Ben Sainsbury

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!

Absolute stormgasm charts on the GFS 12z! These are the charts I live for aha, could be some very active buggers should any form!

Don't mind If I do. Under high pressure tho

To me what seems each time is that the excess cloud cover have proved to have not broken quick enough/moved away quick enough. Seems to be a recurring theme to me. CAPE amounts have never looked particularly decent at any point over the last fortnight. It's been a shame because whilst we've had a lack of CAPE, there have been impressive levels of DLS and SRH which if there was any CAPE to tap into, there would be some impressive storms. Hopefully next week we can develop good amounts of CAPE from strong diurnal heating and higher dewpoints etc and should see more lightning activity.

Indeed, Sat24 showing some breaks in the cold coming from the SE. Should expect main bulk of the showers to form in the next hour before intensifying and moving westwards.

Agreed and to admit whilst the uncertainty remains for tonight into tomorrow morning, I haven't been this excited in a long time... Whilst CAPE levels aren't particularly big by any means, we are looking at some significant values of DLS across CS England earlier tomorrow morning and SRH values of 300 to maybe 500 moreso across the East Midlands. When we see low CAPE values and high DLS and SRH values, I wouldn't be surprised if we didn't see any significant lightning activity however I do expect some very well structured and organised thunderstorms albeit very very isolated. In any organised storms, there is a chance for multicelluar and supercelluar characteristics given the large vertical shear values in excess of 40knts. These may bring some nice photogenic skies as we move towards rush hour tomorrow morning, however these may bring a risk of some very severe wind gusts, medium sized hail and a few funnel clouds and possibly a tornado. I personally think ESTOFEX are underplaying the risk for much of Southern UK, however these may be analysed within the next ESTOFEX forecast. Whilst there are large amounts of uncertain and possible isolated nature of storms, I can understand why the likes of ConvectiveWeather are reluctant to issue anything of a higher risk. EDIT: Still an amateur opinion, so please correct me if you want to do so!

Been watching the radar for areas around Exeter, today they have experienced 7 hours of moderate to heavy snow equivalent to minimum dark blue/green echoes on the radar. Must be some exceptional accumulations down there.

Here in Keynsham, we've been stuck on the edge of the heavier snow all day, a covering of dandruff here whereas areas slightly south and west have been blanketed, not again.

Nothing literally, the ground has a white shade as such but nothing of note.

Netweather NMM model currently has a really good grasp on current positioning and intensity of the snow over the south. As we head pass midnight we should already see marked increases in intensity and more so into the realms of early morning tomorrow. Hopefully it can bring the goodies to Bristol!

Powdery snow here in Bristol now, hopefully we can get a thin layering of powder snow before some much larger flaked wet snow tonight to bring some decent accumulations!

Yes you could say that, the mild days have brought the ground temperatures much above zero, however this snow and cold rain falling onto the ground is likely to decrease the ground temperature and into tonight along with much colder air, ground temps are unlikely to get above 0'c and snow will readily settle overnight.

The Netweather NMM Model seems to agree with this very well. Lapse between Sunday 00:00 - Monday 00:00 Snow.avi

Frome is about to get pelted, could expect 3-4cm an hour from that if it all settled!

Whilst we have the potential for snow on Saturday and Sunday; storm lovers don't write today off! Check this image by the Netweather NMM model, certainly the potential for a few storms today developing around M4 and moving northwards. Current showers should intensify over course of the day.

Large changes in areas of interest overnight... Now appears that cloud cover is going to be much less extensive than yesterday, therefore more diurnal heating and more storms should form over the afternoon. Main area of interest today is in connection with a large convergence zone stretching across the Bristol Channel and along the M4, therefore any thunderstorm activity is likely to develop here and move N/NW'wards. Forecast Map Below:

Disappointing day as a whole, a few potent showers but nothing of a note, showers that did form was in conjunction with peak instability values and diurnal heating. Main reason for today not playing out is as a result of far too much cloud cover, temperatures didn't reach values expected. Tomorrow follows a similar story as today with something a little more potent possible across the far south towards the end of tomorrow. General consensus is that any showers will form in connection with any diurnal heating and a convergence zone which looks to set up across East Midlands so that would be my focus for tomorrow. The odd rumble of thunder possible w/ small hail but overall severity risk is slim similar of which to today. Don't have access to my forecast map right now, but a general isolated risk extending across much of England tomorrow. However a risk of some storms (fairly elevated in nature) making its way across the channel later tomorrow (9pm onwards), though these are likely to die out from cool SST's given low bases.