staplehurst

The thing to bear in mind about the warnings is that they aren't specifically for lightning, and cover a very large, broad area - their main interest will be the impacts from heavy rain / flooding. Overall the risk of storms has looked highest over northern England today, for the past few days now. Apps should always be taken with a pinch of salt in showery conditions as they will struggle to predict showers in the right place at the right time. On top of the showers being in the wrong place, they also then have to work out whether such shower might produce lightning or not - so you can see how quickly they can become 'wrong' in a forecast sense. Days like today it's always best to follow the radar, and if you have a specific interest in lightning then follow and read the forecasts from the various convective forecasters out there.

Depends which forecasts you look at

We quite often see posts claiming 'we haven't had a storm here in 5 years', 'the south east always gets the storms' etc - so I thought it would be interesting to see just how many days of thunder we've had across the British Isles so far this year (up to the end of June, but in reality there hasn't been any lightning in July so far anyway). This map contains 6 months worth of lightning data, with slight smoothing applied to make it a little easier to read. The white areas signify where no lightning has been detected so far this year. The most thundery places appear to be the Crystal Palace area and Templeglentan (Co Limerick) - both areas have recorded 6 days of thunder so far (a 'day' is considered the period 06z - 06z)

Primarily because there's a strong cap in place the past few days - so strong (and hot) that we set a new record for the highest 850mb temperature observed in the UK yesterday. Pretty much all of the thunderstorms in the past 7 days have been elevated, as you say, driven more by upper forcing than anything at the surface. These can still deliver large hail though, given the magnitude of CAPE and very steep mid-level lapse rates.

Lack of agreement in the models (and still is!) to feel confident enough to include a SLGT last night...

I know not strictly related to convection per se, but related to those tephigrams and the pronounced low-level temperature inversion (essentially a lot of hot air from the Continent riding over the top of a cool undercut) Because the inversion is so low, there is a 'tight squeeze' of the easterly winds flowing over the moors of SW England - this creates a much more turbulent flow on the lee side (so in this case the west side of the moors), where we've seen gusts of 50-60 mph today. These can be quite localised, and hence have a tendency to blow lorries over suddenly etc

Couple of interesting tephigrams from today, showing a plot of temperature (x axis) with height (y axis). Camborne in Cornwall had 2,000 J/kg CAPE at midnight, reducing to nearer 1,100 J/kg CAPE at midday. All elevated above the elevated mixed layer. Incidentally, some very warm / hot air just 1,000 ft above the ground, creating a strong low-level inversion (and hence strong cap). You would need a surface temperature of 43C to break the cap / warm noses though. and this is what 2,000 J/kg CAPE looks like in an environment with no trigger...

yep, Summer Sun posted it last night a few posts up on this page

So pretty much as forecast for pre-midnight then

Initiation should be around 8-9pm over NW France

Look away now - unless you live in Kent of course... 12z AROME fancies a repeat performance of last Tuesday

Very jealous, it's reached 28C in our office so far with condensation on all cold surfaces (such as water bottles). Outside peaked at 26C with a dew point of 20C, which is quite impressive for UK standards. Not pleasant to work in though!

Hi Harry, I'm not quite sure what you mean - nearly all models have reasonable CAPE over the English Channel, SE England and East Anglia tonight?

I agree - for now the 00z AROME looks like a good bet for tonight's track. Storms tend to drift slightly further east than modelled (and tend to expand a little further east too). Will be interesting to see how it all plays out later today...

except for today maybe...

especially when the extensive cloud cover, which was well-modelled associated with the upper warm front, has little impact on any potential elevated instability tonight. I'm not quite sure where the strong signal for surface-based thunderstorms came from, one glance at forecast SkewTs reveals a very deep, saturated layer between 300mb and 550mb associated with this upper front, which has been bringing the outbreaks of rain so far (some evaporating in drier layers below on the way down to the ground). Any surface-based convection that did manage to develop this afternoon would only reach about 600mb, and so would be too shallow for any lightning in any case. The proper instability arrives behind this frontal rain, as the layer between 850-900mb begins to warm due to warm advection from the SE, while the upper levels cool as a shortwave impulse approaches from the south. Any activity tonight will be unaffected by boundary layer conditions and much more reliant on conditions aloft. Not promising there will be lots of activity tonight (in terms of areas affected) because that will depend on the increasing instability phasing with upper support, which is a lot harder to predict than when it is driven by surface conditions (such as sea breeze convergence etc, which are relatively easier to forecast). The instability plume will develop this evening across the English Channel and southern Britain, and will migrate gradually northwards through the night. Models tend to favour northern England with more widespread convection, primarily due to favourable phasing of the shortwave with the unstable profiles - but realistically the odd thunderstorm could develop just about anywhere in a rather random fashion, which the models will have a hard time pinning down.

a good example of the directional shear present right now - easterly at the surface, turning to a southerly aloft.

that shouldn't make any difference tonight since they'll be elevated thunderstorms

Indeed we do, balloons are sent up from Lerwick, Nottingham, Albemarle, Camborne, Herstmonceux, Valentia and Castor Bay. However due to cost-cutting, these are not as routine as they used to be (twice a day, at 00z and 12z) and often several are missing from each set. I believe our UK radar network is now all doppler, having been upgraded over the past few years - but sadly anything other than composite reflectivity is not available outside of the Met Office (not even for commercial purchasing).

No - the showery rain this morning has been well-signalled for a number of days to occur during Tuesday daytime, with any lightning (albeit isolated) most likely on the eastern flank closest to the best (weak) mid-level instability. A renewed pulse of instability will push across the English Channel this evening as the winds aloft begin to back more, and coupled with increased forcing from falling heights and the approaching shortwave, may lead to elevated thunderstorm development through the evening and night. The main thing that could scupper the storm chances tonight is if the models don't have a good handle on the subtleties of the upper pattern, and things may not overlap favourably - but we can dissect that as and if necessary at a later stage...

Heating over the UK is not particularly important today as most thunderstorm activity will be elevated, and won't really 'kick off' until this evening / overnight. The chances of anything surface-based are slim at best, and have never really been signalled strongly thus far.

agreed. Gusts of 40-50mph likely across East Anglia, perhaps locally 55mph. We usually get gusts in the 40s at least once every month throughout the year. Not a huge amount of rain expected today either, certainly not enough to recover the large deficit over the past few years.

Modifying today's 12z upper air sounding from Nottingham Watnall, to a representative surface temperature / dew point for mid/late afternoon over northern England, reveals 1,000 J/kg CAPE. Air temperatures of approximately 18°C required to break the cap and initiate convection ️

A slushy 1cm if you're lucky above 100m ASL, a little bit more over the Welsh hills / southern Pennines. Hardly anything at lower levels.

Worth noting that there is a suggestion parts of Cambs / Herts (especially over the hills there i.e. Stevenage-Stansted etc) could get a couple of cm from the showers feeding down from the north tonight. Perhaps 1-2cm locally in Norfolk/Suffolk on Saturday evening from North Sea showers too, but not expecting anything particularly widespread or disruptive.