Convective/Storm Discussion

[Neilsouth]

The rain is really coming down it's torrential... Funny we got more rain now than we did the other day with that low pressure system.

[Coast]

Cant see anything thunderstormy associated with the low coming in tomorrow although their might be a lot of rain (see dedicated thread) but Wednesday and next weekend starting to look like they have some of the right ingredients:

Although Wednesdays seems to start breaking down as it approaches Ireland:

With a lot more going on at the end of the month into November perhaps?

Watching and waiting.....

[Jane Louise]

I have just read tonight from different sources that there maybe isolated thunderstorms from Tuesday toThursday!! Met Office have even mentioned possible hail and thunder for the South West on Wednesday.

[Coast]

Oh well, here goes then with the first of the other severe weather sites proposing a little something off Southern Ireland and Cornwall for today:

Storm Forecast

Valid: Tue 20 Oct 2009 06:00 to Wed 21 Oct 2009 06:00 UTC

Issued: Tue 20 Oct 2009 03:57

Forecaster: VAN DER VELDE

SYNOPSIS

The cold front of a very large low pressure system, situated between Greenland and Morocco with its center west of Ireland, reaches the Iberian Peninsula and western France. On both sides of the front destabilization takes place. Predicted EL temperatures are initially not so cold over land (-10°C) which could inhibit thunder, but chances are better in the south and east where more moisture is advected onshore.

Another upper low centered over Hungary affects the area around the Black Sea, with northward advection of a warm sector unstable airmass into Moldova and Ukraine.

Very messy again today, so no disappointed faces if this all comes to nothing eh?

Maybe tomorrow onwards if that front can get moving?

[Harry]

Southern Portugal and SE Spain seems to be hogging all the glory again - lucky so and so's.

I have had dreams the last couple of nights of thunderstorms - either a result of an ever growing craving, or I am officially a Seer!

The FAX chart seems to indicate a kind of LP magnet, or LP velcro somewhere off the coast of SW Ireland - each LP centre that seems to arrive there seems to get stuck and can't escape, lol

Edited October 20, 2009 by Harry

[Nick F]

Have issued a storm forecast for SW England, S + W Wales, Irish Sea, S + W Ireland for tomorrow as lapse rates steepen and maritme airmass becomes unstable from the west over these coastal areas behind the occlusion moving east tonight/morning:

http://www.netweather.tv/index.cgi?action=convective;sess=

Looks like a repeat for these areas and maybe further east on Thursday too.

[Coast]

ESTOFEX still have it off the coast of Cornwall today:

Storm Forecast

Valid: Wed 21 Oct 2009 06:00 to Thu 22 Oct 2009 06:00 UTC

Issued: Tue 20 Oct 2009 21:38

Forecaster: PUCIK

A level 1 was issued for Portugal mainly for severe wind gusts and tornadoes.

A level 1 was issued for Southern coasts of France and Northwestern Italy mainly for excessive rainfall and to the lesser extent for tornadoes.

A level 1 was issued for Western Italy mainly for tornadoes and to the lesser extent for severe wind gusts.

SYNOPSIS

A deep mid-level trough over the eastern Atlantic will be a major factor in the weather development during the day. Its southern part will move quickly to the east with strong jet surrounding it. Jet-streak with speeds over 70 m/s at 300 hPa embedded in the northwesterly flow should result in the strong synoptic impulse, travelling across Portugal and Spain in the evening hours. A cut-off low situated over the Central Europe should progress to the northeast, slowly filling.

At the surface, two main pressure systems will dominate - a high over Russia and a large low centered just west of Ireland coast. This low has occluded and filled with moist maritime polar airmass so that widespread bands of showers or weak thunderstorms are anticipated in the environment of weak shear and marginal instability. Strong cold front will cross the Western Mediterranean during the day and will affect Italy in the late evening and night hours. The aforementioned developing impulse will result in cyclogenesis and another frontal system will cross Iberian Penninsula.

DISCUSSION

... Southern coast of France to Northwestern and Western Italy...

As the cold front progresses eastward, a plume of high Theta-E values will spread northwards, ahead of the significant frontal trough. Also, high lapse-rate airmass with origin from Northern Africa, overlying the warm and moist airmass over the Mediterranean. This combination will yield a tongue of instability with MLCAPE values around 1000 J/kg, with the highest values around the western coast of Italy towards the late evening and night hours.

Low level jet is expected to form ahead of the front, with windspeeds between 20-25 m/s at 925 and 850 hPa level and this feature will have a delta mostly over the southern coast of Spain and northwester coast of Italy. At mid-levels, strong flow around the trough will yield moderate to high values of DLS, between 15 and 25 m/s. Ageostrophic flow induced by the pressure falls ahead of the trough and strong winds at lower levels should result in very high SREH values, in 0-3 km models generate locally more than 400 J/kg. Low level shear will be strong as well, its values reaching more than 15 m/s. Such environment is conducive to well organised, rotating thunderstorms.

One of the detrimental factors should be the lack of synoptic-scale forcing and thunderstorms will mostly initiate around the front or close to the coasts, where southerly flow will impinge on the land. With high moisture content and a possible "thunderstorm training", excessive rainfall is possible, especially concerning the southern coast of France and northwestern coast of Italy. Low LCLs, high SREH values in 0-1 km and strong LLS well above 10 m/s point to the threat of tornadoes, especially in the case should the unstable parcels stay rooted in the boundary layer. The tornado threat depends on the fact, whether the instability, confined mostly to the coastal areas, will overlap with strong shear, but at this time models simulate the overalp (mainly over western coast of Italy), so this risk is included as well. Around the western coast of Italy, marginally severe gusts might occur as well, due to the strong flow at 850 level ( 20 m/s) with strong component perpendicular to the boundary and quite high lapse rates over the region.

A high end Level 1 is issued and an update might become later on, when the overall threat proves to be higher than previously anticipated.

I guess it all depends on when and where the front moves through:

I'll wait until later to see what tomorrow might bring, as the charts don't currently show any potential moving East enough to my location, although Devon and Dorset might get lucky!

[Harry]

Even this relatively unsettled spell is looking naff - almost as if we are now being influenced by an area of 'Lower High Pressure' than HP. Calm outside, if a little cloudy and damp.

Had another dream about storms last night - think the craving is really cranking up now, lol

[Coast]

Had another dream about storms last night

Harry, you need to stop eating cheese before you go to bed

[Harry]

Harry, you need to stop eating cheese before you go to bed :unsure:

I've not consumed cheese, at all, for the last three weeks (dieting, lol). Fruit tends to have a similar effect so should probably give that up close to bedtime too

[Harry]

Subtle observation - MetO forecasting the potential for heavy showers moving across southern and southeastern England evening and overnight tomorrow, with respectable CAPE/LIs for the time of year, and a storm risk around 30-50%.

Might be worth keeping an eye on, though I do expect the charts to read differently this time tomorrow (as is sods law)

Edited October 21, 2009 by Harry

[NL]

NW lightning detection has picked up several Sferics through the English channel moving NNE towards Exeter.

[Evening thunder]

Just had a pretty good soaking from that line of showers now just to the east of Exeter! Torrential at times and has deposited 7.4mm so far in about the last half an hour id guess but still raining as were just catching the edge of the line now.. cant look at full stats though as normal pc is playing up so can just look at weather station screen.

[SteveB]

The BBC has storms for the South West from as early as 3-4am tomorrow morning, becoming heavier and more wide spread as the day continues.

[chapmanslade]

Don't think storms will initiate at that time, nor will they be widespread. Should any storms develop tomorrow they will do so in the region of best CAPE, which according to GFS and the NMM model will be over the SW. Perhaps a few scattered showers becoming more widespread during tomorrow but storms should be confined to the SW, and also Sern parts of Wales.

They are already there - don't forget the sea is at its warmest so they will develop at sea and then push inland - fizzling as they do at night.

[DAVID SNOW]

Thursday into friday for the south could be interesting

[Nick F]

Have issued a storm forecast for Thursday, perhaps chance of a storm further east later tomorrow for coastal S England and also further north over coastal Ireland and perhaps W coasts of Scotland:

http://www.netweather.tv/index.cgi?action=convective;sess=

[Coast]

I see Carol was airing her humdingers on the BBC this morning! :lol:

UKASF and TORRO have not put up any storm forecast for today but ESTOFEX have a big one and very interesting if you live in the Mediterranean and Italy in particular. Western parts of the UK are highlighted however:

Storm Forecast

Valid: Thu 22 Oct 2009 06:00 to Fri 23 Oct 2009 06:00 UTC

Issued: Wed 21 Oct 2009 23:52

Forecaster: TUSCHY

A level 2 was issued for parts of the western Mediterranean, the Tyrrhenian Sea, W/SW Italy and parts of Sicily mainly for excessive rain, tornadoes, severe wind gusts and large hail.

A level 2 was issued for parts of the E/NE coast of the Adriatic Sea mainly for excessive rainfall.

A level 1 was issued for the surrounding areas, including the western and the central Mediterranean.

SYNOPSIS

A highly negative tilted trough affects western and central Europe and induces a strong surface depression over the western Mediterranean. Another impulse further northeast affects the central Mediterranean with unsettled conditions. The rest of Europe remains cool and stable.

DISCUSSION

... Bay of Biscay and northwards ...

A weak shear/moderate CAPE environment evolves in that area beneath eastward propagating, cold mid/upper trough. Scattered showers/thunderstorms are forecast with decreasing trend in coverage and intensity later the day. Strong wind gusts and marginal hail are the main risk.

Here are some charts and models to help make your own mind up!

London forecast for 1800 hrs:

Plymouth:

[Jane Louise]

Thanks for the update Coast. Maybe one may drift my way today lol.

[Coast]

Thanks for the update Coast. Maybe one may drift my way today lol.

More likely you than me I think!! :lol:

[SteveB]

Meto have warnings out for my area regarding heavy showers.

Frequent heavy showers are likely to produce accumulations of 15 to 20mm within 3 hours at some locations giving rise to large amounts of surface water.

The public are advised to take extra care and refer to the Highways Agency for further advice on traffic disruption on motorways and trunk roads.

Issued at: 1049 Thu 22 Oct

[A.J]

Some pretty hefty radar returns for parts of wales and the SW Midlands, as an organized area of heavy rain pushes Northwards, not electrical in nature at the moment, but wouldnt be surprised to see on here a few reports of flashes and rumbles this afternoon....looks like quite a soaking heading my way over the next few hours

[Costa Del Fal]

Pretty heavy shower passed through here. Almost like you would get in the summer really.

[TonyH]

My wife heard 2 rumbles thunder an hour ago.

Torrential showers 8mm past hour.

[A.J]

yes, as posted earlier, a summery look to the evening skies, with some beautiful Cb cloud vistas to my east, and a big mature anvil way off to my west