BrickFielder

Plenty to look forward to tomorrow maybe. Still way too early for any detail but sometimes it is fun to look at possibilities in the models. Overnight We have the potential for a Kent Clipper , which NMM thinks will be a near miss. Plenty of rain there for Wales as well although I cannot see much instabillity (CAPE) at that time. Tomorrow What I am curious about is the twin cold fronts showing on the fax charts for mid day tomorrow. 300hpa humidity charts suggest a marked area of cooler drier air moving up from the south between the fronts. This for me might suggest an area of enhanced convection tomoroow perhaps between 11am and 12am. Most likely directly over Peterborough or maybe it just skirts Peterborough and and makes a direct beeline for Doncaster. Just joking at this range its bound to change. Other things to note are the jet aloft to the east of east anglia and some low level wind which is at a different angle to the prevalent flow. Most of this wind turn is in the lowest level, which suggest some low level vorticity available. Winds aloft are straight line but moderately increasing with height. This should give some updraft downdraft seperation, helped by that little bit of veer in the low level wind. So some possibilites for severe weather but not really supercell characteristics (a little speed shear from one side of a storm to another is about it). If the cloud cover was a litle more broken and temperatures somewhat higher You might fancy local conditions to develop an isolated severe storm. Some post frontal instability remains and with perhaps a convergence zone over the south west we could see some isolated storms in the south later in tha afternoon whilst thundery weather from the front continues to trundle north. Still way to early for any of this kind of detail, but sometimes it is fun to see how models develop and change. Just take it all with a pinch of salt at this point. (Definately Doncaster) (Tongue in cheek of course)

Some slight differences across the models. One I would like to pick up on relates to the suffolk and essex area late afternoon (1600 to 1800). NMM is suggesting a low level convergence zone here. 500hpa humidity charts suggest a potential cap breaking here as moisture gets pooled. Other models dont seem so keen on it. Forecast SkewT suggests turning winds in the lowest level and it just about taps into the jet above. Maybe cloud tops will not be high enough here with cooler drier air not quite arriving on time. Second one I would like to pick up on relates to the Liverpool and Manchester area again during the late afternoon.There is marginally greater deep layer shear here as well. SkewT suggests tops upto 350hpa with the cooler drier air aloft. Two important charts for me are the following today. 700Hpa vertical velodity charts are not that impressive. Looking at Satelite pictures there might be some cloud ahead of the front and timing looks a touch late to match the models. Some evidence of a line of convection out to the west of Wales. Key area Likely to be south wales and am not convinced about development for the midlands. Tricky to call. Think cells developing over south wales will travel into the midlands on the back of 500hpa winds. Think you are better off looking at the radar than models for today.

A lot of factors come into play today and it is not easy to pinpoint all areas with storm potential today. Two areas stand out as obvious candidates for storms. The first is along the east Anglian coast and the second is Lincolnshire up through east Yorkshire where low level winds converge. Winds aloft can often play a part in enhancing convection. Generally speaking longer lived storms tend to have stronger winds aloft as the up draft and down draft areas become separated. Stronger winds aloft especially if they turn with height will provide an environment for super cells or rotating cells to develop. There is however another factor which comes into play and that is divergence in the winds aloft which will tend to enhance the generally uplift of the air column. Humidity charts can often give clues as to where troughs and fronts are. If temperature drops then humidity rises, so a line of warmer air might indicate cooler air. Typically this will also show up on vorticity charts and ahead of that area would be an area of positive vorticity advection. This may come into play today. This affects south wales from about mid day through to late afternoon and then central parts of the UK later. Wind shear is pretty low although there is an area in east Anglia where there might be a little, so this might be a key area to watch. There is still reasonable instability which tends to peak late afternoon. So having made a chart posting extravaganza, the details of where exactly storms will initiate is still a mish mash of ideas. Key areas to watch I think are south wales early to mid afternoon. East Anglia although models are not in agreement as to where exactly. Perhaps the north east and parts of the midlands and towards London from mid afternoon and east kent late afternoon. I think because of the weak wind shear storms are likely to be pulse storms with perhaps the exception of east Anglia. There will be some risk of weak spout type tornadoes in eastern areas, along coasts and south wales. With light winds daytime temperatures could reach higher than predicted which can provide a good inflow to storms that develop. Its the type of environment where an isolated storm can produce its own wind fields. Over all the forcing mechanisms seem a little weak so storms are not guaranteed and because of the upper level wind fields particularly severe storms seem unlikely. It is of course a complicated set up so things can change. I hope you enjoyed this little tour of charts even if like me you still cannot nail down the potential today.

Can someone here give me a technical explanation on what happened to the "Mothership" storm last night? Storms require heat and moisture to keep them going. When the storm moved out over the sea one ingredient was removed, namely high temperatures. Because the storm moved across overnight, temperatures were beginning to dip and may not have been high enough to get deep convection initiated to reinvigorate the storm. In this particular case I think there was an additional parameter in that upper level winds and temperatures were not quite as conducive for storms over the UK as over France earlier.

Storm moving through Coventry now. Leading edge of the storm saw low level cloud fairly zipping along. Once it started to rain we have had a proper deluge with fairly frequent lightning. There is a fair amount of static in the air making your hair stand up on end. Not much in the way of hail but a few dots of hail mixed in with the rain. Key risks were very heavy rainfall, blotting out almost all cloud structure and the constant reverberation from the thunder. No evidence of rotation and post storm low cloud is not zipping along like pre storm clouds were. Few towers behind the storm which might suggest back building. Definitely not one of those rather weak storms with a few flashes of lightning.

Tricky to forecast today, not least because there is a lot of cloud around to subdue convection and I don't see it clearing much. So this will not really be any sort of forecast but more a discussion about ideas. The current satellite picture is interesting. Firstly I noticed an overshooting top in the MCS over the north sea. It kind of reminds me of an MCS which crossed Mallorca I think back 2007 which produced a weak tornado. Next I notice the orientation of the frontal zone which I think is more slanted than models would suggest, and seems to perhaps have a trough ahead of it. There also appears to be an area where the frontal area is a bit broken over north France. That break in the frontal zone does sort of show up in modelling. For instance as perhaps drier air aloft. It also sort of shows up at lower levels creating a sort of weak surface low and a bit of a low level jet under it. Then perhaps it is me just paying too much attention to the models and reading things that are not there. I guess many will be reading this and wondering what I am blathering about and want me to spell out why this stuff interests me. Low level jets mean vorticity which with a strongly unstable environment can be lifted to form a tornado. Drier air aloft enhances convection. So if the cloud does begin to clear and the modelling has some semblance of reality then there might be a short window of opportunity for a severe storm. Judging by the way the models have struggled with this scenario, its more of an interesting discussion point rather than any real potential. Leaving that aside I was also interested in the following lightning wizard chart. This would suggest to me that there might be potential for some sizable hail. NMM suggests precipitation will likely be as follows during the afternoon. Broadly speaking I think is suggesting convection in the right areas, although I can already see some divergence between the modelling and reality already, so a large pinch of salt is required for anything discussed or shown above. There is a very real risk that nobody will see a storm across the UK today, although I am kind of thinking otherwise. We might have to wait until late afternoon (which might favour the north midlands northwards) and you cannot rule out the shear raw potential towards east Anglia. I am still kind of wondering what to make of that potential low level jet though and whether it coincides with other factors. Perhaps somebody else might like to pick up and discuss some of these features.

Overnight Still a complex setup but it looks like from about late evening a severe storm in terms of lightning crosses into kent and moves up through into east anglia. A little later from about 2am onwards another pulse of storms move up across the isle of wight into the midlands. Since these form in a spanish plume environment and are crossing the UK overnight then there is a good chance that they will not be surface based. (sometimes storms can modify their environment to be surface based) The high cloud tops associated with these storms would be condusive to lightning. So dont be surprised if you get an early wake up call. Tomorrow I am not to keen on putting much detail on tomorrow at this point. There are perhaps a few charts though that should be pondered on. The highest instability (Cape ) is not necessarily where storms will develop. You need to take into account convection inhibition (CIN) and where the forcing mechanisms are (vorticity - surface winds). Mid level lapse rates tend to decline over the UK tomorrow which limit storm severity. The frontal boundary becomes more marked as the day goes on tomorrow and a lower tropopause means lower cloud tops. It is still too early to tell about tomorrow, but it looks like a Cap (just over 900hpa) goes during the afternoon and when combined with some low level convergence and a low level jet (925hpa wind) then there is a window for some severe storms to develop despite some of the factors mentioned above.

Marginal chance of thunderstorms today with weak mid level lapse rates, which means cloud tops are likely to be limited.Forecast Skewt's suggest up until mid afternoon for most areas a Cap exists at 500hPa. In addition lightning wizard level of free convection charts suggest limited lift apart from some southern counties late afternoon. Wind convergence aloft for the most part will not help either. Showers/Storms seem likely to initiate along low level wind convergence boudaries where moisture pools possibly aided by orographic lifting and definately in response to diurnal heating. NMM charts suggest some vorticity approaches from the south west during the day and another sliver moving up through the eastern central part of the UK from the south. There is some wind speed shear through mid levels and some marked directional shear in the 925hpa to 850hpa region particularly towards the west. Some possibility of very weak convergence type tornadoes and updraft downdraft seperation due to shear aloft, but directional shear seems at the wrong level for super cell development. There is a sliver of drier air at 500hpa which could enhance convection from the isle of wight to lincolnshire. Key area to watch in my view would be somewhere from around Glastonbury through to Reading and perhaps as far as London particularly places just north of London.

Interesting divergence of the air aloft during this afternoon which may help convection. At lower levels some convergence which should provide a little low level vorticity and I have picked out a few areas that I think are interesting. In terms of where the occluded front is late afternoon and some potential troughing then I have highlighted some areas likely to see some positive vorticity advection. In terms of where the best instability is then I think we have some moisture pooling (higher dewpoints) towards east Anglia which could iniate strong storms. It does look as though surface based instability might be a little limited under the occluded front in places. This would mean updrafts would be weaker here and unable to lift and low level vorticity. I do want to highlight one particular area where perhaps there might be a smidgeon of a low level jet. This would increase the difference in wind speed between the surface and cloud bases providing another (low level convergence ) source of low level vorticity. Nmm suggests some pretty potent rainfall in places. Stronger winds aloft to the south and perhaps a little turning of the winds especially in the east could just about produce a super cell. My gut feeling is that we should watch an area from perhaps somewhere near Northampton through to suffolk and Norfolk from mid afternoon onwards for more severe storms. Earlier in the afternoon keep an eye on parts of Wales.

Early on today most of the Uk is under High Pressure and this will prevent any convective development. Its not really till late afternoon and then into the eveing that widespread lift is available. A small low pressure is expected to build just to the west of Ireland. Satelite seems to confirm this. This should increase mid level lapse rates across the UK as it develops. Mid to late afternoon on shore wind breezes set up a convergence zone across eastern England and perhaps wales. This looks like the trigger for convection as moisture is pooled along this convergence area. As the afternoon progresses it looks like the weak low towards Ireland begins to collapse just leaving a trough reminant which should cross the UK into the night. This may pop up a few showers late into the evening, but they are at best weakly surface based. I am not quite sure about this in terms of storm potential. Key risk I think for me is localized flooding as storms are likely to be slow moving and keep building into the evening. Slight risk of a convergence zone very weak funnel, but upper and mid level winds look weak so supercell development looks unlikely (Perhaps a very slight chance south wales). Some wind divergence aloft (300hpa) should help tops to overshoot slightly during the late afternoon. Key areas I think are the wash area, lincolnshire, humberside and north east yorkshire late afternoon.

Last chance of storms for the UK today. The very high levels of moisture have exited the UK. The high tropopause which allows storms to build to very high levels has come down as the low pressure to our west moves in. On the other hand we have some quite steep mid level lapse rates moving into the UK and a some surface based instability. Forecast SkewT's show a bit of a cap at 800hpa which relaxes as the day goes on. 500hpa charts show some vorticity advection moving across the UK. NMM suggest that the cooler air aloft might be behind that vorticity advection. We should however note the presence of a low level jet (925hpa winds stronger than 850hpa winds) Any strong updraft could lift that low level vorticity. There is also some very dry air coming in aloft which would help to enhance any convection. Over all there is a risk of some heavy showers with low tops reducing the risk of lightning. The low level vorticity suggests a risk of weak tornado development. Upper level wind shear will be leaving the UK, but there might be enough for an isolated mesocylone towards the south and east of the shower boundary. Although the Birmingham tornado developed out of environment with low tops and a low level jet the temperatures and dew point that day were a lot higher, so risks are likely to be small. Wales through to East Anglia and northwards most likely to catch a shower.

Difficult to forecast todays potential since there is still some differences in model output. Looking at the Satelite pictures you can see a ribbon of vorticity (red) over the continent with warm air moving up from the south (green). There is also a small area of vorticity moving into the south of the UK which I think might destabilise things from the south west across to the north east this morning. Further south is a vorticity lobe creating a marked cold front and low pressure, which may start to pull that ribbon over the continent more northwards and westward. This afternoon models somewhat disagree about where low level wind convergence will take place. Moisture pooling along the convergence zones could spark some storms. GFS would suggest from London up to Manchester with storms travelling north from this line. NMM has a convergence zone todays the central south of the UK with storms which will travel north into the midlands during the evening. I think NMM is possibkly the odd one out today. Mid level lapse rates are marginal across the UK with cloud tops not being as high as on the continent. Storms across the UK today are likely to be limited in strength. Overnight lightning wizard charts initialized with GFS data suggest the possibility of an import with an over shooting top. This I think will be what the estofex forecaster will be looking at. Not every model agrees and a storm could just clip kent or trundle rigth across the south east. GFS looks keen to bring that ribbon of vorticity ove the continent towards the SE of the UK. With the jet over the UK there is potential for any large storm (limited by lapse rates) to develop super cell characteristics. Low level convergence zones would pose a slight risk of a very weak funnel developing. So there is a slight risk of storms across the UK today with limited potential for a lively import into the evening and overnight.

Cell just passed over Coventry producing thunder and heavy rain is heading towards Leicester.

Well Saturday did not really work out as expected, although some areas did get storms. At the end of the day we can only go by what the models show us, but it became clear looking at satellite pictures Friday evening that things would be a little different to forecast. It seems to me that models have a bit of a problem with a cyclonic vortex which may have multiple smaller cyclonic areas. Here is what GFS made of wind speeds to our west. An Eumetsat satellite picture demonstrates what winds to our west really looked like. Now I know there are no soundings out in the Atlantic and no measuring stations, but it seems to me satellite analysis by the models was poor in my opinion. Bearing this in mind there is a risk of storms today mainly across Ireland and Scotland. However models would suggest that there is an area from north wales through to the north east where some convection could take place. Forecast SkewT's suggest convection is likely to be a little low topped. So some risk of heavy showers for Lincolnshire up to the north west late afternoon, perhaps taking advantage of urban heating at peak daytime heating. Perhaps also a suggestion of development in east Anglia. Looking at Satellite pictures I think I would be tending to look towards the south west and south coast. Looks like a storm has developed over the north west coast of France which is heading towards the UK. Think forecasters are going to be taking a closer look at satellite pictures this afternoon.

06Z NMM Modle output much keener on the overnight elevated storms. Still developing storms from early morning onwards. I should say that there seems to be some agreement in the models about overnight now, but tomorrow daytime still differs from model to model.

My current thinking has changed somewhat from yesterdays thoughts. The divergence aloft no longer appears enough to support an MCS in my view. Atmosphere looks strongly capped at 850hpa, but the cap looks to weaken as the cold front approaches. Which marginally shows up on the 850hpa temperature chart. There is however another posible mechanims for storm initiation on the current model output and thats low level wind convergence, which will tend to pool moisture. The pooling I think shows up on the thetae chart. Low level winds are very difficult for the models to forecast even 24 hours out so expect some changes before the event. I now expect some elevated storms to develop overnight out over the bay of biscay and trundle into the south of the UK in the early hours. Perhaps giving an early wake up call to those in the south. As the day progresses then there is a chance that storms could become suface based (seems likely to me). The Cap is likely to be back in place across the south by the afternoon as far as I can tell. Which could maybe break in the afternoon in the east. Some SkewT's Elevated storms ? Highest convective precipitation. Afternoon storms at peak heating ? Its still too early to tell and higher level cloud cover could keep surface temperatures down. Considering how models have changed over the last day, I would not like to call it at the moment. Very slight super cell and tornadic activity form the midlands northwards possibly concentrated around Lincolnshire and east midlands. Models seem to always down grade convective activity risk at about 24 hours out and then slightly upgrade as the time line shortens. In my view there is now a greater risk of an isolated severe storm than yesterdays modelling would suggest.

Saturday just coming into range for the high resolution models. Looks a bit like an MCS. Surface high isle of wight in response to surface low towards exeter ? Veering winds in the lowest level further north. Possible 850hpa trough, temperature drop , breaking a cap ? Still not enough details. Still a lot can change.

Not sure I would totally agree with the suggestion that the Met Office are useless at forecasting thundery outbreaks. I think there have been significant improvements, but convective forecasting is difficult and they get it wrong sometimes. As do I for that matter and we are totally reliant on model output.

Some early thoughts for Friday into Saturday, although I must stress that its way too early to put any detail on this. The first detail that stands out is divergence aloft moving into the UK and a high level jet approaching from the south. That kind of divergence aloft always makes me think about an MCS. MCS in my mind tends to be lots of cloud and heavy rain with a bit of lightning and thunder thrown in. It has been suggested that this is a typical spanish plume, by that I mean that the source air flow is across Spain where it gets lifted by the iberian plateau to create an elevated mixed layer. Typically from this storms are not surface based but can give a good high level lightning show. I have mixed feelings about whether this is true. Low level flow is a bit mixed. This in contrast to the steering flows at 850hpa and 500hpa which tend to just clip Spain, but it may make a difference in moisture levels in the lowest levels and whether storms are surface based. Now four charts to compare and a challenge for you. So the question is why does the convective precipitation not overlap with the highest lapserates and mixed layer Cape . Why might the deep layer shear be more westerly based. Clues i think are in the air flows at different levels and positioning of the front and vorticity differences. Finally a proper FI (Fantasy Island) chart or just plain scary. Which suggests high cloud tops for the UK (more chance of lightning) , very unstable atmosphere (think strong updrafts and hail) , wind speed shear going up the atmosphere and some directional and speed shear in the lowest level. Not quite a classic super cell , tornado SkewT due to lack of directional shear aloft, but impressive for the UK. It is however at this range almost certainly a misrepresentation of how the air profile will be on Saturday. The typical spanner in the works for this scenario might be storms developing over France overnight and leaving dull, damp conditions under stratiform, cloudy skies during early the next day which takes too long to clear. So it could still be a complete bust,but something tells me that the divergence aloft will have its say. Biggest threat might be localized flooding.

One or two embedded storms in the occluded front over the uk and as it moves north and temperature rises we could see some heavy rainfall totals. The steepest lapse rates don't arrive until the afternoon from the South East though. Charts which caught my eye today. Low level wind convergence in some places, meaning winds will be turning potentially in the lowest level. Some places will have winds gently turning through the mid levels. The winds are light so its not really an indicator but its still interesting. A bit of a dry slot at 700hpa height meaning possibly a bit of cloud clearance. Dry air coming in aloft from the south east. Some divergence at the mid levels helping lift and vorticity moving north. Oh dear. Not much instability and lift. Temperatures and cloud cover maybe scuppering storm potential. Over all its a bit hard to tell although I have noticed a few weak storms over north france so there is some hope. Favoured areas for storms might be South east moving into the Midlands late afternoon. Up draughts are not likely to be that strong and wind sheer is generally low so severe storms are unlikely. Very slight risk of short lived tornado based on observations that low level cloud is not hanging about and there are indications of some wind convergence in places in the models.

Thats a 850hpa wind chart so it will not show surface convergence. I was thinking more about the nose of a low level jet. The surface wind flow chart looks as follows.

Think the low pressure system is a little East and south of where models forecast it to be this morning. It also looks as if there is some mid level dry air in front of a partial warm front stretching down into northern france. Here are a few charts which caught my eye. So a potential warm sector and triple point ? I think cloud cover, poor surface temperatures and weak moisture flow might play a part today. Key areas seem to be South Wales and bristol area and the Leeds to Manchester area. Note that wind shear is better towards the north of England and I think Estofex is maybe looking at low level convergence. Just a hint of a trough in the warm sector could spark some storms this afternoon in southern western areas perhaps up into the midlands. Having said that I am not convinced the models have exactly nailed this and weak instability means storms are unlikely to be widespread.

Estofex mention the nose of a low level jet and low topped supercells which makes me think about the Birmingham Tornado for eastern France. Temperatures that day were a lot higher so I dont think the comparison is apt for today across the UK, but it is is interesting that they mention it might reach the south east in the evening. Looking at the NMM model I can see suggestions of low level wind convergence and this seems to be the area that NMM is keen to develop convective precipitation. Lightning Wizard Charts for the level of free convection suggest convection will only occur across the very south of the UK until late in the afternoon. Looking at Forecast SkewT's I think this represents a CAP between 850hpa to 700hpa heights which will erode from the south. Differences in 700hpa vertical velocity seem to confirm this. Wind shear both in terms of speed and directional shear is poor in the west and slightly better in the east (Suggesting supercells and tornadoes are not on the cards). Any significant pulse storm could have a right leaning inclination by way of differences in the wind shear on the right and left flanks. Which makes me wonder about storm splitting potential, but thats a complicated process and tends to have more to do with internal storm dynamics (Outflow boundarys and the like). Forecast SkewT's for Birmingham mid day suggest some wind shear in the boundary layer, but it tends to disappear later on. Over all I am not convinced by the model output. Timings for different components dont really come together that well except in the south and conditions according to the models should favour the East. Having looked at the Satelite pictures I have come to the conclusion we are better of looking at the Radar and satelite than the models now. Am currently watching the developing storms over north east France.

Some quick thoughts on Cape and Instability. Lets say you have a parcel of air at the surface and it has a temperature of 20 C and a Dewpoint of 14 C. As this air parcel rises it would cool at a rate of roughly 5.5 degrees per 1000 feet, until it cools to the Dewpoint temperature. Once it reached dewpoint temperature then condensation takes place and it will cool at a rate of roughly 3.5F per 1000 feet. If the parcel ascended 1000 feet from the surface and the temperature of the air there was 14 C the parcel of air would be 14.5 C and so warmer than the surrounding air. This parcel of air would now be bouyant and continue to rise. If the parcel ascended another 1000 feet and the temperature of the air there was 10 C the parcel of air would be 11C and so warmer than the surrounding air. This parcel of air would now be bouyant and continue to rise. If the parcel ascended another 1000 feet and the temperature of the air there was 8 C the parcel of air would be 7.5C and so cooler than the surrounding air. This parcel of air would now stop rising. (This would be a CAP on convection ) Convective Available Potential Energy (CAPE). CAPE is directly related to how warm the air parcel is relative to its surroundings.It can indicate a propensity for air to rise, condense out and form cloud. This implies that the steeper the lapse rate ( the rate at which temperature drops with height) the greater the instability. The moister the air (higher dewpoint / humidity) the greater the instability. The colder the temperature aloft (usually associated with low pressure) the greater the risk of storms. Any layer of the atmosphere where temperature rises with height or cools only marginally can be a barrier, stopping air rising (It does depend on moisture content and how far it has already risen i.e. if it is already considerably warmer than the surrounding air when reaching the barrier it may still be warmer at the top of the barrier) There are of course other mechanisms by which air can rise which can help. Air rising over mountains, wind divergence aloft as air rises to fill in the gaps, colder air undercutting warmer air, low level wind convergence (having no where to go but up) etc.

I think its too early to forecast much about tomorrow. This evening we might have a few storms clipping the east coast as a trough in the warm sector clips the coast. Models dont really agree on the positioning, with the NMM suggesting this might be out to sea. So a possibility of an off shore light display, although I am not convinced. Overnight a front moves through giving some moderate rainfall and by ealy morning is across the north midlands and Wales. It looks like the sun breaks through the cloud over very southern areas by mid morning with some cloud bubbling up as a result. The upper level jet is to the east of the country as are the steepest mid level lapse rates and although there are signs of low level wind convergence across east anglia , low level moisture arrives late in the day. Convection does not look like over lapping with any appreciable sheer either except perhaps the very east. Forecast SkewT's suggest a cap at 800hpa which only relaxes later on. Over all shifting things 50 to 100 miles east or west will make a big difference. Speeding up the clearance of the front or changing its orientation slightly will also change the possibilities. So at this point the models can give you a hint of possibilities, but we could also easily end up with no storms tomorrow. So its too early to tell at the moment.