Storms and convective discussion - 18th June 2020 onwards

[Zak M]

Convective Weather

WWW.CONVECTIVEWEATHER.CO.UK

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Forecasting thunderstorms and severe convective weather across the British Isles and Ireland for up to the next 5 days.

Convective Outlook

VALID 06:00 UTC Sat 25 Jul 2020 - 05:59 UTC Sun 26 Jul 2020

ISSUED 22:30 UTC Fri 24 Jul 2020

ISSUED BY: Dan

A sharpening upper trough will swing northeastwards across the British Isles on Saturday, the trough axis located over Ireland at 15z, SW Scotland - SE England at 21z and clearing to the North Sea by 03z. The associated cold pool will create an environment with steep mid-level lapse rates, this most pronounced close to the trough axis. This ultimately means the most unstable environment will be over Ireland during the afternoon / early evening, migrating eastwards across England and Wales during the evening and night hours.

... IRELAND / NW + W WALES / NW ENGLAND / SW SCOTLAND ...

A shortwave will track eastwards during the afternoon hours, and this will provide the main focus for scattered showers and thunderstorms developing. The rather most airmass suggests cloud could be rather extensive, but there should be increasing breaks with each passing hour during the afternoon. Shear is a little meagre, generally 15-20kts and fairly unidirectional suggesting rather pulse-type mode most likely, and despite rather saturated profiles 400-900 J/kg CAPE should be sufficient for sporadic lightning, especially across southern and eastern Ireland. Hail 1.0-1.5cm in diameter and gusts of 35-45mph may be possible from the strongest cells.

Showers and thunderstorms will then drift eastwards across the Irish Sea during the evening hours into W / NW Wales, SW Scotland and NW England.

... SCOTLAND ...

Morning rain may contain some embedded weak elevated convection, and while a few isolated lightning strikes may be possible the risk is considered fairly low. Increasing insolation by the afternoon will likely yield 300-600 J/kg CAPE, primarily Aberdeenshire and to a lesser-extent Angus and Caithness. A few scattered heavy showers are possible here, with the risk of a few lightning strikes (especially Aberdeenshire). The slack surface pattern and associated low-level convergence vorticity may produce one or two funnel clouds.

... ENGLAND & WALES ...

On the forward side of the upper trough, broad divergence aloft will encourage fairly widespread lift and this in proximity to a frontal boundary is likely to result in a frontal wave developing in the vicinity of the English Channel into SE England, particularly during the afternoon hours. The extent of this frontal wave is naturally handled differently amongst various NWP guidance, with the 12z/Fri ECMWF perhaps the most bullish covering most areas from the Bristol Channel to the Humber southwards. Even if the precipitation is not this widespread, there will likely be a substantial high cloud shield to the north of the main area of precipitation, and this will ultimately impact the amount of surface heating of the rather most airmass (dewpoints 15-17C). Even if deep convection manages to develop in the afternoon, the warm bulge in the mid/upper levels will likely suppress the depth of convection somewhat until the evening hours when cooling aloft occurs as the upper trough approaches. 

That said, a small window of opportunity may exist around midday/early afternoon in the Cambs/Lincs/Norfolk vicinity before increasing cloud dilutes insolation and reduces surface temperatures.

Otherwise, it may be the evening hours that offer the best potential for deep convection and heavy showers / a few thunderstorms. One or two pronounced SW-NE convergence zones may develop, the lines of showers then migrating generally eastwards with time while individual cells track to the NE. Shear will be stronger here under the influence of a mid-level jet, and 30-40kts DLS may aid in cell organisation and longevity - especially across southern and eastern England. Hail up to 1.5cm in diameter may be possible, alongside gusts of 35-45mph. Activity may persist / keep developing until the early hours, before finally clearing to the North Sea.

Given the uncertainty with regards to the frontal wave, we have refrained from issuing a SLGT at this stage but it is likely one may be introduced if confidence increases a little (primarily S / SW England to London, and the C / E Midlands to Lincs/Norfolk).

[The PIT]

Local forecast agrees it's a dead duck with light showers in the morning then dry and cloudy.

[Thunder and Lightning]

I'm happy about this slight in the South and South-East

Convective Weather

CONVECTIVEWEATHER.CO.UK

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Forecasting thunderstorms and severe convective weather across the British Isles and Ireland for up to the next 5 days.

 

[Argyle10]

Reckon there will be a chance for me today? 

[Dreckly]

27 minutes ago, Charlie Harnett said:

Reckon there will be a chance for me today? 

Looking possible

[Argyle10]

Just now, Dreckly said:

Looking possible

I m right on the edge of it though so I doubt but you are in it? You will probably get something not me

[Dreckly]

2 minutes ago, Charlie Harnett said:

I m right on the edge of it though so I doubt but you are in it? You will probably get something not me

Yes I'm in it, you never know though you could get some even on the edge.

[Argyle10]

Just now, Dreckly said:

Yes I'm in it, you never know though you could get some even on the edge.

Very true but I never get storms here

[Dreckly]

1 minute ago, Charlie Harnett said:

Very true but I never get storms here

Fingers crossed 

[Argyle10]

10 minutes ago, Dreckly said:

Fingers crossed 

[Flash bang flash bang etc]

Surprisingly good odds today for our area - and for once right in the middle.

 

Forever the pessimist (a well seasoned one because of the common bust factor in these parts) I can’t read risk forecasts without looking for the alert words ‘sporadic’, ‘unlikely’ and ‘meagre’ - amongst others - which has left me unsure as to the potential in the real terms this afternoon.

CW uses the word ‘sporadic’ a couple of times and in general the risk seems low for anything half decent. However UKWW released a forecast with some very flowery language including ‘severe’ and  ‘supercell’ and on the whole it seemed a lot more positive.

So I’m really not sure which way to lean, but I just can’t let myself get excited about it, barely 10% of these forecasts materialise (for this area) and I’m not prepared to chase today. Not knocking the forecasters - who are doing their best - just the synoptics which always collapse just before things fire up.

Wont be holding my breath, but will keep an eye on the radar

[Spikey M]

Well if this cloud and drizzle doesn't bugger off I can't see anything happening.

[Frosty hollows]

Some beefy looking squall lines developing but yes, need  a decent spell of insolation before I'll get my hopes up 

[Mapantz]

I'll believe it when I see it.

Quite varying forecasts today..

[Argyle10]

49 minutes ago, Dreckly said:

 

Met office yellow warning

[Jamie M]

3 minutes ago, Mapantz said:

I'll believe it when I see it.

Quite varying forecasts today..

Nothing forms when the Met Office issues a thunderstorm warning. 

[Argyle10]

51 minutes ago, Dreckly said:

 

Quite a high possibility too

[Spikey M]

9 minutes ago, Mapantz said:

I'll believe it when I see it.

Quite varying forecasts today..

We've gone from the heart of the severe storm warning to not in it at all. Fantastic.

[Argyle10]

59 minutes ago, Dreckly said:

 

(Sorry can't figure how to get the reply bit off sorry) 

[Jamie M]

Had a friend send me a picture of the cloudscape near Worcester. It's impressive.

[Sparkiee storm]

Heavy showers over the Midlands already, good signs for later maybe?

Edited July 25, 2020 by Sparkiee storm

[StormLoser]

Hmm. We seem to have gone from a dead duck to an active warning in just a few hours. The problem is, almost everyone has a different take on it!   

I'm amused at receiving an e-mail from the Met Office warning of thunderstorms in the South East, only to find what I would call the South East is actually not in the warning area (rolls eyes). I do wish they'd improve their region definitions.

Looks like we'll get some rain today. That's for sure.

[Argyle10]

Just now, Sparkiee storm said:

Heavy showers over the Midlands already, good signs for later maybe?

At least you've got breaks in the cloud, just persistent low cloud here lowering my hopes for anything

 

[Paul Sherman]

15 minutes ago, Spikey M said:

We've gone from the heart of the severe storm warning to not in it at all. Fantastic.

Pretty much standard nowadays

We get the 24-27c all week whereas areas further North have been in the mid teens and we get squat and they get the goods, its the standard default for the last 10 years.

Moving on to August

[Ben Sainsbury]

I do have an eye on developments across Somerset/Devon into Dorset around 6-7pm this evening. Almost all the models have converged on a potent line of storms tracking eastwards and show the most significant precipitation rates of the day here. Check EURO4 out for an example:

Don't often see rates like that shown for the UK.