Storms and Convective discussion - 20th March 2023 onwards

[Sparkiee storm]

Some of the convective skies around Walsall yesterday.

 

[A Face like Thunder]

Rumble of thunder at 12 noon and heavy showers all day so far. Not a day to be out in! 

[Jamie M]

Nice to see the convection around

[alexisj9]

30 minutes ago, Jamie M said:

Nice to see the convection around

Yep, had a heavy shower come through here not long ago.

[Arnie Pie]

18 hours ago, WeatherWatchmanG said:

Did anyone else have the most vivid rainbow they've seen in a long time today? I didn't have any cameras handy but it was very bright.

Yes... some beauties around our way

this screenshot from yesterday doesn't really do it justice

[Robbie Garrett]

Looking NNE

[CoventryWeather]

Know it's not convective, but a nice rainbow to end what's been a dry, warm day. 

[Eagle Eye]

Convective Outlook

 

Sat 25th 21:30 - Sun 26th 17:00

 

With a low pressure pushing through early morning whipping up quite strong winds on the south coast there may be some embedded convection within the low but the exact tracking of it is debatable.

 

Behind that there appears to be an occlusion between SW England and Ireland which might spark 200 J/KG of SBCAPE with daytime heating perhaps best along a PV lobe in central Ireland but not strong enough for an AOI as of now. A cold sector along the central south and south east will likely mean buoyancy and CAPE won't get strong enough for much lightning similar to further north despite there being a rash of showrs likely through the UK, the height of the clouds are unlikely to get high enough for lightning away from the SW of England and Ireland.

 

Shearing may be best along the cold sector parallel to the eastern sector of the M4 corridor but that's where CAPE is unlikely to be taller than a few joules which will really struggle to create anything at all. Though the shearing tends to lag behind slightly on the occluded front and cold sector so moderate (35 knots)  shearing earlier on in the afternoon is still quite possible for some taller storms so best lightning potential is between about mid day and 4PM from the afternoon showers as they tend to be.

 

The saturation is likely to be less of a problem than previous events but kinematics such as buoyancy are only moderately favourable so lightning is still likely to be relatively infrequent even in the strongest storms. Though the lapse-rates are even more favourable than before so hail a few CM's big given small low-level shear.

 

So hail and infrequent lightning are the main possible risks in the storms but only really in the strongest areas.

 

 

[Eagle Eye]

Already off to a better start storm wise than last year. 6 slight risk forecasts issued in March compared to last years 3 in March by Convective Weather.

Edited March 27, 2023 by Eagle Eye

[Windblade]

Rest of the week we have lows coming in from the Atlantic I believe. I wonder if there's any chance of some stormy stuff mixed in with these? if not I'll just enjoy the heavy (hopefully) rain. 

[Eagle Eye]

Tomorrow is a sleeper type risk. Could go either way. The cloud cover and frontal setup may initially not look amazing but there's arguably the most supportive environment in Ireland that there has been this year but the bust factor is quite high. I do expect a few showers/thunderstorms to get going despite the cloud cover though.

Lapse-rates are decent suggesting fairly buoyant air and perhaps some hail risk as well.

Lifting at the surface is likely to be quite good despite the cloud cover. Likely due to how strong the cold front must be because as the temperature difference between the temperature of  an air parcel and the environment surrounding it increases so does the buoyancy of the air.

Similarly, the 850's become quite buoyant towards mid-late afternoon (ish).

So, into the evening looks good for the Irish Sea and Ireland especially though the SW and Wales may have a good setup as well.

Deep-layer shear loosens to the west of Ireland towards towards the mid-late afternoon but holds in the east so more organisation likely in the east the later you go into the afternoon, the worse it gets for the West of Ireland and the best it gets for the East of Ireland.

That said low-level shear is remaining quite strong so cells may be able to keep up in the West of Ireland longer than just popups but eventually may turn into more of a crud.  Also supports some tornadic potential and weakens hail potential.

Supercell chances look fairly plausible.

SBCAPE in excess of 500 J/KG.

Sig tor parameters are there apparently..

My quick look in from earlier today for that setup. Oversaturated in the crud area and Ireland but slightly less so. Also a risk for the SW and Wales if the diffuse cold front and cold front scenario can work favourably.  Dry nose ridge in Northern Framce as well. Would work well as a daytime plume cap in the Summer to stop Northern France storms from 'eating up' SBCAPE.

Here's the breakdown of the event via a sounding in Northern Ireland.

Note that most sig tor critical angles are 90° + and most tors tend to be 50° + so it's just below.your typical small tornado Risk but there's a chance.

So then mostly a multicellular risk given straight NE'wards deep-layer shear compared to horizontal deep-layer shear typical for Supercells.

Edited March 28, 2023 by Eagle Eye

[ChannelThunder]

Tomorrow evening's UKV:

[Eagle Eye]

UKV you good there?

[Metwatch]

5 minutes ago, Eagle Eye said:

UKV you good there?

Looks like that was the previous 12z run, 15z on TWO less potent, but a direct hit for @Jamie MM if it verified. 

[ChannelThunder]

Seems *far* too early in the year to have any significant night lightning, but I guess we'll see. Looking forward to seeing Dan's outlook in the morning.

[Eagle Eye]

13 minutes ago, ResonantChannelThunder said:

Seems *far* too early in the year to have any significant night lightning, but I guess we'll see. Looking forward to seeing Dan's outlook in the morning.

Same. I've got a few paragraphs on it to say the least. Speaking of...

Convective Outlook

Wed 29th 07:00 - Wed 29th 21:00

A warm front followed by a diffuse cold front will set the scene for an Irish based risk Wednesday afternoon with a slightly increased chance for storms in SW and Wales on Wednesday evening.

A squall line associated with a stronger cold front behind those will swing by Ireland in the morning and behind it instability resides in a pool of moisture. Though thick cloud cover from highly saturated low-levels may initially inhibit deep convection, I think the amount of MUCAPE available to be used up will likely be around 500+ J/KG in the strongest areas. If cloud cover can clear in places then 550+ J/KG of SBCAPE and nearly 1000 J/KG of MUCAPE may be available especially across central and northern areas of Ireland with the AOI there.

Strong lift aided by the strong cold front passing through will be able to provide ample buoyancy in the atmosphere for deep convection potentially up to 20,000 feet or taller in the areas of best kinematics. Lapse-rates may also be supportive for hail but we'll discuss that later.

The Ireland risk comes mainly later on in the afternoon with the weakening of cloud cover with the cold front far enough away now. Latent heat release may increase buoyancy again despite it weakening as the cold front gets away and that should provide the best low-level ample lift for the strongest storms to form. This will be the area of deepest convection potentially reaching up to near 25,000 feet given strong shearing and the saturation in the updrafts decrease given 40 knots of 6km shear forecasted in parts of Northern Ireland with a multicellular mode most likely. Though saturation does look to stay fairly high so its hard to tell for now unless a Supercell can arise then it's likely that the updraft and moist layers I the atmosphere will to separated. Organisation of lightning is possible as long as the low-levels don't keep being overly saturated.

The weak vorticity inflowing on the hodographs does look to be streamwise and with the fairly good looking low-level hook a tornado certainly cannot be ruled out. Though the critical angle forecasts and storm modes tend not to support one we cannot just ignore the hodographs showing that hook like shape and moderate low-level shearing so there is some tornadic potential. SRH is looking to be quite low (between 100-200 m²/s²) but it can often hide the amount of SVC into a thunderstorm.

The strong low-level shearing will likely counteract the lapse-rates and quite cold upper air to weaken the hail risk across Ireland but not fully. Some hail risk will still be possible, just unlikely to be large.

NE storm motion with straight cell motion will mean that multicellular modes will mostly have popup storms that will be replaced with changes in saturation based off the storm itself change of saturation at low-levels I would imagine. Multiple multicellular modes are plausible though fairly small themselves.

Supercellular risk is mainly in the AOI area in Ireland and Northern Ireland and is mainly conditional that the deep-layer shear is straighter on the hodographs than currently forecasted which tends to be on the southern side of the multicellular risk but we'll have to see.

Towards mid-afternoon and into the evening the shift slowly focuses towards the south coast and Wales. With a plume of Theta-E advection on the southern side of the same cold front for Ireland and unstable air in a moderately sheared area given warm SST's for this time of year and the cold upper air. Heat release under cloud cover is unlikely to be as quick with the warm sector behind the warm front clearing at the 850's hPa levels and therefore quick heat falling at those levels will allow for late afternoon to start sparking thunderstorms in the North Atlantic North of the Bay of Biscay and just west of Brittany which will likely cluster up into a mass of heavy rain. Towers of vorticity maxima and convergence are likely to supply the best chance for lightning between the SW and Wales but the UKV also shows some sort of storm complex pushing along the whole south coast with less clustering up and therefore able to maybe keep its strength on some of the runs.

A typical plume situation but given the time of year, lightning is unlikely to be frequent and lapse-rates are quite unsupportive of anything really. Supercells have very little favour given the setup and the forecasted hodographs but a small chance though hail is very unlikely.

An area of interest has also been added here where it appears that lightning is most likely though truthfully it may get frequent enough anywhere through Wales and the South Coast. The midlands may get a strike or two according to the UKV but not many other models show it as well.

The south/southeast may get an upgrade closer to time given that there will be very little interference pre best plume axis from northern France surface based Storms compared to other plume events given the ridging in place in the day that weakens as the day goes on. However, the time of year and the lack of supportive modelling keeps it at a low risk.

Overall, these storms will be capable of small hail, heavy rain, moderately frequent lightning, some tornado potential and a chance of a Supercell or two.

[CoventryWeather]

2 hours ago, ResonantChannelThunder said:

Tomorrow evening's UKV:

Looks like a band of heavy rain - probably a bit of thunder mixed in at times.

The 18z looks better for some storms across the south coast, with a lot of elevated showers at 6/7, but I'll be interested to see what Convective Weather says. 

[LightningLover]

1 hour ago, ResonantChannelThunder said:

Seems *far* too early in the year to have any significant night lightning, but I guess we'll see. Looking forward to seeing Dan's outlook in the morning.

Distinctly rare, but entirely possible to have more organised thunderstorms in Late March- I believe 23rd March 2005 was a great example, when elevated thunderstorms formed on the periphery of mild air being wafted up by a deep trough out west... 850's were only around 6-8c, but it did the job! Obviously they weren't May-September grade storms, but still!

Edited March 28, 2023 by LightningLover

[ChannelThunder]

52 minutes ago, LightningLover said:

Distinctly rare, but entirely possible to have more organised thunderstorms in Late March- I believe 2005(?) was a great example, when elevated thunderstorms formed on the periphery of mild air being wafted up by a deep trough out west... 850's were only around 8-10c, but it did the job! Obviously they weren't May-September grade storms, but still!

Good to know it's happened before, then! Sounds like that was a similar set up, too. 

[LightningLover]

2 minutes ago, ResonantChannelThunder said:

Good to know it's happened before, then! Sounds like that was a similar set up, too. 

Yeah just found it on Meteociel; Slightly more southerly component on the wind direction as you can see, but very similar, and the uppers were actually cooler than tomorrow's!

[East_England_Stormchaser91]

59 minutes ago, LightningLover said:

Distinctly rare, but entirely possible to have more organised thunderstorms in Late March- I believe 23rd March 2005 was a great example, when elevated thunderstorms formed on the periphery of mild air being wafted up by a deep trough out west... 850's were only around 6-8c, but it did the job! Obviously they weren't May-September grade storms, but still!

I seem to remember late April 2004 I believe, I was awoken to some very good night storms heading NNE. I never had the fortune of being able to access radar back then, but they were very decent so early on in the season!! Still sticks in the memory. Followed by a lovely, warm day after too. 

[LightningLover]

Just now, East_England_Stormchaser91 said:

I seem to remember late April 2004 I believe, I was awoken to some very good night storms heading NNE. I never had the fortune of being able to access radar back then, but they were very decent so early on in the season!! Still sticks in the memory. Followed by a lovely, warm day after too. 

15th April 1981 was also spectacular apparently (was only a twinkle in my mum's eye then); Warm uppers were advected WNW from France by high pressure, with a resultant prolific mid-level lightning show... But interestingly  only 5-7c at the surface here with fog and a keen NNE breeze!! 

[East_England_Stormchaser91]

Just now, LightningLover said:

15th April 1981 was also spectacular apparently (was only a twinkle in my mum's eye then); Warm uppers were advected WNW from France by high pressure, with a resultant prolific mid-level lightning show... But interestingly  only 5-7c at the surface here with fog and a keen NNE breeze!! 

Wow, that must’ve been spectacular. Most of our amazing storms here are governed by the dynamics in the elevated layers. 
Correction from earlier post, it must’ve been April 2005 when those storms passed through! Just looked at the charts archive! Was a very good setup indeed. 

[Eagle Eye]

9 minutes ago, LightningLover said:

15th April 1981 was also spectacular apparently (was only a twinkle in my mum's eye then); Warm uppers were advected WNW from France by high pressure, with a resultant prolific mid-level lightning show... But interestingly  only 5-7c at the surface here with fog and a keen NNE breeze!! 

Convection and buoyancy can theoretically be linked and all you need is a big temperature change in the environment I assume vertically or horizontally. You also need moisture and the parcel of air to be unstable which comes from the air parcel being warmer than the ambient air. Moisture is a big limiting factor in Winter and early Spring. Theoretically temperature doesn't matter but in practice it will do with an island with relatively limited temperature differences like ours.

Edited March 28, 2023 by Eagle Eye

[LightningLover]

Here's the charts for the 16th April 1981. You can clearly see the little low near Spain driving things in the upper levels, whilst the high pressure kicks up a stiff NNE wind sourced from Scandinavia! Fascinating setup that highlights how we can dissect the different layers and dynamics.