Ben Sainsbury

The showers formed North of Cardiff are a positive sign for those further NE of North Midlands etc. Further SE however, the main area of showers across South Devon are beginning to peter out. The area of cloud whilst expanding seems to be thinning across these areas at the moment.

We have lift-off, small areas of precipitation have developed over South Wales. (Difficult to tell whether radar glitch or not) Some half decent convection taking place over me here, beginning to build up in height somewhat. Sat24 shows this rapid developments in last 15 minutes.

Well here are the Euro4 for 9pm and midnight. Much of North Wales and West Midlands actually miss out, very different compared to NMM Model. According to Euro4, CS/SE England into East Midlands look a treat.

Whilst I normally have trust in Euro4, I'm rather skeptical for what it producing during the day now. At 9am, they have shown no storms to have initiated at all! And they don't even show any storms to initiate until 3pm across SW/CS England, risk looks a little eastwards compared to various other models.

To simplify some of the forecasts I've seen, I've identified the main periods of what storms to expect across the UK tomorrow. We are looking at 3 periods of storms. Ignore the key in the bottom-left I use these for my own storm forecasts.

I completely understand apologies if I was also harsh! It's difficult to explain, when the conditions are marginal a forecast will always be issued than not. Therefore times like this more times than not the forecast will be wrong, so I agree with you there. Anyhow I like that a lot of forecasts have been produced by a large variety of forecasters this time, provides me with greater confidence. And as a matter of fact to me it seems like an eternity since Nick have issued a "Yellow Thunderstorm Area" so I'm hopeful!

You aren't wrong, but I think it's a little harsh what you're saying. In each and every forecast they produce they outline the risk is very marginal and there's as much as a chance that nothing materialises. So whilst their forecasts have been so called "iffy" lately, surely their recent forecast outlines their confidence for issuing such a high risk level.

I always thought a thunderstorm of a large intensity, could effectively “use up” the atmospheric CAPE?

Unfortunately the other parameters aren't quite there for supercell development. But nevertheless with such large CAPE values (for this time of the year anyway) there will be some prolific lightning.

Quite astonishing and something I rarely see on hi-res models. The Netweather NMM model 12z, caught my eye as a small area of Wales witness significantly lower temperatures than the near surrounding area of which this area moves north over time. Check this chart out for tomorrow at 3pm. This really could only mean one thing... SOMETHING must be causing this; some extremely heavy precipitation. After looking at the following CAPE chart, it was obvious a large area of violent thunderstorms must have formed. If this is to happen, then I would expect some extremely violent and well structured multi-cell/squall like feature to form and move northeastwards tomorrow. Interesting times!

Very dull start, looks like the mist is taking much longer to clear, a little concerned as looks like winds coming off the Bristol Channel towards the Bristol Area.

There is nothing better to me as an "amateur meteorologist" receiving these types of comments. Being 18 and looking to study meteorology these comments are what motivate me to learn more, thank you and hopefully we'll have many more of these events over the coming months.

Sounds reasonable, I've never truly understood how Skew-T data was collected and its accuracy which is why I've never really used it. Looks good though!

Maybe I should've been more clear, the CAPE chart I posted was from the Netweather NMM model, maybe it's time I use the same caution with that model as with the GFS. Are skew-t's really much more accurate over forecast models and if so how do we know? EDIT: Ironically this is the GFS 12z run... Which is the same as the skew-t.

Looks like that's the case, I can't see many showers forming before late afternoon. The fax charts show the trough moving west to east at the spine of the country at midnight into Sunday. Majority of showers should form before that, many being initiated about 6pm ish... Before lasting well into the evening/night. Major risk seems north of M4 anyway according to NMM.

Yet to see any forecasts for any of the storm forecasters at ESTOFEX and ConvectiveWeaher and understandably so. Very limited convection as high pressure strongly in charge we may have to wait until Saturday at the earliest!

I'm going to give my overview of the thunderstorm potential for the next few days up until Sunday. The main thing to note during this period is the dominance of high pressure which significantly reduces the risk of storms, along with lack of moisture and high CAPE values for majority of period. A few definitions for those who are learning I'll quickly go through them. CAPE: Convective Available Potential Energy - Measure of amount of energy for convection, therefore higher CAPE = quicker storm formation and more frequent lightning. DLS: Deep Layer Shear - A measure of wind shear between the mid levels of the atmosphere and surface. High DLS values means storms will become more organised and persistent bringing a greater chance of severe characteristics. SRH: Storm Relative Helicity - Measure of potential for cyclonic updraft rotation. Therefore higher SRH, greater potential of supercelluar characteristics. PW: Precipitable Water - Indicates the amount of moisture within the air. Higher PW greater chance of storm formation but too high and atmosphere becomes saturated. Tomorrow (Thursday): As you see from the graphs below, we are seeing SB CAPE values of 1000J/kg, this is as a result of strong diurnal heating. As a result we see a few storms form across CS England into East Midlands. The Netweather NMM model shows the formation of a convergence zone which set off these storms. It must be noted that whilst the NMM model produces storms, the lack of available moisture (precipitable water) and under the influence of high pressure, I cannot see much potential tomorrow. However if a storm does form, the low PW values along with 30-40knts of DLS, means that any storm may last a long time from its sustained updraft. Lighting amounts will be fairly infrequent. Friday: Friday warrants a similar risk to Thursday. CAPE values are fairly higher stretching towards 1500J/kg, but must be noted this isn't important if there isn't any available moisture. Again the NMM model are very generous with the breakout of storms, however precipitable water values are a little higher so I'd favour Friday over Tomorrow. We also see values of 30-40knts of DLS therefore any storm that does form will see more frequent lightning activity as the updraft will be long-lived. I must stress that even with these favourable parameters given high pressure is in control, we are more likely to see nothing rather than something. My best bet is just north of M4/Bristol Channel across SW Midlands. Saturday: A much greater risk lies on Saturday, at this point high pressure tends to move back away to the east. As you see CAPE values are even higher approaching 1800J/kg, showing the potential for some very frequent lightning. The reason there is a much greater risk of Saturday is because of the much higher precipitable water values, lower pressure (whilst still high) and a well-defined convergence zone. DLS amounts are rather slim for Saturday however, storm relative helicity values which represent the potential for cyclonic motion within an updraft, are pushing towards 150-200m^2s^-2. Therefore any storms on Saturday I expect to form along a line from North Wales towards East Anglia and the London Area, a few storms just North of M4, but lower risk. These storms will exhibit the potential for supercelluar characteristics but these will be relatively short given lack of DLS and may only occur within a tight time frame. All storms will have a relatively short duration but will result in some very frequent lightning. Sunday's potential remains to be seen as charts don't quite reach that time frame but interesting times nevertheless. I hope this have given you an insight on what we could expect this upcoming week. I'm still learning myself all the time so apologies for any errors.

Sat24 showing cloud exists all areas of the SW, within the next hour or so.

Agreed if we look at comparisons for 7pm, between the Netweather NMM model and Sat Charts. The cloud is actually moving through very slightly little quicker than forecasted.

Very dull day today here, very hopeful about the upcoming few days. I know others might disagree but from personal experience GFS and BBC in general under-cook temperatures by a degree or 2. I think we could see 23'c - 24'c at some point over the coming few days.

I get you now! That's normally the issue in these setups we can have large CAPE values showing, but being under the influence of high pressure and lack of moisture can be an issue. I would agree that isolated thunderstorms have the possibility of forming, using Friday for example. We have sufficient diurnal heating, a few convergence zones developing and the introduction of a cold front from the NW, I think we may see storms form from West Midlands and later in the day transfer SE. Must take caution but details at this stage are uncertain but using merely as an example. Certainly as you say as pressure begins to decrease late weekend, early next week we could see something a little more widespread. EDIT: Oh and I forgot, though not model discussion, Skew-T's will give us a better idea closer to the time.

I see this being said a lot and you're not wrong. But is the NMM model known for overdoing CAPE values too? Because from what I see the NMM is showing the same if not greater values than GFS. And what do you mean about the atmosphere looking too stable? I don't see any problems.

I’d kind of have to disagree with you, there definitely was some modest instability, steep (ish) lapse rates, wind shear not particularly important in regards the amount of showers that form, moreso the structure and longevity of showers. The main reason for lack of activity was no proper trigger today... The trough really just moved north too slowly, didn’t give enough opportunity for a larger mass of showers to develop, no convergence zone had formed until the evening over Reading etc, hence why the only showers formed across CS England.

Yeah, still a couple hours of sun. The batch of storms in N France formed in connection of a trough moving northwards. This should initiate a few showers across south midlands over the next hour or two (what we're seeing already) though nothing substantial. Still some half decent convection to the NE of here.

Not far off lol See I always thought this was dependent on cloud cover, unless I'm completely wrong. Had a peak at the Netwx Model for same time frame, seems to be half of that of GFS lol. Guess I am wrong all learning!