Uk Convective General Discussion & Forecasts, 28th June 2012>

[Liam J]

Really strong July sun beating down here now, daytime heating kicking in shame conditions arent more favourable today. 19c and feeling very muggy.

Weather app says chance of storm, 78% humidity.

On my mobile hope this posts ok lol

Edited July 3, 2012 by Liam J

[Karl83]

Friday is a downgrade on CAPE values for my area http://www.wetterzen...cs/Rmgfs816.gif

However, Saturday is an upgrade http://www.wetterzen...s/Rmgfs1086.gif

Can anyone tell me what other charts I need to be looking at to forecast storm potential? Much appreciated.

EDIT: East looks good on Sunday http://www.wetterzentrale.de/pics/Rmgfs1326.gif

Edited July 3, 2012 by Thunder_Bolt

[Chris K]

It maybe a downgrade/upgrade run to run, but I think it is best to compare each run from other days e.g - 06z yesterday with the 06z today. You're bound to get changes on each and every run and it can still be unreliable on the very day.

Still looking decent enough with the threat of thundery showers for most areas at some point during the week/weekend.

Edited July 3, 2012 by Chris K

[chionomaniac]

That's the trouble when you have a SW'erly flow, onshore wind brings drier more stable air at the sfc off the still cool channel which tends to limit surface based CAPE across the SE. SE tends to do better in a slacker flow or westerly flows or when plumes with EMLs destabilise bringing elevated storms across the Channel from France.

Yes, this summer has seen an abundance of SW winds from low pressure situated further north. Any southerly component to the wind down here and we get dryer weather and the storms hit further north. I was hoping for the cut off lower to dig in a little further south and east to increase our chances but no such luck.

However for those who enjoy storms and live further north, good luck.

[Karl83]

It maybe a downgrade/upgrade run to run, but I think it is best to compare each run from other days e.g - 06z yesterday with the 06z today. You're bound to get changes on each and every run and it can still be unreliable on the very day.

Still looking decent enough with the threat of thundery showers for most areas at some point during the week/weekend.

Of course.

[Supacell]

Friday is a downgrade on CAPE values for my area http://www.wetterzen...cs/Rmgfs816.gif

However, Saturday is an upgrade http://www.wetterzen...s/Rmgfs1086.gif

Can anyone tell me what other charts I need to be looking at to forecast storm potential? Much appreciated.

EDIT: East looks good on Sunday http://www.wetterzen...s/Rmgfs1326.gif

I tend to look at CAPE/LI to get a measure of the ability of air to rise and how quickly. You also need moisture for clouds to form - may be wrong here but dewpoint gives a good idea of this. And of course you need a trigger, which can be a number of things - front, trough, wind convergence, orographic lift, cold air moving over the top of warmer air etc.

For more severe/organised storms there needs to be a way of the updrafts and downdrafts being separated (so parameters such as speed and directional shear) otherwise a storm will kill itself off within around half an hour.

Although a little more complicated, the skew-t diagrams are a good thing to look at as you can plot temperature and dewpoint and derive from that the approximate height that the air will condense to form clouds and at what height these parcels will stop rising for the cloud top height. The higher the clouds can rise then the better the chance of a thunderstorm.

There are some great guides on this site to learn from, i am still learning now

Edited July 3, 2012 by Supacell

[Steve C]

There are some great guides on this site to learn from, i am still learning now

Agreed, Supacell

[P-M]

Metoffice have early warning out for Northeast corner of the UK for persistant rain on Friday and Saturday but say over Northern England the rain will be more showery and thundery in nature with a risk of local surface flooding. One to watch out for.

[Liam J]

A snapshot of the Metoffice warning issued today for the potential threat of thunderstorms and flooding, notice the use of the word 'Thunderstorms' and not heavy thundery showers....

Edited July 3, 2012 by Liam J

[Aaron]

Don't get me excited Liam..

[Luke]

And a nice big gap between the two warnings

[mattyk1985]

To be fair though after last Thursdays affair the Metoffice didn't instill confidence in their thunderstorm forecasting.

[Liam J]

Don't get me excited Liam..

I'm getting excited already! I can feel it now, MEGA thunderstorms..... Come on Aaron woo hoo we're gonna leave the NSC

Edited July 3, 2012 by Liam J

[P-M]

A snapshot of the Metoffice warning issued today for the potential threat of thunderstorms and flooding, notice the use of the word 'Thunderstorms' and not heavy thundery showers....

Thats just changed as of 12.08 to say :

Some heavy and persistent rain is likely to affect much of southern, eastern and central Scotland along with much of northern England at times during Friday and Saturday. Over parts of Northern England on Saturday in particular, the rain may be of a more showery, thundery nature. The public should be aware of the localised surface water flooding is likely and there is an increasing risk of some river flooding.

[Karl83]

I tend to look at CAPE/LI to get a measure of the ability of air to rise and how quickly. You also need moisture for clouds to form - may be wrong here but dewpoint gives a good idea of this. And of course you need a trigger, which can be a number of things - front, trough, wind convergence, orographic lift, cold air moving over the top of warmer air etc.

For more severe/organised storms there needs to be a way of the updrafts and downdrafts being separated (so parameters such as speed and directional shear) otherwise a storm will kill itself off within around half an hour.

Although a little more complicated, the skew-t diagrams are a good thing to look at as you can plot temperature and dewpoint and derive from that the approximate height that the air will condense to form clouds and at what height these parcels will stop rising for the cloud top height. The higher the clouds can rise then the better the chance of a thunderstorm.

There are some great guides on this site to learn from, i am still learning now

Thanks very much.

I will have a look for the guides.

[mattyk1985]

I tend to look at CAPE/LI to get a measure of the ability of air to rise and how quickly. You also need moisture for clouds to form - may be wrong here but dewpoint gives a good idea of this. And of course you need a trigger, which can be a number of things - front, trough, wind convergence, orographic lift, cold air moving over the top of warmer air etc.

For more severe/organised storms there needs to be a way of the updrafts and downdrafts being separated (so parameters such as speed and directional shear) otherwise a storm will kill itself off within around half an hour.

Although a little more complicated, the skew-t diagrams are a good thing to look at as you can plot temperature and dewpoint and derive from that the approximate height that the air will condense to form clouds and at what height these parcels will stop rising for the cloud top height. The higher the clouds can rise then the better the chance of a thunderstorm.

There are some great guides on this site to learn from, i am still learning now

Its them skew-t diagrams that I can't get my head around.

[NUT]

Tomorrow and thursday looking OK. Friday/saturday we seem to be right on the border line (and we stay in the blue) but things will chop and change probably

[Coast]

Its them skew-t diagrams that I can't get my head around.

http://forum.netweat...kew-t-diagrams/

http://www.atmos.mil...kewT_HowTo.html

http://www.theweathe...m/thermo/qanda/

http://www.downunder...de/guide08.html

http://www.skystef.b...asting-tips.htm

http://www.skystef.b...ather-terms.htm

Why get a Sounding?

A Sounding (radiosonde ascent) returns the state of the atmosphere at a certain point at a certain time. Soundings find particular use in storm prediction. From them it is very easy to determine the stability and other parameters relevant to the storm forecast. The Skew-T Log P representation The most commonly used graphical representation of a radiosonde ascent is a very quick overview of the current situation. The temperature and dew point it at a 45 degree angle to the right described above and the air pressure in a Logarithmic scale for the Y-axis. The wind speed and wind direction are usually presented as a wind vane on the right. To be able to detect the direction of the wind speed with height better, I have attached the wind speed as an additional scale on the x-axis. The wind directions are shown as simple lines on the right. Example Another X-scale is the mixing ratio (mixing ratio). It is used to determine the condensation level. as additional scale addition to the directly measured values ​​(temperature, dew point, wind), CAPE and CINH be presented to a height of 700 hPa graphically. CINH it is multiplied by a factor of 5 in order to obtain acceptable values ​​for the graphical representation. (Description of CAPE and CINH see below) condensation levels in a sounding, you can choose between two different condensation levels: Lifting Condensation Level (LCL) The LCL is used to adjust the height of cloud base to determine if the convection through elevation of fronts or mountains is triggered. For this you need the average mixing ratio and the mean temperature of the upper air parcel. As a standard here the averaged values ​​of the lowest 100 hPa may be used. The intersection between the mixing ratio and the Trockenadiabate is the LCL. example Convective Condensation Level (CCL) The CCL is used when the convection is thermally activated. This is especially the case when heat thunderstorms. As with the LCL you need for that also the mean value of the mixing ratio. The intersection between the mixing ratio and the temperature curve from the measured values, the CCL. The CCL is usually higher than the LCL. example thunderstorm prediction using a Soundings can Soundings are in the storm forecast a significant factor dar. They can assess the situation more accurately and, most importantly, a statement which is to be expected for a type of storm. Because they represent only a snapshot of the atmosphere at a certain point, you should never just rely solely on the current sounding, but to attract more and also the models to look for modifications in the next few hours. First one looks at the best curve the rising air parcel (Parcel) and compares them to the temperature curve. Parcel, the curve is far to the left of the temperature curve, so the atmosphere is stable and there are not expected thunderstorms. The Lifted Index is a value often used to describe the current stability. A value of> +3.0 ° C in the sounding of 12Z is usually too stable for the formation of thunderstorms. Exception would be an approaching cold front with strong cooling in the amount or moist air, which flows into the lower atmosphere. At 00Z climb you have to watch more, because there already alone may be sufficient to sunlight the next day to destabilize the atmosphere. A second factor can be expected if the storm is moisture in the lower atmosphere. The Lifted Index can indeed be negative, but dry air near the ground impossible storm, since a is not to be overcome cap, which means that rising air parcels can not reach the "Level of Free Convection (LFC)," unhindered by which to them would rise. example for a strong thunderstorm Cap. ermitten The third important parameter for thunderstorm, the raising, can not be a sounding. Therefore, the model maps should be consulted. One sign of improvement can be at most one clockwise rotating wind direction. In the lower atmosphere, it points to warm air advection, which would mean raising. Want to find out what is expected for a type of storms, I just happened to be the first the wind profile. No greater increase of the wind with height can be seen, one can assume that will only make short-lived storm, its intensity is determined by the instability. At high instability is expected to multi-cell, single cells at low instability. example of a multi-cell Soundings. If a wind speed reaches at least about 40 knots at 300 hPa, there is the possibility of thunderstorms with a longer lifetime (supercells). The increase of wind with height is crucial to create a separate area from upwind downwash. For an additional clockwise rotation of wind with height supercells are very likely. The question whether this could happen in conjunction with supercell tornadoes can be as far as answering that the chances are for the largest, if a strong low-level jet is present. The low-level jet usually occurs in advance of cold fronts, where large temperature differences develop in the deeper layers of the atmosphere. In Switzerland, the Low-Level Jet at its maximum at about 700 hPa ( example ). The Jura and the Alps to have a significant impact. In rare cases it happens, however, that the low-level jet has its maximum already at about 850 hPa. Then, in supercells and tornadoes of connection possible (are as ). Sounding parameters from the measured values ​​of a radiosonde ascent can calculate all sorts of different parameters. With them, then the structure of the atmosphere to be assessed more precisely. Below are all the parameters in brief, are shown on the right side. 850 Wet Bulb Theta-E energy content of air at 850 hPa Sfc - 700 One Rel Hum Average humidity between the ground and 700 hPa Convective Temperature Exceeding this temperature near the ground is expected to trigger thermal convection. example Lifted index difference between the ascending air Packet and the measured ambient temperature at a height of 500 hPa Example formula: LI = T500 - T500Parcel

http://www.skywarn.c...u_sounding.aspx

[Karl83]

http://www.weatherfaqs.org.uk/

For those still learning, like myself.

[Bobby]

The NMM shows some heavy/thundery downpours moving across the E of England early Thursday, moving up from the continent

[Mapantz]

There may be a good chance i can salvage something from the lack of thunderstorm activity here, i like the look of lowering heights down here in the south west. Parts of Cornwall, Devon, Somerset and in to the Bath area will be the best places down this way, but the other concern is rainfall .. some large totals could be had due to the slack wind flows.

[Thermohaline Conveyor]

Friday looks good right now, plenty of deviation regarding (CAPE), but a slack cyclonic flow will mean plenty of PVA and VORTMAX lobes oscillating

[NO LONGER POSTING]

Friday looks good right now, plenty of deviation regarding (CAPE), but a slack cyclonic flow will mean plenty of PVA and VORTMAX lobes oscillating

In other words..THUNDERSTORMS

[SteveB]

Surely its our time for some proper thunderstorms.

[Thermohaline Conveyor]

In other words..THUNDERSTORMS

In a sense yes