Detailed Convective Discussion, Forecasts And Analysis

[BrickFielder]

Not really that hopeful for most of the UK today. The exception being Ireland. Mid level lapse rates are pretty poor.

Some suggestions about the north east getting some storms around, but looking at the forecast SkewT's I am not that impressed.

Obviously this area does come under an area of synoptic lift, so it is possible to get an isolated storm, and these forecast SkewT's can be wrong , but on this basis I would not be that keen.

Instability appears to be pretty limited.

If I was to pick soemwhere I think I would look at somewhere like north wales.

Instability is weak, but you could just about get a low topped storm from that SkewT.

Looking at the Satellite pictures there are a couple of bright cells to the west and south west of Wales which make me think that there could be some fast moving heavy showers sweeping in from the south west. These types of cells might be worth watching for Wales and just maybe western parts of England.

Low risk storm day, but if I had to pick somewhere then it might be Cardiff and on towards the Worcester area and again from north wales on toward Liverpool post frontal.

[Methuselah]

Thanks for that, BF. Any greater chance tomorrow, do you think?

[Stuart]

Storm Forecast Issued: 2011-06-07 22:42:00

Valid: 2011-06-08 00:00:00 - 2011-06-08 23:59:00

Regions Affected

Scotland, N England, N Wales and Northern Ireland

Synopsis

Low pressure "Balthasar" (FU Berlin) will linger across Scotland during Wednesday. Low geopotential heights combined with very cold mid levels will be present over much of the country, steeping lapse rates.

Up to 600 J/kg CAPE to develop, with widespread showers and local thunderstorms over much of the country, the best of any thunder/lightning primarily across Scotland, with ELT's as low as -40°C.

Meagre deep layer shear is likely to inhibit the threat of a tornado/funnel somewhat, although lighter winds across Scotland and Northern Ireland will allow prolonged torrential downpours to cause localised flooding. Hail is likely in many of the showers, locally moderate in size over Scotland, Northern Ireland and

http://www.ukasf.co....orecast/id-370/

[knocker]

Excuse my ignorance but how are the forecast SkewT's generated and what initual environmental profiles are used?

I'm assuming, probably incorrectly, that they are based on the forecast temps and dew points for the standard upper air levels.

Edited June 8, 2011 by weather ship

[Stuart]

Storm Forecast Issued: 2011-06-09 22:01:00

Valid: 2011-06-10 00:00:00 - 2011-06-10 23:59:00

Regions Affected

(United Kingdom, excluding S Wales & SW Eng, is included in the WATCH)

Synopsis

Cold mid levels will overspread the country on Friday, associated with an upper-level Low ("Balthasar" (FU Berlin)). Relatively low geopotential heights combined with surface heating will aid steeping lapse rates.

Up to 700 J/kg CAPE is expected to develop, with widespread showers and local thunderstorms over much of the country, although it is anticipated that the best of any convection will occur late in the afternoon and early evening, with ELT's as low as -30°C.

Meagre deep layer shear is likely to inhibit the threat of a tornado/funnel somewhat, although quite a few local convergence zones are expected which increases the chance of convergence-type funnels. Hail is likely in many of the showers, locally moderate in size over England in particular.

Showers will slowly decrease in coverage during the evening, becoming mainly confined to eastern and coastal parts by the end of the forecast period.

http://ukasf.co.uk/m...orecast/id-371/

Edited June 9, 2011 by Stuart

[BrickFielder]

Mixed bag of opportunities for storms today. Over riding driver will be steep mid level lapse rates spreading eastwards.

Upper level divergence occurs comming in from the east but is coming in later.

Instability is fairly low until mid afternoon and then picks up into the early evening.

Low level convergence Zones are likely to play a focus for storms.

Potential areas for me would be South Wales mid afternoon to early evening. An area through the Midlands moving southwards during the late afternoon. Scottish borders, Ireland during the afternoon. East Anglia, Lincolnshire and possibly just north of London early evening. Since winds are generally weak going up through the atmospher the chance of a sustained tornado is poor, but convergence zones especially around north norfolk and Lincolnshire could support a weak short lived tornado (Caveat being updrafts may not be strong enough). Although I think cloud cover will hinder developments across the midlands at times since things are likely to be messy due to plenty of moisture aloft, late afternoon in the western part of the west midlands could prove interesting.There is also a chance of embedded thunderstorms in the rain band moving across the south west.

Forecast SkewT's show a mixed bag with best instability probably across the midlands moving eastwards.

Notice how the winds turn in the lowest level around Kings Lynn, but instability is fairly poor. Low freezing level means hail will be a risk again.

Cloud cover will be key again, which may hinder some development. So plenty of opportunities some of which may come off.

Best of watching the radar and satellite pictuires from here on in.

[BrickFielder]

There are a number of areas to consider today, although generally instability looks pretty poor.

Perhaps a prime interest area today would be parts of eastern scotland, where there is likely to be a little instability with light but turning winds in the lowest level. This could be good conditions for a weak short lived tornado to develop.

Another area to watch will be Kent and east anglia where we might get some destabilisation during the afternoon. Turning winds through the mid levels although weak are interesting although low level wind shear is generally not enough for tornado devlopment and updrafts will nto be that impressive a storm developing at an outflow boundary could in theory produce a tornado. Overall it seems unlikely to me.

Next up is eastern parts of Wales perhaps stretching up to Manchester and the south west. Since there is some mid to upper level wind divergence strecth through from Ireland across this area late on and the troposphere boundary will be quite high there is a chance of some isolated storms. Vorticity charts suggest development in a line downstream of upland areas of Cornwall and Southern Wales.

Conversely instability looks pretty non existant although some vertical velocity is suggested.

Isolated and late afternoon could see some heavy showers.

Overall its not that impressive, although I rather fancy someone in eastern scotland spotting a weak short lived funnel (maybe not touching down). Eastern England maybe a bit too messy for strong storm development and instability over the west may be too weak. I think I prefer the prospects on Saturday. In other words watch the radar and see how things develop is the best option now.

[DanN]

I wonder if somebody would be able to help with a question...

I'm looking at the meto fax charts for tomorrow, which show a trough from roughly the wash down to the south west. How would you go about picking these out on the NW extra charts? I'm guessing with a combination of the vorticity and vertical velocities but I can never really work it out or nothing really stands out to my untrained eyes! I can see there is some vertical lift showing and that it moves eastwards (I guess with the trough) but is there more to it than that? Any help would be appreciated, thanks.