderstorms is quite tricky today as Models vary somewhat. The general trend looks to be Ireland , Wales , Northern England and Scotland are favored for thunderstorms. Instability looks to be fairly low and storms should be moving fairly fast. However looking at Satellite Imagery I can see a slight kink in the vorticity pattern with some potential storm development associated with it. This seems to be suggested in the GFS Lightning wizard troposphere charts, however the timing is likely to be different. This is something which should be watched closely and might suggest parts of England in the south west , through the midlands and possibly East Anglia could see a storm during the afternoon. It is tricky to predict and will probably need now casting.

Today's thunderstorm risks look mainly limited to the North East, North Wales, North West Scotland and Cumbria. Storms that do develop could cause some localized flooding. Tomorrow looks interesting although instability is limited. Looks like there is an upper level trough swinging across from the south west in the afternoon. Wind speed shear looks light but there is some directional wind shear in the lower levels. There also looks to be a hint of a low level jet (700Hpa) across parts of the south. If the warm air feed from the south and surface temperatures had a little more time to build up then this would almost be a classic thunderstorm set up for the UK. With storms moving North east and a warm air feed from the south then despite the lack of instability and lack of wind speed shear some significant convection is possible. The limiting factors will most likely prevent storms reaching severe level, but worth keeping an eye on. Sunday sees another upper level trough although perhaps a little later in the day. There is also a suggestion of cloud cover limiting lower level temperatures in some places. Looks like a repeat of Saturday only a little later and there is more significant moisture pooling at the surface with lightning wizard showing strong surface convergence across the Midlands. Upper level winds look stronger so wind shear is higher along with the risk of mesocyclones.Upper Level divergence will also contribute to convective potential. Too early to put any detail on it but severe storms possibilities are a little higher (Slight). More possibilities for storms Tuesday. Key areas look like being south midlands both Saturday and Sunday although upper level support and convergence/ moisture pooling at the surface may not overlap which would limit convective potential.

The energy which was feeding the storm yesterday has mostly gone and the entrainment of cold air is limited now. What we are left with is a filling low with rather messy rain bands (not discreet bands). If we add into that the details from the overnight Camborne Sounding we can see the propensity for high level cloud. This will limit surface temperatures until the low starts to fill a little more. What the Camborne Sounding does show is that the instability is more than forecast from quite moderate surface temperatures. This is then complicated further by the center of the low not moving north east quite as predicted and only just coming ashore in the last few hours. What we can see is some clearing of the bands to the south of the storm and some weak vorticity bands associated with those bands. Key area from the modelling is North Wales moving into Cumbria but considering the storm track that is likely to shift. So it is another watch and wait and see scenario.

Satellite infra red imagery from the early hours of this morning showed quite a dark core for the low pressure system out in the bay of Biscay. I would take this to show that the low pressure system was deepening quite rapidly at this point. From the imagery we can see a cooler air feed becoming entrained within the system which has been feeding the enhancement. Lightning Wizard charts show a couple of things. Firstly significant propensity for spout development for the south west into the evening and overnight. Secondly a marked upper level trough swinging across the UK ahead of the center of the low.Thirdly quite strong convection gust potential south and east of the low pressure system. Looking at Forecast SkewT's I can see weak instability for the south west late into the afternoon with quite a bit of wind sheer. For tomorrow we see a pretty moist profile all the way up (which suggests messy convection). I am not sure how much I trust these at the moment. Taking all of this into account then the forecast filling of the low and tilting might be a bit delayed. Upper level temperatures associated with the low might be a bit cooler than forecast where cooler air has become entrained.I would not rule out the possibility of a slightly wider area (Southampton through south midlands and into wales) being at risk of thunderstorms late afternoon. Prime risk is going to be for the south west including into the night. Water Spouts and very weak tornadoes should not be ruled out for this area. Tomorrow at the moment looks a bit messy and I would not like to put much detail on it till we see how things develop today.

It is a bit tricky forecasting today. When I look at the GFS based forecast SkewT's I see a number of problems with the forecasts. 22 C top temperature for Cardiff when it is already 26 C. Dew points of 25 C for Cumbria later. So basically I am not taking much notice of these. Then we have the fact that the jet stream around Portugal is further east than forecast which makes it a little hard to predict the angle of the jet stream over Ireland. Looking purely at the Satellite images then I think we have three distinct possibilities for Convective activity. The first is a small trough currently over the South Coast which I think could enhance as it moves northwards (South Midlands and East Midlands) with perhaps some follow on storms . Ahead of the cold front we have clear evidence of a trough which may affect some western areas later. Lastly we have the horseshoe shaped trough over northern France due to heat build up and this is the feature which is likely to move north and give the elevated storms during the evening and overnight over the UK.The exact areas affected will depend on the placement of the jet stream towards Ireland. Now forecasting seems like the best course of action although we can say there will be elevated storms over night giving strong convective gusts and significant electrical activity.

There is a bit of divergence in the models about Thunderstorm potential for Thursday. There is a marked CAP on convection across the UK , but surface heating and moisture pooling could just break that CAP (especially in Northern France) depending on which model you look at.Looking at forecast SkewT's suggest the CAP can go at around 36 C with the result that a lot of instability could be released. Bearing in mind yesterday I might question that temperature and think it is likely to require temperatures closer to 38C. Most of the models break out elevated thunderstorms along a convergence line from Kent through to Manchester during the evening which will move eastwards with the focus more on the northern part of this line. Earlier in the day from about mid day there is another convergence line from Exeter up through the western parts of Wales but models suggest the CAP is too strong at that point in the day (looks a bit touch and go from the forecast SkewT's).If the modelling is correct we should see a repeat of Tuesday night affecting eastern and northern areas with just a chance of something surface based affecting Kent late afternoon. Thunderstorm forecasting is always tricky and convergence zones tend to move about a bit from model run to model run. To assess these parameters I also look for clues in the satellite imagery (Not much clue here).I am also curious why the lightning wizard surface to 500 meters lapse rates across the UK in the afternoon are patchy (Cloud Cover or Heavy showers would do it). Weather over Spain and Portugal early tomorrow should give us more of clue. There are two marked differences from from Tuesday Night which are that the parameters for hail and the parameters for strong convective gusts are higher. This tells me the stronger jet stream over Ireland may play a part even though the divergence aloft is a lot weaker and that storms that do develop will be tilted (long lived) and pretty fast moving.

Reasonably happy with jet stream modelling today and reasonable agreement across the models that there is some thunderstorm potential today. Predicting the destabilization of the CAP time wise is a bit tricky as the vorticity patterns across France and Spain are complex (EUMetsat Real time images). It looks to me like destabilization across France might not happen quite the way it is modeled due to fairly dry air at lower levels (More towards the Brest). Divergence of air aloft as a jet streak approaches the south west of the UK into the evening will most likely break the CAP. Timing wise then I think it is going to be later into the evening which will tend to rule out surface based storms although the night time surface inversion is pretty thin in places.Estofex highlight severe wind gusts, large hail and locally excessive precipitation as the prime concerns, but I think we should add lightning to that list. I think west will probably be best due to more moisture being sucked in from more maritime air.