Conv/Storm Discussion 31/5 & Early June

[VillagePlank]

Looks promising for Friday night, now.

LI is very low (-6 = severe thunderstorms possible), CAPE is very high (1024=lots of convection possible), K Index is reasonable (25=Isolation Thunderstorms), and TT is good (53=numerous thunderstorms, scattered tornadoes)

Convective temperature is about 19C which is what GFS is predicting for the minimum 2m temp for late afternoon. DP's are reasonably high with high RH levels in and around the channel (>85%) for most of the afternoon - although this does migrate east, a little.

Chances, with 60 hours to go? I'd say 50% for London, but expect downgrades closer to the time. CAPE is almost always overcooked this far out.

Interesting enough to keep an eye on the relevant charts for Friday afternoon, though.

EDIT: and no CIN!! - and changed probability to 60%

Edited June 6, 2007 by VillagePlank

[Supacell]

And (as per usual) the 12z has seriously downgraded thunderstorm potential for Friday!

[Nick F]

Tomorrow, upper low/vortex over Scotland is likely to create lift of increasing sfc moisture, upper cold pool associated with upper low will help steepen lapse rates too -

-300hPa relative vorticity and 500hPa heights and temps.

... so a chance of heavy showers with thunder developing, Highlands and Southern Uplands look favoured with help of orographic lift:

Friday

Elevated moist plume of increasing Theta-w (WBPT) values upto 16C looks to advect across SE England overnight Thursday into Friday morning, although GFS CAPE charts don't reveal much in the way of CAPE and fcst skew-ts show a cap, elevated moist layers aloft are modelled to become increasingly unstable through differential thermal advection or in laymens terms increasingly colder air arriving above elevated moist layer making it unstable. Heavy thundery rain from mid-level cloud with possible elevated storms are modelled by GFS to move across Kent and Essex friday morning.

Friday 00-06z 700hPa Theta-w values:

Kent fcst skew-t for 06z Friday:

Some uncertainty with modelling thundery preciptiation likely to move up off the near continent on Friday, 12z GFS has precip. Friday morning moving North across Kent and Essex, 12z UKMO dry in the morning but later through the afternoon and on overnight into Saturday has an MCS moving North across SE and E. Anglia.

[Supacell]

Got up this morning to find that BBC forecasts are now putting out thunderstorms in eastern areas tonight into tomorrow. Looks very much like an MCS system moving up from the near continent. Rainfall rates look to be very high and BBC forecast mentioned up to 2 inches of rain likely!!!

GFS support this but show very little CAPE. Nick you mention elevated storms over mid level clouds, does this mean any lightning will be hidden or are these the type of storms that produce good lightning displays?

Edited June 7, 2007 by Supacell

[Supacell]

GFS support this but show very little CAPE. Nick you mention elevated storms over mid level clouds, does this mean any lightning will be hidden or are these the type of storms that produce good lightning displays?

Have just found some information which answers part of my question. Thought it was interesting and will help those, like myself, that tend to rely very heavily on the CAPE and LI index to check for storm likelihood.

"It's important to remember that those CAPE/Lifted Index charts need to be interpreted with caution with respect to elevated storms, as they depict values closer to the surface - and can thus miss significant CAPE/instability aloft!"

Still need to ask if these elevated storms are any good for lightning though :lol:

[Nick F]

"It's important to remember that those CAPE/Lifted Index charts need to be interpreted with caution with respect to elevated storms, as they depict values closer to the surface - and can thus miss significant CAPE/instability aloft!"

Still need to ask if these elevated storms are any good for lightning though :lol:

Like you say, CAPE charts don't always reveal mid-level instability, though atm the rain forecast to spread North across East Kent and Eern East Anglia isn't suggested to be particularly electrically active, more thundery downpours than anything else. Mid-level storms are usually good for intra-cloud or cloud-to-cloud lightning, and can be quite prolific in this respect at night time when cloud tops cool.

Chance of some heavy showers with hail and thunder over the Highlands this afternoon as mentioned in my earlier post yesterday evening.

Tomorrow morning in early hours an elevated moist plume of high theta-w (wet bulb potential temp) values advects North across the SE and East Anglia - this plume unstable in the mid-levels through differential thermal advection (cold pool aloft steepening lapse rates) and trough creating lift:

... still a little uncertainty to how far West the possible thundery rain will get as it moves North, UKMO the heaviest rain moving North across Kent, East Essex/Suffolk/Norfolk, GFS a little further East:

UKMO:

GFS:

Kent Forecast skew-t reveals elevated moist plume aloft, though little instability, fairly high precipitable water shown towards North Sea - so potential for heavy downpours:

[kold weather]

Yeah I'd say thundery rain looks more of a possiblity IF it comes off at all wit hthe cells that are currently forming over France pushing up from France overnight and strengthening as positive voricity also increases. As you say Nick cape isn't everything, though there is hardly none present on the GFS run our side of things.

Looking at things at the moment i think its really 50-50 as to whether the cells get far enough west to give really heavy rain to the SE/East Anglia, the axis line right now suggests to me the heaviest of the rain will remain off-shore like the GFS but still time for that to change. Both models though are forecasting quite a lot of rain could fall though with this system, not sure how much because it'll depend on how well the cells survive as they come up from France hnowever as Nick has said there is a lot of precipitable water shown and so shouldn't take too much for heavy rain to develop on this disturbance.

Going to be one of those wait and watch set-ups!

[Arrows]

Well finally I might see a storm or two. It looks very heavy on the GFS, Is this realistic as the GFS under or overplays systems. Is this more of a wet system with embedded storms?

[johnholmes]

its still about 50:50 as to whether the area of rain, largely unstable medium cloud, gets far enough west for it to affect the se and e anglia.

its being monitored all the time and we will update you later this afternoon.

[Arrows]

^Thanks John

[Joneseye]

Latest radar shot from europe shows some cells breaking out in France and quite a large cell to the SW of Paris..

[RisingStar]

Latest radar shot from europe shows some cells breaking out in France and quite a large cell to the SW of Paris..

Looks like the cluster of cells over to the east of France will be the area too watch this afternoon. Temps are around 25/26c where the storms are, the north looks abit fresher, only 20c in Paris.

[Joneseye]

Looks like the cluster of cells over to the east of France will be the area too watch this afternoon. Temps are around 25/26c where the storms are, the north looks abit fresher, only 20c in Paris.

Good shout! Since I last posted they have really sprung into life:

From my own observations this is nothing new, but certainly with the forecast for storms to move up overnight it is definitely worth keeping an eye on..

Latest from http://www.estofex.org/

Nothing too severe forecast:

Storm Forecast

Valid: Thu 07 Jun 2007 06:00 to Fri 08 Jun 2007 06:00 UTC

Issued: Wed 06 Jun 2007 21:55

Forecaster: GATZEN

SYNOPSIS

Weather situation did not change significantly. High over Scandinavia remains, while several weak upper cut-offs are situated over northwestern Europe. Low geopotential centered over northern Mediterranean has weakend compared to WED. Strong westerly jet at the southern flank of this upper low remains.

DISCUSSION

Benelux

A surface low is expected to develop over France/southwestern Germany during the day, providing warm air advection over Benelux. Given steep mid-level lapse rates and rather rich moisture in low-levels, instability will likely realize. However, do not see that dewpoints will reach around 20°C as indicated by latest GFS model run. Additionally, low-level air mass may be relatively cool. Expect that thunderstorms will form during the afternoon/evening hours that may be elevated over some places. Given increasing north-easterly surface winds and therefore increasing vertical wind shear, chance for organized convection will be increased, too. A few multicells are forecast to develop, while only low chance for large hail is expected. Thunderstorms may go on well into the night in the warm air advection regime.

Northern/central Italy, Alpine region and southern/western Germany into France, northern Spain, Czech Republic and Poland

Boundary-layer moisture has improved over France as indicated by latest soundings, and quite steep lapse rates especially below 600 hPa are also present. This will result in CAPE during the day due to diurnal heating. Weak CIN is present, and convective initiation is expected in the range of low-level convergence zones/outflow boundaries of old convection or upslope flow regimes in hilly terrain. Quite strong buoyancy at relatively low levels will likely result in strong updrafts initially, while weak vertical wind shear is expected to inhibit organized convection over most places. Isolated large hail can not be ruled out with convective cells in the early mature stage. North and west of this area with rich low-level moisture, latest soundings indicate inverted-v-profiles and at least weak instability. Thunderstorms are expected to develop during the day, while a few strong downbursts are forecast to be the main threat. Intense precipitation and local flash flooding is forecast to be a significant threat over a broad area.

[kentish_sally]

Hello everyone! This is the first time i have took the courage to post, But the surface low - Does that mean for the storm potential to grow within the SE and E Anglian regions the low would have to be situated off of the south / kent coast to get a more SE'ly wind direction to blow any storms further in land?

Also where is the system positioned in actuality?

[Supacell]

Looks like there is quite a bit of electrical activity in those cells just now attacking the east coast. Areas such as Durham, Northumberland and up into SE Scotland.

Proof that CAPE is not always necessary for thunderstorms.

Hopefully the same thing will occur tomorrow morning for the SE. Incidentally the East Mids radio forecast mentioned these storms could affect this area tomorrow evening. These cells are forecasted by the met office to move in a NNW'ly direction tomorrow and thus areas such as Lincolnshire could also be at risk later Friday evening.

Edited June 7, 2007 by Supacell

[VillagePlank]

Hi Sally

If the pressure is low then it enables the atmosphere to become unstable. An unstable atmosphere enables bouyancy which means that parcels of air can rise. If they can rise they can form clouds. Depending on the state of the atmopshere (the stuff that we all jabber on about in this thread) depends on how big the clouds get; if they get big enough t/storms can form.

I think that's right! Keep on posting! Welcome to net-weather, too.

Which part of N Kent are you from?

Edited June 7, 2007 by VillagePlank

[Andy Bown]

It's a similar worded set up (as posted by Nick above) to the 30th April/1st May 2005 night-time spectacular that moved up from the SW, across the Bristol/Wiltshire/Gloucestershire area and into the Midlands. There wasn't widespread precipitation, but what there was was torrential inc. hail, however there was almost constant lightning visible for a number of hours.

I hope for you storm lovers in the SE/E that similar happens tonight!

[kentish_sally]

Hello and thank you for the welcome village.

I understand the Lifted Index (the parcel of air) and CAPE values required for storm initiation, I was more thinking in an idealist situation that the CAPE and also L.I was ideal within the possible events tonight moving up from France (and hopefully forming Kent's first imports i belive) what would it take for the precipitation and / or storms to be dragged into the South East?

The only thing i could see is winds from the SE or ESE'ly direction from that of the surface low blowing them (trough perhaps?) into the forementioned regions But is this likely?

Im also two train stations north of you, The quaint and quiet side of Higham

[Stuart]

and the storm is only 55km from me

[franswali]

It's a similar worded set up (as posted by Nick above) to the 30th April/1st May 2005 night-time spectacular that moved up from the SW, across the Bristol/Wiltshire/Gloucestershire area and into the Midlands. There wasn't widespread precipitation, but what there was was torrential inc. hail, however there was almost constant lightning visible for a number of hours.

I hope for you storm lovers in the SE/E that similar happens tonight!

I remember that night, it was the night before I got married, couldn't sleep anyway so it was a welcome distraction

[Stuart]

all the storms need to do is move a bit more to the west

Edit 47km from my area and it moveing at 44 kPS

Edited June 7, 2007 by Stuart H

[BrickFielder]

Midday soundings are in from across the continent and its a mixed bag really. It is not as moist as GFS forceasted across France at upper levels but GFS seems to have been pretty good at where precipitation will break out.

06Z suggests wind convergence at 500hPa across the channel tonight into tomorrow will converge moisture and send air exploding upwards. Impressive 500hPa vertical velocities are forecast.

Low level conditions are not really condusive to storms so I think we are looking more at elevated storms off or just over the south east coasts. Some lightning and perhaps some isolated hail ,and I am not sure how much rain will reach ground level.

Surface low over France will be advecting (moving) moist warm air from there north towards us at mid to upper levels, whilst in contrast at low levels winds will be coming from the north.Typically higher based storms produce some spectacular lightning displays ,but low level winds are still likely to blow in some low level mist and clouds perhaps obscuring the view.

Elsewhere a few storms are blowing in from the east into northern England and Scotland.

More chances of storms tomorrow and into the weekend.

[Michael Winston]

Midday soundings are in from across the continent and its a mixed bag really. It is not as moist as GFS forceasted across France at upper levels but GFS seems to have been pretty good at where precipitation will break out.

06Z suggests wind convergence at 500hPa across the channel tonight into tomorrow will converge moisture and send air exploding upwards. Impressive 500hPa vertical velocities are forecast.

More chances of storms tomorrow and into the weekend.

Some promise for us Midlanders, then, Brick?

Kind regards,

Mike.

P.S. That second chart looks like the Olympics logo!

[Stuart]

storm look like it going to miss my area

[johnholmes]

I'm not sure it was ever predicted to affect your area Stuart.