Storms and Convective discussion - April 2024

[viking_smb]

00z was a occluded front (on previous fax) now its just a warm front for thurs 00Z

 

[Andy Bown]

 viking_smb a plume of unstable warm air then hopefully! 

[Eagle Eye]

Convective Outlook️ 

Tuesday (not the Wednesday one yet) 

During Tuesday early hours, a low pressure will approach from the aouth of Ireland introducing heavy & intense rain across S parts of Ireland which would of cleared North by the early morning period across Northern Ireland. The odd isolated lightning from this front cannot be ruled out throughout the early hours of Tuesday.

 

Heading into the early morning period, we are expecting to see an increase of Cape of anywhere from 100J/KG-400J/KG across S parts of Ireland with intense showers increasing in activity. This may bring the odd one or two thunderstorms in the morning across S & SW parts of Ireland, however lightning will mainly remain isolated & sporadic.

 

Into the late morning/early afternoon, Cape will drastically become more widespread mainly across the AOI "Area Of Interest" Zone up to 300J/KG - 600J/KG which will increase the risk of lightning across Ireland. We are interested that Cork up to past Galway will see the most activity within Ireland. This risk will continue into the evening, with further sporadic lightning expected, however one or two thunderstorms may develop for a time.

 

Looking at the late afternoon/early evening period, were expecting to see a convergence line form dangling down across the Central spine of North England down to just East of Birmingham. Heavy & intense showers are expected to from of from this alongside with Cape around 100-300J/KG which may allow a few lightning strikes to occur. Confident remains low on if any lightning will occur, however there is a risk.

 

Into the late evening/ night time period, the risk of heavy showers will head north clipping parts of Cornwall which may bring a few lightning strikes due to Cape around 200-400J/KG, however confident is quite low on this.

 

Our attention then shifts towards parts of South East England into East Anglia, where surface based thunderstorms are expected to develop across NE France where 500+J/KG sits which these storms will advect north towards extreme eastern parts of East Anglia. These thunderstorms are likely to become elevated throughout its course north. There is a low risk of it slightly being further W than expected clipping E England & SE England, which is why a low risk covers these areas just in case. There is also a chance these storms may not end up clipping EA. Great Yarmouth looks to have the greatest chance of seeing elevated thunderstorms throughout  the night.

[viking_smb]

@Eagle Eye ECM is chopping and changing at mo, I've noticed it has moved south and less intense, but I expect it to chop and change and more likely move back east

[Eagle Eye]

Convective Outlook️ 

Wednesday (day 2)

Wednesday night a shortwave trough advancing east of a frontal system should allow for storms to form over northern France potentially moving NW into southern parts of England. There are however uncertainties over positioning still so much so that they could instead be centred over Belgium and move into eastern parts of England, slowly weakening moving NW/W into the midlands. This is limiting the confidence over where to place the risk currently given lots of difference between the models. However, away from the modelling issues, this a high-end potential event but with a few bust risks as most do to be discussed later.

A theta-W ejection from mainland Europe will either be centred over Germany and move NW into Belgium or further west on the border between Germany and France and hit northern France, and storms will likely initiate in one of those two areas. As they do, large upscale growth by deep-layer shear is likely into an MCS is likely with forcing being very high compared to a typical risk becoming very favourable for clustering into a system of storms, unless there's a downtrend in the forcing, this seems a very likely solution. Given the high theta-W airmass and surface inversion that appears to hold in place, a transition to elevated storms towards the evening as surface energy over northern France and/or the border and Belgium area weakens appears likely. With the remaining mid-level energy appears to be high as these storms move into a new area of what appears to be separate energy held in the mid and upper levels of the atmosphere slightly further north in the late evening. And this is where the transition upscaling into an MCS appears likely as well.

The initial surface based convection over land becomes its own system as the trough forms with dry air undercutting the trough and driving the band of moisture convergence, influxing energy towards the trough itself and taking in energy from the surroundings. It's a very important part of the MCS development and also the potential to survive the channel, without the moisture convergence becoming centred around the developing trough, or becoming centred too early, it won't reach the UK. Currently most models are adamant that despite the multitude of scenarios with timing possible, the trough develops just late enough into the evening for the MCS to develop as an elevated MCS, rather than surface based and what shows that is that on some models without the whole storm being forced along the trough, the parts not on it fall apart as the surface energy weakens. 

This trough also brings in significant ascent beyond the boundary layer with buoyancy more typically associated with surface storm days in the height of summer with -5 LI's at the 850 hPa height. Therefore any convection could well force a vigorous updraft capable of significant hail just past an inch in diameter but mostly limited to that given the strong low-level shear in place that will take away some of the hail's strength. So despite favourable hodographs with a strong inflow region, along with widening updrafts because of combining cells and energy strong enough for quick updraft speeds, the hail is still limited to the lower end of the severe potential. This forced ascent should also help with quick upscale growth once the shortwave trough helps rapidly increase it and therefore most surrounding cells will be brought into the MCS likely as constructive mergers for momentum inducing events, so watch out for larger hail and more significant storms where these mergers take place, should the storms reach the UK (assuming they form which looks very likely despite the capping in place) and a small tornadic chance but the elevated nature of the MCS will likely keep that very minimal.

Surface energy may still linger crossing the channel on the eastern side of the trough, along with strong deep-layer shear becoming more guided towards a hook there as well. This has lead to 50+ J/KG of 3CAPE with 1000+ J/KG of MUCAPE possibly forcing a Supercell for a time on the eastern side of the MCS or detached from the MCS itself, risking stronger hail and again a small tornadic chance. There could also be an elevated Supercell linked in with the actual MCS itself. The hodographs are fairly favourable for that, the actual MCS upscaling is more of an ascent nature than a speed shearing nature.

400+ (m^2/s^2) of SRH certainly shows the significant potential of this event but that depends on the shape of the hodograph which varies a lot from model to model as they tend to do at this point in the forecast. The higher end do have a very Supercell and hail favourable highly streamwise flow with a large inflow region though. However, there's still a weak tornadic potential with the surface lift just not being conductive on almost all models as the surface based Supercell looks very unlikely, just a small potential, most likely elevated if one does form.

Lightning risk does look to exist fairly well with this, saturation doesn't seem much of an issue aside from a few areas on soundings. It's not great but strong energy and often I find lots of momentum builders as there are in MCS's can counteract that as long as there's enough energy, there does seem to be some sort of threshold past about 1,000 J/KG where the saturation can become less of an issue. This is mostly based off experience and modelling though. Saturation does appear to be quite good on the central southern coast on the models that go for the northern France initiation and also the ones that go for a Belgium initiation, hence that is the highest risk for lightning at the moment on the models.

The more widespread lightning event currently modelled appears to be the Belgium initiation that the ECM is currently adamant on, but an uptrend in the northern France risk wouldn't take much to do the same. There's a fairly high-ceiling for this event, but it's still complicated in it's expected evolution and the surface based storm transition to elevated timings. Saturation could also become more of an issue if the models start trending that up. 

[viking_smb]

 Eagle Eye thanks eagle eye, you have calmed my nerves a bit  

[viking_smb]

 Eagle Eye regarding that trough current fax (00z thurs morning) has it between belgium and kent, but as you said it could be a bust

Edited April 29 by viking_smb

[The Tall Weatherman]

@Iceman2606 I saw the same hailstorm yesterday as well, the rainbow and Mammatus at the end were lovely !

[Eagle Eye]

A sounding for Wednesday night. Fairly tall storms, that's what roughly 30,000 feet possible? Along with a hooked deep-layer shear with more than enough inflow for severe hail when considering it with the MUCAPE. Very interesting to keep an eye on Wednesday night's event with our first real big plume of some sort of variation this year i'm pretty sure.

 

[Eagle Eye]

00Z UKV update, but there's still a lot of chopping and changing on the models going on. 

[Eagle Eye]

UKV 03Z upgrades it and has a signal it doesn't want to change. However, we'll see if the other models give in to this signal or not of the direction of travel. 

Edited April 30 by Eagle Eye

[Petorious]

50 miles more north please  

[ChezWeather]

@Eagle Eye your forecasts are so appreciated. Keep it up, amazing work

[Andy Bown]

 Eagle Eye do you think the first cluster (around 22.00 in Dorset/Wiltshire) will be thundery? Or just the second lot that arrives later in the night? 

[Rush2019]

European storms have put their outlook out now, to include the early hours of Thursday morning.  More parts of the UK now within a risk area.  May see something a bit further North, perhaps.

[weatherobsuk]

I'm tempted to head out in the new car and chase this one as it feels like a millennia since there's been any significant storms here in the NW, a more northerly component in the models would mean setting up somewhere in Norfolk but somewhere along the southeast coast is looking likely (assuming there's no MWay closures to get there.) Otherwise it'll be webcam watching and hoping something closer to home pops off towards the South Midlands.

[Rush2019]

Here's UKVs current look at the precipitation at a glance, 11pm Wednesday and how it looks at 3am Thursday.

[Eagle Eye]

 Andy Bown

The first part is just frontal rain so I don't expect it'll be thundery but the second one should be if it does play out like that. 

[ChannelThunder]

UKV has woken up overnight, then! Just about keeps me in the game but one northward shunt and it's game over. 

[Eagle Eye]

Given the really bad modelling of this, I probably won't be issuing tomorrow nights risk till tomorrow afternoon. I'll just be doing tomorrow's small daytime risk tonight. 

[Azazel]

Wonder if it'll arrive before i go to bed - would keep up the tradition here of elevated storms in May.

[A Face like Thunder]

An unusual scenario for Wednesday into Thursday. Warm air on an Easterly from the Continent meeting cold air from the W/SW. Normally you would expect it to be the other way round, wouldn't you?  

[Eagle Eye]

AROME appears to support the UKV fairly well.

[ChannelThunder]

 Eagle Eye similar weather, very different timings! Let's hope UKV has the timing right, because it's a work/school night after all! 

[LightningLover]

Very impressive reservoir of MUCAPE on the AROME as well- let's try and get those purple colours over here!!