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UK/Ireland Thunderstorm Outbreak Thurs May 5th - Wed May 11th

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Author Topic: UK/Ireland Thunderstorm Outbreak Thurs May 5th - Wed May 11th  (Read 381 times)
martinastro
Martin Mc Kenna
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« on: May 04, 2011, 03:02:19 pm »

A very thundery period in store according to GFS and other models for both Ireland and UK from Thurs May 5th to Wed May 11th, or possibly longer, so time to start a thread for posting forecasts and for reports/discussion. High CAPE on a warm unstable Sly or SWly for both locations from late this week, over the weekend and into next week. There will be shear in areas so orgnaised storms with funnel and tornado potential are likely including elevated storms/plumes. Here are the latest words from TORRO's Paul Knightley...

I've been debating whether to start talking about this set-up, as no doubt hopecasting will take centre stage amongst some!  Even so, it looks like warm, humid, unstable air associated with a Spanish Plume, will begin advecting northwards later on Friday. Some thoughts below, although bear in mind that destabilisation is dependant on timing of short-wave troughs, along with, in some instances, daytime heating. Timing differences will no doubt occur, meaning that the thoughts below are not promises!

However, prior to that, some destabilisation of a tropical maritime airmass is likely through the Irish Sea and surrounding coasts into Scotland through Thursday afternoon, evening, and night, which may contain some thunder, in association with a short-wave trough. In addition, showers and thunderstorms may develop across western Eire and western N Ireland on Thursday afternoon.

On Friday afternoon, much of Eire and N Ireland should be in a post cold-frontal airmass. This should destabilise to diurnal heating, with rather strong vertical shear present. Should instability prove sufficient for thunderstorms, organised multicells are likely with a strong wind threat. In addition, low-level veering could be sufficient for low-level mesocyclones/tornadoes.

A short wave may move past SW England and Wales through Friday, with showers and thunderstorms possible with this, perhaps extending into western Scotland overnight.

During Friday night, an elevated mixed layer (EML) originating from the Iberian plateau should spread northwards from France into southern parts of England. There is a reasonable indication amongst models that an area of thunderstorms may develop within this regime, perhaps across Biscay/NW France later on Friday, before moving northwards overnight and into Saturday morning.

How active this is and indeed whether it occurs at all may well be key to the convective evolution on Saturday. A widespread MCS would remove instability from the airmas and quite possibly bring a lot of extra cloud with it - this would limit heating across central, eastern, and north-eastern England on Saturday and hence reduce the thunder risk. If it moves more quickly, or is less widespread, then diurnal heating may trigger some rather intense thunderstorms on Saturday afternoon across parts of the Midlands, and eastern England. Shear profiles look more than sufficient for organised multicell thunderstorms, and are marginally favourable for supercells.

During Saturday night, another area of storms may move north from France across eastern England, before an Atlantic cold front pushes the unstable continental airmass away to the east through Sunday.

This is all, of course, subject to daily changes, and more model information becomes available. In a fairly dynamic convective regime such as this, attempting much detail beyond about 24 hours is very difficult.
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markt
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« Reply #1 on: May 04, 2011, 07:51:13 pm »

Wow!  I do like all this high pressure we've been having, good for solar observing, however I must confess I like 'proper' weather aswell and this synopsis sounds interesting!  Thanks for sharing Martin! Smiley
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martinastro
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« Reply #2 on: May 05, 2011, 01:01:06 am »

Forecast for Thurs...



Storm Forecast
Valid: Thu 05 May 2011 06:00 to Fri 06 May 2011 06:00 UTC
Issued: Wed 04 May 2011 21:54
Forecaster: GATZEN

British Isles

A quite warm and moist air mass advects into the British Isles with southerly low-level winds to the east of an Atlantic low pressure system. Latest Valentia sounding indicates nearly neutral lapse rates that will easily allow for weak CAPE due to daytime heating. Latest model output indicates weak instability over the southern and western British Isles on Thursday afternoon. Sea breeze convergences are forecast to assist initiation that will become more likely near a mid-level jet streak pointing towards Ireland. The severe threat is forecast to increase in the western parts where rather strong south-westerly winds are expected. Especially in the evening hours models suggest increasing low-level vertical wind shear (SRH 100 mē/sē in the lowest kilometre) that will overlap with some weak CAPE. This may support tornadoes, and some events are not ruled out. Limiting factor will be the rather weak low-level convergence, and a level 1 threat is not forecast. Storms are expected to weaken after sunset.
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« Reply #3 on: May 05, 2011, 05:26:08 am »

Hmm, better take my brolly to work today then.  Thanks Martin...
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« Reply #4 on: May 05, 2011, 07:53:18 am »

Quote
better take my brolly to work today
Hmmm, I bought a new brolly about 6 weeks ago, it hasn't rained since until this morning. Probably a good idea to buy another.
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martinastro
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« Reply #5 on: May 05, 2011, 10:25:05 am »

Updated forecast from Tony Gilbert....



A low risk Outlook

Slight Risk of an Isolated Thunderstorm Ireland, Wales, central and northern Regions UK 12Z-21Z

Prime Risk Hail & CG's/ Marginal Risk of Tornado Event as per red boxes

Low pressure central Atlantic maintains SWerly Polar Maritime flow across UK & Ireland.

Cold front over Ireland expected to initiate isolated convective showers by afternoon some of which may become thundery. Surface trough expected to develop over western UK through today with isolated convective showers initiating primarily Wales through to northern UK regions by late in the day.

Some specific attention is given to region noted by red boxes on convective map below. Low level helicity values increase during the afternoon and move into the realm of tornado genesis by way of shear. Not much increase above this level in vertical shear with height until above 500mb where a stronger jet lays beneath the tropapause. Cloud tops have the potential to reach 250mb today with cooling to a -55 deg C (Very cold tops) The combination of low lifted condensation level and low level of free convection with a moist 95 % humidity at surface could see towers reaching the full height. End result could see some slight upper support adding longevity to any stronger building cell. A very dry intrusion at 500mb is now shown by GFS and will increase potential instability to developing storm cells by late in the day. It is these combination of features which give the chance for stronger cell development and so too for tornado genesis.

There are many influencing factors for the above not excluding ristricted PVA and only weak upper troughing. So the overall risk would appear to sit on the fence and could just as easily go either way. Any Sferic activity likely to be fairly restricted right across the board.
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martinastro
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« Reply #6 on: May 05, 2011, 06:33:06 pm »

Convective update from Paul Knightley...

At the moment, a warm and moist airmass is spreading northwards, although surface air is still fairly dry, especially in the east. Showers and longer spells of rain are present in the west, associated with the... cold front along with an upper trough, which is moving through N Ireland – Wales towards N England and Scotland. Thunderstorms could develop across N England in the next few hours, associated with this and some diurnal heating.

Tonight, another short-wave trough will move into southern Ireland, also passing through western parts of Britain and through the Irish Sea, into Scotland by morning. There is a chance of thunder with this around the Irish Sea coasts after midnight and into S Scotland later on tonight. However, the lapse rates are not that steep as the airmass is still maritime in origin so it might be a struggle to get anything going thunder-wise.

This trough will move away on Friday morning such that a fairly flat upper south-westerly flow will be in place. Widespread lift is not indicated, so although a few showers are likely in the west, widespread activity looks unlikely – Wales perhaps has the best chance of thunder through the middle of the day into the afternoon.

Later tomorrow, the large trough to the west of Europe will tend to dig towards Iberia a bit more. The southerly flow will strengthen at all levels, and strong warm air advection will commence. This warm, moist air will be topped by an elevated mix layer from Iberia, increasing instability. It looks like the warm front on the nose of this airmass will move into south-western areas of England tomorrow afternoon, and then lift northwards (probably most quickly in the west) through tomorrow night into Saturday morning. Showers and thunderstorms are likely to accompany this, but the detail is still hard to pin down.

Most likely, several thunderstorms will form over France, or in Biscay, on the nose of the warm advection, and move into southern and south-western parts of England and Wales through the evening and overnight. Model variations preclude knowing where the most active storms will be, but I would think SW England, parts of Cent S England, and Wales/W Mids are most in line, before moving into S Scotland after midnight – this may be in the form of an MCS. However, other storms may well drift into SE England through the night, and thence through the E Mids.

Saturday is a complex day, and better dealt with tomorrow – however, the thundery plume will have engulfed much of Britain – thus showers and thunderstorms could occur almost anywhere. The most likely location for surface based storms in the afternoon is from the N Mids northwards into SE Scotland. Shear looks sufficient for well-organised thunderstorms, including supercells, with large hail, damaging winds, and tornadoes possible.

Other storms may move into S England through the day from France, and an upscale growth of activity into one or more MCSs is possible through the evening and first part of the night, as the main part of the trough starts to swing in.
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« Reply #7 on: May 05, 2011, 06:46:13 pm »

Hmm, better take my brolly to work today then.  Thanks Martin...

Well, I took a jacket in the end, but good job I did as was raining come home time...

The update sounds exciting! Smiley
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martinastro
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« Reply #8 on: May 06, 2011, 01:23:06 am »

Forecast for Fri from Netweather.tv - risk of possible severe storms and tornadoes....



Valid: 06/05/2011 06:00 - 08/05/2011 06:00
Headline: ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FORECAST...

Synopsis
This forecast will cover the period Fri/6th 06z to Sun/8th 06z. A large low pressure system within a deep long wave trough will be anchored to the west of the British Isles throughout the forecast period. A strengthening southerly jet stream on the Ern flank of this trough will shift slowly east during Fri and Sat, while at the surface a slow-moving waving cold front across the west both days will finally shift east across UK Sun AM. Warm moist southerly flow ahead of this cold front will become increasingly unstable with thunderstorms expected to develop in places over next few days.

... FRIDAY DAY - EIRE, WALES, N MIDLANDS and N ENGLAND …

Increasingly moist southerly flow across the UK and falling heights/pressure from the W will see instability increase from the west during the day. Models indicated SBCAPE values of several 100 j/kg across Wales, N Midlands and N England in the afternoon - so insolation and nearby cold front will likely trigger scattered heavy showers and a few thunderstorms by evening. 30-40 knots of deep layer shear as southerly flow increases aloft and with winds backed SE at surface - we may see any storm organise with a strong wind gust threat along with hail and perhaps a small risk of an isolated tornado. A greater severe threat exists across Ireland/N Ireland in post frontal rPm airmass, where colder uppers generate greater instability combined with stronger upper winds - which suggests a slight risk of a severe storm possible, namely moderate hail, strong wind gusts and with strong low-level shear and dry mid-level intrusion indicated - a risk of a tornado.

... FRIDAY NIGHT - WALES and CENTRAL / SERN ENGLAND ...

A plume of higher dew points /theta-w values is forecast to advect NNE from W France/Biscay late Friday ... an upper shortwave trough is indicated to move NE and destabilise the plume across NW France and later across S/C England and Wales which will develop an area of thundery rain with embedded mainly elevated thunderstorms overnight into Saturday morning before clearing E Anglia/E England by 12z. Strengthening Serly upper winds and some moderate vertical shear may organise storms into a MCS ... with a risk of hail, gusty winds and localised flooding.

... SAT/7TH - EIRE, ENGLAND, WALES AND S/W SCOTLAND ...

Much of mainland UK will still be beneath a warm/moist southerly flow ... after overnight rain/storms clear, insolation is indicated to develop several 100 j/kg CAPE across Wales, central and N England and parts of Scotland. So afternoon thunderstorms are likely to develop in these areas, with a pre-frontal trough indicated to move NE which will enhance forced ascent of warm/humid airmass. With a 100mph+ jet at 300 mb indicated towards Wales/W England and 30-40 knts DL shear - organisation of storms into multicell line segments is likely and perhaps one or two supecells can't be ruled out - with strong low-level shear also indicated giving an enhanced risk of one or two tornadoes if storms become surface-based. Also, there is risk of moderate-large hail and strong convective wind gusts. A few t-storms are also possible across Eire in the afternoon in rPm airmass, with risk of hail and gusty winds and maybe an isolated tornado. Cold front in the west over E Ireland on Sat will then move east over UK overnight and through Sunday AM, bringing heavy rain with embedded mainly elevated thunderstorms in places with risk of hail and gusty winds.
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« Reply #9 on: May 06, 2011, 01:48:49 am »

looking good!!!!!
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JohnC
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« Reply #10 on: May 06, 2011, 08:18:01 pm »

It's 2012 and we have a half-decent TS coming out of the SW and there's quite a bit of it  looking at Raintoday, it's come up from NW  France and moving NE through Cornwall and Devon. A lot of lightning showing  (Blitzortung) in cells moving into the English Channel.

Just modified  -  after 2 minutes now lightning and heavy thunder.
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martinastro
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« Reply #11 on: May 06, 2011, 09:43:20 pm »

The ATD sferics charts look awesome John!!  Smiley
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martinastro
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« Reply #12 on: May 07, 2011, 01:09:01 am »

Outlook for Sat from Paul Blight...



The whole of England and wales and parts of S Scotland is at risk of Showers and Thunderstorms on Saturday, but it can be split into two main areas.

Zone 1 - Northern England, Southern Scotland. Best risk here of Surface based convection developing during the day esp where orapgraphic enhancement will aid the process (Pennines, Peaks moors and fells for example) Strengthening and 300/500mb flow caused by the Sharpening trough will tend to increase the risk of organised convection developing with organisation of cells into multi cluster cells or possible MCS with time esp as the evening progresses. Large Precipt Water content of forecast ascents here indicates potential for local flooding in localised spots 20-30mm and risk of hail if cells can tap into the colder air aloft.

Zone 2 - Southern Half of England - Risk of overnight showers and storms dying out slowly- a lot of Medium level cloud but some sunny spells developing, will allow insolation to increase temps, convection will be initiated but BLRC will depend on insolation, at the same time, a shortwave to the west of Iberia will sharpen and swing North over SPain and France before arriving across S England tomorrow evening. This Shortwave will back the flow aloft and strengthen it - at the same time as destablising the underlying high WBPT plume at 850mb which has now arrived having left the SPanish Plateau some days ago. This shortwave will help to destabilse the EML and also aid any convection which has routed inthe BL. Temps of 22-24C (up to 26C in London) will prompt heavy downpours to develop - primarily towards the Late afternoon and evening. A mix of elevated and surface based convection seems possible here with any surface convection largely inland and north of the M4 and NW of London. London and the SE and East Anglia largely seeing a drier airmass and chances of convection limted here, though Lincs likely exempt from this zone.
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martinastro
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« Reply #13 on: May 09, 2011, 12:10:01 am »

Storm forecast for Monday from Tony Gilbert...



Moderate risk of isolated thunderstorms Ireland, Wales, northern UK & Scotland 09Z-21Z

Quasi stationary filling low west of the UK continues to feed unstable northward across the UK. Deep upper troughing increases lapse rates rapidly by early on in the day. With some minor insolation we can expect to see some sharp convection initiate and spread north. With a very cold pool aloft we should see numerous cumulonimbus formation with classic anvil at the tropapuse. Elevated strong jet stream will slide the anvils off to the NE. Some moderate increase in vertical shear with surface troughing aligning with streamlining vector will develop line convection in train motion. Credit: Tony Gilbert from UKWW.
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« Reply #14 on: May 09, 2011, 06:49:47 am »

Excellent update there thanks Martin!  Already looking ropey here in the west mids and it's not 7am yet.  Another day for the coat and brolly me thinks...
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