Storm Risk Discussion

[Coast]

Lol, rumbles float my boat at the moment because I am so starved its ridiculous! The quietness of it all is so depressing, along with the fact every event so far has either missed me, or been completely dank!

Those of a storm starved disposition may want to look away from this link (or move to central France or NE Spain!) currently: http://rfham.free.fr

Ties in perfectly with the ESTOFEX forecast for Europe today.

Nothing reported for yesterday for funnels or Tornado's in the UK, but it was quite active in Holland and Germany yesterday: www.essl.org/ESWD

[Harry]

Two confirmed funnels/tornado from the weekend then

Might not be much 'severe' weather around in terms of severe storms, but we are starting to live up to our record of most tornadoes per sq mile

Seriously though, look at that rain band over the last two hours - it moves up, fragments and completely tears in two to miss most of the UK - and people laugh at the term 'shield' lol

Nothing reported for yesterday for funnels or Tornado's in the UK, but it was quite active in Holland and Germany yesterday: www.essl.org/ESWD

According to that, there were tornadoes, funnel clouds, severe wind gusts, large hailstones, but no where saw heavy rain B)

Edited June 8, 2009 by Harry

[VillagePlank]

Those of a storm starved disposition may want to look away from this link (or move to central France or NE Spain!) currently: http://rfham.free.fr

A chance to introduce a basic convective parameter Dewpoint Depressions, Tdd

Consider this actual skew-t from the 12z sounding

The horrible black lines are mine to indicate large Tdd. Tdd is the difference between Tc, and Td (temperature and dewpoint, respectively) at any specifc pressure.

What this means in 'real' terms is that if the bit beneath the high Tdd is bouyant (it is because, kindly, the producers of this chart have drawn our parcel trajectory in grey, and nearly the whole sounding is bouyant - we haven't reached equilibrium to nearly 350hPa) then a large difference between Tc, and Td, means the air is dryer. If Tc=Td then there is 100% humidity.

How is this useful? Well, apart from some use to determine cloud base, if the lower levels are bouyant, the mid levels have a high Tdd, then this acts rather like a nitrous-oxide turbo fitted to a car - it gives the air packet a bit more lift for a little while (evaporative cooling increases) ..... here you have four good 'punches' to keep that air packet lifting.

It is not useful to predict severe weather, but, if severe weather initiates, it can be useful to determine exactly how severe it might get. Here, you have Tdd's of >10C at 750hPa and 400hPa, if convection has initiated at the surface and those air packets can get to those heights, then such an air packet will get a bit of kick to keep going. A high Tdd at mid-levels is also useful for deciding if hail will fall, too.

Hope that makes sense? What you need to look out for is an unstable surface (look at the right panel, and it will tell you the most unstable area) and a high Tdd between 850hPa and 500hPa (mainly) for that extra kick

EDIT: whoops - the bit higher than the Tdd needs to have a low Tdd; the 'kick' effect is only temporary, and more moisture is required as the 'kick' runs out. If you look at the last skew-t chart I posted for the SE, you can see all that is happening is that you'll get the kick towards the cloud tops, but as the moisture runs out, so will any high Tdd effect. In this case, perhaps an extra 30-50hPa of height on the cloud tops which may not even be visible.

Edited June 8, 2009 by VillagePlank

[VillagePlank]

Sorry guys, messed up the chart by linking Td to ELR. Bad mistake, and I can't edit my post, now. Here's the corrected chart, with the Tdd kick at 750hPa, 600hPa, and 400hPa. The best 'kick' is at 400hPa.

Sorry for any confusion

Edited June 8, 2009 by VillagePlank

[maidstone weather]

unconfirmed reports of rumbles of thunder in Cardiff - can anyone confirm?

Edited June 8, 2009 by maidstone weather

[andymusic]

unconfirmed reports of rumbles of thunder in Cardiff - can anyone confirm?

getting extremely dark from that direction and SAT 24 looks like somethings "converging" to produce brighter cloud tops above the south wales area

mind you - it'll have to go some to beat what we had last saturday

Edited June 8, 2009 by andymusic

[tinybill]

Check this out:

http://news.bbc.co.uk/1/hi/england/8089268.stm

I wonder when that happened exactly? As it doesn't say atm.

last night about 6.30 over the west side of suffolk their was some monster storms

[andymusic]

wind has picked up - very dark - moderate rain - just waiting for a rumble of thunder!

[Coast]

All the potential looks to be tantalisingly close today, but just over the Channel! ESTOFEX have some big red areas for central France but UKASF have a watch area that includes some of the SE and Western Ireland:

Storm Forecast Issued: 2009-06-08 21:16:00

Valid: 2009-06-09 00:00:00 - 2009-06-09 23:59:00

Regions Affected

( SE England and parts of East Anglia are included in the WATCH )

Synopsis

LOW pressure, centred over the North Sea at midday, will dominate the weather across the UK on Tuesday. Initially the associated cold and occluded fronts will provide outbreaks of rain across southern and eastern England primarily. Scattered showers and thunderstorms are forecast to develop over the nearby continent during the day.moving northeastwards - there is a slight risk of scattered showers/storms developing over Kent, Surrey, Sussex and Essex in particular, in response to convergence zones. However this risk relies on how quickly the occlusion approaches from the west - if the occlusion clears the UK before midday or soon after, then the risk of storms is significantly lowered. This will need monitoring during Tuesday. Scattered, mostly light, showers will also develop over western Ireland during the day. There is a slight risk of one or two thundery showers with these, but the risk currently remains low.

21st Operational Weather Squadron have virtually the same area with that tiny little bit of SE Kent just in the zone:

GFS also shows it just missing:

So it looks like we are relying on how quickly (slowly?) the occlusion clears us today

[BrickFielder]

Tomorrow we have an occlusion over central parts of the UK, now while this may just produce clouds it seems likely that cloud begin to break up during the afternoon. Winds will be coming up from the south bringing some moisture. Forecast SkewT's suggest quite high low level dewpoints which GFS can over do at times, so there may be a limitation there and the profile looks moist all the way up.

Despite low level wind speed shear being low, winds do look quite backed at the surface and there is a marked shift in wind direction through the mid layers. Any storms developing most probably will be short lived due to weak winds and tops don't look that high, but there might be a slight chance of convergence zone tornado formation.

Lots of ifs and buts, and some reasons why storms may not appear at all, but worth keeping an eye on.

[Coast]

Local BBC weather going for a lot of rain in Kent today but no mention of the T word

[Paul Sherman]

Met Office in the Process of Updating a "Be Prepared" Warning at the moment on their Site For Kent and Sussex

Paul S

[Coast]

Here we go Paul!

London & South East England: Brighton + Hove E Sussex Kent Medway

Heavy Rain 1145 Tue 9 1800 Tue 9

Outbreaks of heavy rain or perhaps thunderstorms are forecast to spread across Kent and East Sussex today with rainfall totals possibly 15 mm in 3 hours. 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: 0948 Tue 9 Jun

[maidstone weather]

Matt Taylor was going on about thunderstorms across Kent and Sussex this afternoon - will be interesting to see if it comes off, or if it's another BBC over-hyped event

What does "EC" stand for on the map posted by Coast?

Edited June 9, 2009 by maidstone weather

[Coast]

A different one from the usual, the South African Weather Service! :

[Coast]

What does "EC" stand for on the map posted by Coast?

ABSTOP Absolute Topography

BB OCCL Back Bent Occlusion

Bcl Bound Baroclinic Boundary

BL Boundary Layer

BOYD Boyden Index

CA Cold Air Advection

CCC Closed Cell Convection

CAD Cold Air Development

Cb Cumulonimbus

CCB Cold Conveyor Belt

CF Cold Front

CF in CA Cold Front in Cold Advection

CF in WA Cold Front in Warm Advection

Ci Cirrus

CISK Conditional Instability of the Second Kind

Conv Convergence

Cu Cumulus

Div Divergence

EC Enhanced Cumuli

FD Front Decay

FI Front Intensification

Inst Occl Instant Occlusion

IPV Isentropic Potential Vorticity

MCC Mesoscale Convective Complex

MCS Mesoscale Convective System

NVA Negative Vorticity Advection

OCC Open Cell Convection

OCCL Occlusion

PFJ Polar Front Jet

PL Polar Low

PV Potential Vorticity

PVA Positive Vorticity Advection

RELTOP Relative Topography

SH-index Showalter Index

Sc Stratocumulus

St Stratus

TA Temperature Advection

TFP Thermal Front Parameter

THR Thickness Ridge

ULL Upper Level Low

UTH Upper Tropospheric Humidity

WA Warm Air Advection

WCB Warm Conveyor Belt

WF Warm Front

WV Water Vapour

EC info: www.zamg.ac.at

Edited June 9, 2009 by Coast

[VillagePlank]

Wasn't aware that storms were a possibility today, . But Meto forecast very heavy rain or perhaps thunderstorms moving into the SE. Well, good luck to people in Kent

I prefer the chances for early next week Bound to have downgrades ...

[VillagePlank]

Yeah, just looked at the SB CAPE chart and well, it looks good :lol: probably will be downgraded to nothing, but it's still good to look at on chart, makes me imagine of what would happen if it pulled off :lol:

At the risk of mega ramping, CAPE always seems to be pulled S/E as it is downgraded ..... :lol:

CAPE is, unfortunately one of those parameters that can suddenly exist, and suddenly disappear, even on the day, which is why the soundings and subsequent skew-t charts are so important.

As for today, most of the parameters over Kent are not condusive to storm formation, I think. It's a 50/50 shot, in my opinion, but the deritus left over by what's going on over France may indeed drift this way, and, some, might get lucky.

[maidstone weather]

first sferic now popped up over France, but way too far east :lol:

[VillagePlank]

Yeah, just looked at the SB CAPE chart and well, it looks good :lol: probably will be downgraded to nothing, but it's still good to look at on chart, makes me imagine of what would happen if it pulled off :lol:

Well, the ensembles seem to agree at quite a significant warm up on the cards with 850hPa Tc some 10C up on today:

[Paul Sherman]

Latest Meto Update for 6-15 Days states becoming Warm or Very Warm with Perhaps Thundery Showers in the South East and East at the end of the Weekend and into start of next week.

You never know :lol:

[Koppite]

Well, the ensembles seem to agree at quite a significant warm up on the cards with 850hPa Tc some 10C up on today:

I noticed that too VP, and if i am reading the charts right (please correct me if I'm wrong,) there are some good peaks in the rainfall, especially on the London ensembles around the same timescale, which maybe indicate some thundery activity?

Edited June 9, 2009 by Koppite

[Harry]

Oh well, I'll take any possibilities for the weekend.

Not getting excited about today - if any thundery activity does come ashore, I'm too far West to benefit, or even distant flashes I reckon.

Roll on the weekend and into next week!

[Coast]

Nice lot of sferics kicking off in NE France and Belgium, now it's the waiting game......

[Harry]

So is the possibility then that thunderstorms/heavy rain will form over Benelux and then pull W around the LP in the channel?

Or that trough will come a lot closer? :lol:

Edited June 9, 2009 by Harry