Storms and Convective discussion - 25th July 2021 onwards

[Had Worse]

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MARINES-HELIOS.PAGESPERSO-ORANGE.FR

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Résidence hôtelière** LES MARINES D'HELIOS est située à 200 mètres de la plage au bord de la Mèditerranée, composée de villas individuelles jumelées avec terrasse extérieure , piscine avec petit bain, tennis...

 

[A Face like Thunder]

To my surprise, I see there is a yellow weather warning in place for rain covering much of England on Sunday. I could see a problem tomorrow on the NE coast with rain in view of a trailing warm front, but not after that and not over a widespread area. Any thoughts?

[staplehurst]

1 hour ago, A Face like Thunder said:

To my surprise, I see there is a yellow weather warning in place for rain covering much of England on Sunday. I could see a problem tomorrow on the NE coast with rain in view of a trailing warm front, but not after that and not over a widespread area. Any thoughts?

Same frontal boundary stalled over eastern England on Sunday providing the focus for convergence given light surface winds. Less ridging aloft will allow deeper convection on Sunday, which with high precipitable water (~33mm), weak steering flow and potential for backbuilding along the same line could result in local flash flooding. There may also be some upscale growth as the front reinvigorates on Sunday night, which will just add further water on already locally flooded ground. Some high-res models have >60mm just on Sunday daytime, without taking into account further persistent rain during Sunday night (that's assuming the front remains in situ and doesn't wriggle about to the east etc). Very fine margins as to which areas receive the heavy rain.

Edited September 17, 2021 by staplehurst

[A Face like Thunder]

36 minutes ago, staplehurst said:

Same frontal boundary stalled over eastern England on Sunday providing the focus for convergence given light surface winds. Less ridging aloft will allow deeper convection on Sunday, which with high precipitable water (~33mm), weak steering flow and potential for backbuilding along the same line could result in local flash flooding. There may also be some upscale growth as the front reinvigorates on Sunday night, which will just add further water on already locally flooded ground. Some high-res models have >60mm just on Sunday daytime, without taking into account further persistent rain during Sunday night (that's assuming the front remains in situ and doesn't wriggle about to the east etc). Very fine margins as to which areas receive the heavy rain.

Thank you staplehurst. I meant to say Sunday rather than Saturday for the rain on the NE coast, but I still do not see why such a wide area of England is covered by the yellow warning.

[Andy Bown]

2 minutes ago, A Face like Thunder said:

Thank you staplehurst. I meant to say Sunday rather than Saturday for the rain on the NE coast, but I still do not see why such a wide area of England is covered by the yellow warning.

Because they and indeed nobody has any idea where the front will be. Until 3 days ago a cold front was expected to cross the whole country today. It’s still barely into the far West.

[BrickFielder]

Maybe an opportunity for some lively showers Bristol and Cardiff areas late afternoon today which will trundle north east. Weak upper level band of cooler air aloft drives the risk, but cannot really see storm development.

Tomorrow late afternoon looks like storms could be possible for Ireland ,West Wales and Cornwall as cool air aloft arrives. Whether storms develop and where is very much down to timing of the movement of the fronts. Still not impressed with the. storm potential but mid level lapse rates are better than todays. Weak winds will tend to limit storm severity and heavy showers seem more likely than storms from current weather modelling. UKV model is noted as showing a slightly different evolution of precipitation.

 

 

[MP-R]

I did indeed get a sharp downpour late this afternoon leaving a few mm in the gauge. Made a nice change.

[Jamie M]

CW Outlook

Day 1 Convective Outlook

VALID 06:00 UTC Sun 19 Sep 2021 - 05:59 UTC Mon 20 Sep 2021

ISSUED 07:49 UTC Sun 19 Sep 2021

ISSUED BY: Dan

The main focus on Sunday will be associated with slow-moving heavy downpours in east/southeast England. Low-level convergence is expected to develop through the day as surface heating encourages strengthening onshore flow, coupled with a frontal boundary advancing from the west. If sufficient heating can occur, likely yielding up to 500 J/kg CAPE, heavy showers may begin to develop from early afternoon onwards. Forecast profiles suggest warm air aloft (above 500mb) may limit the height of most convective cloud to around 20,000ft, but this is still sufficiently tall for some lightning strikes. While CAPE of <500 J/kg may appear rather low, this is in part due to it being confined to the lowest ~6km of the troposphere (rather than all the way to the tropopause) and so this in conjunction with PWAT of up to ~33mm will still likely lead to efficient rain producers and the threat of locally large rainfall totals - especially when coupled with generally weak flow through the cloud-bearing layer leading to slow-moving downpours. Showers/storms will tend to pulse up and down, with daughter cells developing nearby on outflow boundaries. The main hazard is local surface water flooding, hence a SVR has been introduced, even if not much lightning occurs. Chances are numerous heavy showers develop, perhaps with limited lightning activity - but a low-end SLGT has been introduced. Showers will slowly weaken in intensity during the mid-late evening, but further outbreaks of showery rain are likely in similar locations through the night hours, exacerbating already wet ground in places.

Elsewhere, a few isolated lightning strikes may be possible from pulses of showery rain moving northeastwards during the morning hours, and with scattered showers that follow into Ireland and western Scotland during the afternoon hours - albeit the risk is rather low in any one location.

[Norfolk Sheep]

12 minutes ago, Jamie M said:

CW Outlook

Day 1 Convective Outlook

VALID 06:00 UTC Sun 19 Sep 2021 - 05:59 UTC Mon 20 Sep 2021

ISSUED 07:49 UTC Sun 19 Sep 2021

ISSUED BY: Dan

The main focus on Sunday will be associated with slow-moving heavy downpours in east/southeast England. Low-level convergence is expected to develop through the day as surface heating encourages strengthening onshore flow, coupled with a frontal boundary advancing from the west. If sufficient heating can occur, likely yielding up to 500 J/kg CAPE, heavy showers may begin to develop from early afternoon onwards. Forecast profiles suggest warm air aloft (above 500mb) may limit the height of most convective cloud to around 20,000ft, but this is still sufficiently tall for some lightning strikes. While CAPE of <500 J/kg may appear rather low, this is in part due to it being confined to the lowest ~6km of the troposphere (rather than all the way to the tropopause) and so this in conjunction with PWAT of up to ~33mm will still likely lead to efficient rain producers and the threat of locally large rainfall totals - especially when coupled with generally weak flow through the cloud-bearing layer leading to slow-moving downpours. Showers/storms will tend to pulse up and down, with daughter cells developing nearby on outflow boundaries. The main hazard is local surface water flooding, hence a SVR has been introduced, even if not much lightning occurs. Chances are numerous heavy showers develop, perhaps with limited lightning activity - but a low-end SLGT has been introduced. Showers will slowly weaken in intensity during the mid-late evening, but further outbreaks of showery rain are likely in similar locations through the night hours, exacerbating already wet ground in places.

Elsewhere, a few isolated lightning strikes may be possible from pulses of showery rain moving northeastwards during the morning hours, and with scattered showers that follow into Ireland and western Scotland during the afternoon hours - albeit the risk is rather low in any one location.

Marginal for me at best. Could really do with 25-30mm. 

[A Face like Thunder]

On 17/09/2021 at 21:57, A Face like Thunder said:

Thank you staplehurst. I meant to say Sunday rather than Saturday for the rain on the NE coast, but I still do not see why such a wide area of England is covered by the yellow warning.

I note that the area covered by the weather warning has been considerable reduced and is now focused on the Eastern side of England. 

[Jamie M]

Sheerness looks to be in for a soaking

[Jamie M]

Quite the structure to that cell in the distance

[Eagle Eye]

Couple cells around, some nice cloud formations 

[Atmogenic]

Was expecting more posts here tbh, but I guess there isn't many members here from East Angelia as when I was out at Folkstone yesterday I saw on the radar the number of cells over East Angelia and thinking they must be having quite an exciting show 

[dr weather]

Some sharp showers just to the east of the IoW currently. Met office is picking up the odd lighting strike (not much).

[Lynxus]

So , convective weather on face book have a severe warning out for a large part of the UK..

 

What coolaid are they drinking or am I missing something today...

Edited September 26, 2021 by Lynxus

[Jamie M]

Day 1 Convective Outlook: Sun 26 Sep 2021

VALID 06:00 UTC Sun 26 Sep 2021 - 05:59 UTC Mon 27 Sep 2021

ISSUED 07:15 UTC Sun 26 Sep 2021

ISSUED BY: Dan

Three main periods of interest exist on Sunday. Firstly, a shortwave trough will nudge from northern France to the southern North Sea, affecting parts of SE England and East Anglia during Sunday daytime. This may provide for the focus for a few scattered elevated showers, but also potentially surface-based given sufficient surface heating through the day. Confidence is rather low as to whether much develops, and so no higher threat levels have been introduced at this stage.

Meanwhile, an active cold front will migrate eastwards across Ireland during Sunday daytime, with a substantial wind shift and thermal gradient. As such, line convection is expected with a brief period of heavy rain and gusty winds. It seems likely this will intensify along the cold front during the evening hours as it crosses the Irish/Celtic Seas, into Wales/SW England from midnight onwards as the Atlantic upper trough becomes increasingly negatively-tilted and PVA increases in the vicinity of the front. Pressure falls will increase across Wales/SW England, and later into the West Midlands, perhaps as much as 5mb per 3 hours with one or more small surface lows forming along the frontal boundary.

These indicators, based on climatology, would suggest a risk of tornadoes (however brief) as a Line Echo Wave Pattern develops, aided/distorted by local orography. Lightning potential is always difficult to judge along squally cold fronts as often the convection is rather shallow in depth with saturated profiles, in an otherwise low CAPE high shear environment. However, there is reason to think a few sporadic strikes may occur, perhaps more especially over SW England and the West Country (Devon / Somerset / Wiltshire / Dorset). Torrential rain and very gusty winds are still likely, whether lightning occurs or not - some guidance flags the potential for 60-70mph gusts offshore and near some coasts of SW England, for example. A SVR is therefore issued for localised damaging wind gusts, and the potential for isolated tornadoes - however it should be stressed that most areas within the SVR may not necessarily experience severe conditions.

 

The final area of interest is the post-frontal environment, as notably cold air aloft associated with approaching upper trough overspreads warm SSTs. Numerous showers will develop over the Atlantic and Celtic Sea, feeding into western Ireland and late in the night into western Scotland, Wales and SW England. Given a few hundred J/kg CAPE and steep mid-level lapse rates, a few sporadic lightning strikes will be possible - especially where showers move inland and are forced over high ground. However, the risk in any one location is too low to justify a SLGT at present.

[Supacell]

2 hours ago, Lynxus said:

So , convective weather on face book have a severe warning out for a large part of the UK..

 

What coolaid are they drinking or am I missing something today...

I think you are probably missing something. CAPE charts show little interest but this is a risk based around other factors as mentioned in the CW forecast.

Later on and tonight a very active cold front/squall line is likely to be pushing eastwards. The risk of thunderstorms is low (hence the LOW threat) but the chance of severe weather is worth noting. There is a risk of convective winds gusting 50-60mph and a possible brief tornado along with a spell of intense rainfall. Not all will see severe weather but some places could get a spell of potentially damaging winds.

[dr weather]

If memory serves, the stated conditions are the commonest (statistically) for UK tornadoes, i.e. instability just ahead of an active cold front.

[Eee]

Just heard some rumbles from this

[emmett garland]

looks torrential at Ipswich

[Dorsetbred]

20 minutes ago, Eee said:

Just heard some rumbles from this

Where the heck did that come from?

[Eee]

No idea. Just popped up out of nowhere.

[Tornadotitan]

Was very strange that storm, could see it from alton resovoir 

[Cheshire Freeze]

Looks like a potentially severe squall line passing through later on tonight/tomorrow morning to me.