Storms and Convective Discussion - 20th April 2019 onwards

[Harry]

1 minute ago, staplehurst said:

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

That’s very much the case here - elevated clouds tearing in from the S whereas fairly warm breeze it has to be said coming from the east

[StormChaseUK]

Near craven arms shrops. Not surprised if this turns active soon. 

[Cheshire Freeze]

PJB over on UKWW has lowered the risk tonight to low where storms are concerned. Admitting he thinks his original forecast is a bust on this occasion.

[Marko1690]

Cloudy all day in N.I, no heat from the sun all day, might just be a wash out instead of a lightning show.....

[Cheshire Freeze]

Why is it so hard these days to get widespread UK storms?? It's like if something can happen to prevent them, it will.

[The PIT]

A layer of nimbus stratus with the sun just visible and a few cumulus clouds scuttling along underneath. Wish it would rain would get those people who think everyone in the neighborhood wants to listen to their radio go inside.

[StormChaseUK]

Roads flooded now. Have stopped the car.

Tail end was very nasty to that rain area moving north over wales. 

[Harry]

This is PJB’s latest analysis:

This outlook from my perspective can now be lowered to a 30% LOW RISK across the region. There is too much cloud, and the frontal boundary is still far too active and there is a very large spread of cloud ahead of the frontal boundary itself limiting isolation and this has spread across the entire region. As the higher WBPT gets enriched into the frontal plume there may well be some growth from the medium layer cloud later this evening over Northern England, but the overall risk is now LOW.

Mother Earth wins this particular outlook against me !! Lol  

HRV Image showing the spread of cloud across the UK and the developing frontal wave and plume axis in the far SE of the Bay of Biscay and extreme northern Spain.

[P-M]

Some rapid shower development around the Bradford area moving north. Could it just be plain old rain or could it ignite. Only one way to find out and that's radar hunt.

[ChezWeather]

2 minutes ago, CreweCold said:

Why is it so hard these days to get widespread UK storms?? It's like if something can happen to prevent them, it will.

It seems that the only reliable place to see a storm in this country is the far SE, and that's only because of the close proximity it has to the continent. 

[Guest]

Just now, ChezWeather said:

It seems that the only reliable place to see a storm in this country is the far SE, and that's only because of the close proximity it has to the continent. 

Yes with tonight's activity looks less likely now the attention moves on to SE'ern areas where multiple models have a good handle on thunderstorms breaking out later tomorrow. Frustrating again but I will wait and see how tonight progresses.

[Flash bang flash bang etc]

I kept thinking the thick cloud across the country would hinder things, does this affect the MUCAPE for later though?

[shaky]

Think we can forget bout storms this evening!!just far too much cloud around!!ah well lets hope the end of the week delivers for us!!

[Cheshire Freeze]

1 minute ago, ChezWeather said:

It seems that the only reliable place to see a storm in this country is the far SE, and that's only because of the close proximity it has to the continent. 

There's a line in a song that goes, 'if I hadn't seen such riches, I could live with being poor'

The fact that a massive convective carrot was dangled in front of our noses for a couple of days, only for the set up to then become unfavourable, pixxes me off.

[Flash bang flash bang etc]

Meanwhile the write up for tomorrow just gets better and better (unless you’re flying an aircraft )

[P-M]

Not being funny but the Meto shifted their forecast and the warning doesn't even start until midnight. There's cells popping up all over now which fair enough may just be plain rain etc but while there's still a risk my glass is staying half full.  30% chance is still better than nothing yet already it's been written off. 

 

I've seen other forecasts that are still going for storms so not sure why anyone would write off the whole night at half 5 in the afternoon 

[Chris.R]

 I don’t understand the pessimism. Everything is elevated tonight so insolation or not has absolutely nothing to do with it. Still looks good to me. 

[IanR]

Not convinced about this , wasn't from about 12.00 this afternoon with a grayed out stratus overcast sky all day ,  doesnt even feel that warm in the breeze here,    

[TJS1998Tom]

2 minutes ago, Chris.R said:

 I don’t understand the pessimism. Everything is elevated tonight so insolation or not has absolutely nothing to do with it. Still looks good to me. 

I still think tonight has potential it's still early yet. Here we've had hazy sun all day with some blue skies. Clouded over now but not predicted anything till near midnight 

[Harry]

Indeed @P-M the plume is not due to arrive before 9pm so sit tight chaps! 

PJB is not infallible and I’m sure would be the first to admit when it comes to an unstable airmass anything can happen! 30% is much better than 0% so let’s see how it pans out. 

I’m also not feeling too despondent about this week - mass of instability sitting just across the channel and any subtle synoptic change will see it flood northwards.

[cheese]

3 minutes ago, Chris.R said:

 I don’t understand the pessimism. Everything is elevated tonight so insolation or not has absolutely nothing to do with it. Still looks good to me. 

This is my understanding too - nothing seems to have changed except the timing.

[oliverek7]

1 hour ago, zmstorm said:

BBC Weather has forecasted storms heading directly where I live Monday night and early Tuesday morning 

Same here I live south of London so I’m praying that is correct

[Allseasons-Si]

I have just been faffing around with the cam and still scratching my head as to what setting to film night time storms,what manual iso do i set it on?

cam is a sony DSC-HX60

type of sellection:-

superior auto

intelligent auto

scene selection

manual exposure

shutter priority

aperture priority

program auto

i have not faffed around with the cam that much,so help would be much appreciated.

[staplehurst]

14 minutes ago, P-M said:

Not being funny but the Meto shifted their forecast and the warning doesn't even start until midnight. There's cells popping up all over now which fair enough may just be plain rain etc but while there's still a risk my glass is staying half full.  30% chance is still better than nothing yet already it's been written off. 

 

I've seen other forecasts that are still going for storms so not sure why anyone would write off the whole night at half 5 in the afternoon 

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.

Edited June 23, 2019 by staplehurst

[Supacell]

A complicated picture over the next couple of days as it pertains to thunderstorm development. Outbreaks of rain are already occurring widely across SW England, Wales, the Midlands and NW England with some heavier bursts in what is currently a well capped, humid air mass. Later this evening an even more humid airmass arrives from the south along with a shortwave trough and at this point we will likely see some elevated destabilisation of the plume. As storms are expected to form above the boundary layer, CAPE charts at the surface are of no use when predicting how much energy these storms will be able to tap into. Likewise, surface conditions such as temperature and how much sunshine has occurred in the day will have no bearing either. It is the parameters higher up we need to look at. Although, this being said, tonight does not look as conducive to big storms as it previously did.

My map shows 3 main risk areas amongst a more widespread grey box which is there as in my view there is a chance a storm could pop up almost anywhere over the next couple of days.

The blue box is for tonight's heavy showers and elevated storms rumbling north overnight. The first signs of thunder would probably be over mid-Wales and the West Midlands later this evening before heading into NW England by midnight to join with further heavy showers and thunderstorms that will have by then developed across the north of the Midlands into Northern England. As these move north into Scotland towards tomorrow morning they will lose any electrical activity they do have, but still produce a lot of rain well into Monday with a flooding risk to the north of the blue box.

The purple box is for a more potent area of storms that could develop tomorrow. There is some model divergence on whether these develop but if they do then there is a risk of severe thunderstorms and these could bring the risk of large hail and gusty winds. NMM has over 2000j/kg of MUCAPE to be utilised along with 20-25 knots of deep layer shear. I have put the time on as from 00z Monday as in my opinion there is also a slightly higher risk of storms overnight across Lincolnshire and East Yorkshire than what there is in the wider blue box.

The orange box is relating to what will likely be the strongest storms of this 2 day period, which will be crossing the channel, possibly as an elevated MCS, from France later tomorrow. Please note there is still uncertainty as to where this will be and my box covers the most likely area. In reality, it could miss the UK entirely and head through the Low Countries, it could be further west which would then bring the Midlands into play too. However, it is likely that most of the thundery activity will be on the eastern side of the system whereby it engages some very high MUCAPE, but on its eastern side there could be severe storms with very frequent lightning, large hail, gusty winds and torrential rainfall of 40-60mm/hr. This will need watching tomorrow and I have already booked off Tuesday in preparation for a storm chase on Monday night.

Edited June 23, 2019 by Supacell