Thunderstorms and Convective Potential

Snowbie

Post here of all things thunderstorm related,whether it be radar,maps,charts,forecasts or just simple discussions.
Over the months you will find some variables or terms describing suitability of storms which are:
CAPE - This is the amount of potential energy in the atmosphere. High CAPE will indicate a high chance of thunderstorms.
LI - Lifted Index (LI) displays the 'trigger' potential at the surface to initiate unstable conditions. A low or negative LI will indicate conditions for thunderstorms are favourable.
Cb-Cumulonimbus or thundercloud.
Anvil-Where the top of the Cb reaches the stratosphere and spreads out like a flat top.
Cell or Supercell-An individual storm or a violent storm.
Squall line-Multi cellular organised storms forming in a line usually ahead or parallel to cold fronts.
Embedded Storms-Storms that are contained in overcast conditions
Convection-Warm air rising,cools,condenses forming cumuli clouds.
Orographic lift-Low level winds are forced to rise against rising terrain ie:mountains.Prevailing wind on a hot summers day,this lift can produce rapid convection.
Convergence zone-usually refers to a region in the atmosphere where two prevailing winds meet and interact, usually resulting in turbulent weather.
Lapse rate steepeing-is another fancy term for instability.
Sferics-Sound of low-frequency radio signals that derive from lightning strikes.Common terms would be strikes or strokes.
Some useful links
http://www.irlweather.com
http://www.gyweather.com/
http://www.isleofwightweather.co.uk/live_storm_data_sound.htm
http://www.wetterzentrale.de/pics/Rsfloc.html
http://www.estofex.org
http://www.blitzortung.org/index.php?mode=0&map=5&lang=e
http://www.nowcast.co.uk/lightning/
http://meteocentre.com/lightning/map_sfuk.php?time=0&lang=en&map=Europe
http://www.estofex.org/guide/
http://www.strikestareu.com/
If anyone has any more feel free to post them.

Snowbie

New thread for up and coming potential for storms over the next couple of days.
With a trough crossing the country from early morning to late afternoon, heavy showers will break out widely with the eastern half of the country getting the heaviest. Weak Storms are likely in this region.

Surface based Cape and LI remains moderate across the eastern half of the country. Conditions at the surface with energy and a trigger looks favourable.

Cape (energy) in midlevel regions are also favourable.

500mb RH% is around 85%, so moisture be evident in the atmosphere at high levels 5km.

Instability(lapse rates steepens) throughout the morning and peak mid afternoon continuing into the evening. East with highest values.

Convective precip for 15Z showing the total rainfall around that time.

Snowbie

Shearing wind speeds(both vertical and directional) keep a storms longevity ongoing. Basically it seperates the updraft and downdraft in a storm. For Wedensday there is little low level shear aswell as deep level shear suggesting that any storm that occurs will be weak in nature and will not last long as the downdraft falls back on the updraft. But the odd moderate storm cant be ruled out.

Dewpoints and surface temps are borderline but just on the right side for development.

Storm risk is a cautious 50%

paulhac

Thanks Snowbie for the update re wx for tomorrow. Have been looking at boards weather and other wx forums for sometime now including TWO, UKweatherworld ,Netweather etc. decided to start posting here. keep up the good work with your analysis. Cheers. Looking forward to tomorrow.
Paul

Snowbie

Welcome to the forum Paul.:)

We had 2 long loud claps of thunder at about 430am this morning followed by a couple of micro bursts of heavy rain.

Snowbie

Not much change to the above. Risk maybe a little more south this morning. Overnight a second chance of storms or heavy showers towards the south coast and into the SE may drift in off the Celtic sea.

Tomorrow looks very interesting with lots of energy moving into the SW from about 06Z and moving up through the country.

Looks like these intense showers are popping up out of nowhere.
just had a 47mm+/hr short burst here.
No thunder this time

Snowbie

Trough moving through the centre of the country atm and as i mentioned in the last thread, extra lift is now being provided by hilly areas.Showers have broken out ahead of the trough. A second line of showers has moved into the west also.

paulhac

still quiet here in Dublin but sky darkening now (10.20). radar shows showers heading north out of Wicklow towards Dublin.

Damomanye

massive heavy burst of rain here in the last few mins.

Snowbie

Cb's starting to push up through the cirrus on the sat pic also first bits of lightning detected.

http://www.sat24.com/frame.php?html=view&country=gb&sat=vis

Pouring down here now.

paulhac

I think the showers will be deflected away from dublin around the mountains so am not expecting much out of this set up . they are moving NE, always a bad sign for Dublin!!!

Snowbie wrote: »

Cb's starting to push up through the cirrus on the sat pic also first bits of lightning detected.

http://www.sat24.com/frame.php?html=view&country=gb&sat=vis

Snowbie

These situations are nowcasting. As expected the showers are taking a south to north motion. There is little convection around today and the trough is just peping up the showers merging them together now. As the peak CAPE is due mid to late aftenoon, there is still the chance of forcing over the mountains for a few downpours around Dublin due to southerly winds. Nothing special though just the odd rumble or two.

Radar and sat watching.

Hal1

That'll be the forcefield around Dublin again, everytime we get a sniff of a bit of a TS it's shields up!

Snowbie

Met.ie wrote:

Further heavy showers and thunderstorms spreading up from the Southeast tonight. Clear spells with lowest temperatures between 9 and 12 degrees. Some mist or fog patches as winds become very light.

Looking at the 06Z, the SE or south was more at risk only. 12Z be interesting.

Snowbie

Some beefy looking showers heading for the Dublin area on the radar building up over the mtns.

forkassed

Had a heavy shower about 15mins ago in ballybrack and another heavy lookin shower on the horizon

Hal1

Some fierce looking clouds just passed to the north of hear. I wouldn't be suprised if they gave a rumble or two. Some CB's devoping in the midlands. http://www.sat24.com/frame.php?html=view&country=gb&sat=vis

rc28

After a heavy shower there I just heard a rumble of thunder

rc28

Another few rumbles there from a shower to the east of me

Snowbie

Snowbie wrote: »

Looking at the 06Z, the SE or south was more at risk only. 12Z be interesting.

On what are the Met basing their forecast of heavy showers and thunderstorms moving up from the south east tonight?

brettmirl

About 4 loud claps of thunder to the south of Ashbourne.

Sun shining in the village after a heavy shower, but very dark clouds to the south.

Hal1

I've been glued to Snowbies detector http://www.irlweather.com/StormVue.html

ch750536

Power just went off for a few secs here. The norm though, seems long hair and one balloon can cause an outage.

Snowbie

Snowbie wrote: »

Not much change to the above. Risk maybe a little more south this morning. Overnight a second chance of storms or heavy showers towards the south coast and into the SE may drift in off the Celtic sea.

Tomorrow looks very interesting with lots of energy moving into the SW from about 06Z and moving up through the country.

Snowbie wrote: »

Looking at the 06Z, the SE or south was more at risk only. 12Z be interesting.

Deleted User wrote: »

On what are the Met basing their forecast of heavy showers and thunderstorms moving up from the south east tonight?

This is it BB i dunno. Mentioned myself earlier of a threat to the S and SE from the 06Z but i don't see anything as yet to pose a risk to the rest of the country. Havin looked at 12Z yet.

M.T. Cranium

Move this to a better thread if you want, but as I am somewhat new to Irish weather watching, can somebody tell me what the heaviest rainfall amount for one storm has been in the past? And also, has there ever been a significant tornado in Ireland, where and when? I have to imagine there have been smaller ones so let's say anything at F2 or higher such as they had in Birmingham in July 2005. And while you're at this, what is the highest temperature ever recorded in Ireland? I know it wasn't in 1978 (that was the one time I had the honour of attending the rain festival).

NewsWire

hey all, i got a report through email of serious flooding in Rathkeale in Co. Limerick due to a massive deluge there in the last few hours.

paulhac

http://www.wetterzentrale.de/topkarten/fsfaxsem.html

Bracknell chart for 12z today shows trough line just off the south coast. this must be tonights showers. Just click on Bracknell on the FAXlist

rc28

More thunder and dark clouds approaching here from the south

rc28

Torrential downpour now.

ch750536

http://www.metoffice.gov.uk/weather/uk/radar/index.html



Rarely see red there, looks like the Rathkeale reports may be correct.

Hal1

Malin Head reporting rain/thunder, thats the first report I've seen on met.ie today of storm related activty, it must be near the station. Drizzly here moderate at times, feels really heavy in the air.

Sierra Oscar

There are some astonishing black clouds coming our way from Limerick City at the moment.

nacho libre

I've been taking some pictures of what looks to be a developing thunderstorm to the west of me. These cb clouds are impressive!

Snowbie

Snowbie wrote: »

This is it BB i dunno. Mentioned myself earlier of a threat to the S and SE from the 06Z but i don't see anything as yet to pose a risk to the rest of the country. Havin looked at 12Z yet.

This is the thing that annoys me about met.ie lately.
Their sheer guesswork.
the amount of times they chop and change on the same day (I wouldn't mind if they changed 24-36hrs and stuck to that change)
We are doing a better job with all due respect and we are amateurs/enthusiasts.

Anyhow...now they've had a look out the window and at the radar... :rolleyes:

They say the following "Further heavy or thundery showers tonight, with all areas at risk. Lowest temperatures 9 to 12 degrees, with some mist or fog developing." No mention of where it's spreading from..

ch750536

Sierra Oscar wrote: »

There are some astonishing black clouds coming our way from Limerick City at the moment.

Was looking at that during dinner. Very imposing, very black.

nacho libre

False alarm on that developing thunderstorm.:o All there was out of it was a downpour.

Are these thundery showers that are forecast for tonight spreading across the country from the South East? Or has that weather forecast now changed?

Hal1

Just had a look at the forecast from Estofex.

"Latest GFS and WRF indicate quite strong instability in the range of the trough axis due to daytime heating, and showers and thunderstorms are forecast to form. Given weak vertical wind shear, some spouts :eek: may form especially over Ireland during the day."

Tomorrow could be our day in the east.

Supercell

Hoping so, am off work tomorrow and am gonna go chasing i think:)

Snowbie

From the 12Z output, the vertical wind shear speed is very weak at 3 m/s.

A bit better than today in terms of directional shear to tilt a storm but with little vertical speed shear, no severe storms.

Cape and LI pretty much same as today.

Cloud cover put a dampner on todays convection with the upper trough pepping up the showers only. With no convection it just didnt get that final push.Orographic lift played it's part in building congestus.
High level cirrus moving up from the south and with the unstable air with convective cloud meant that no sun could heat our land sufficiently enough to build widespread Cb's.

Tomorrow should be a bit clearer.

Cbstar

Met have to account for the whole country which is far more difficult than small areas

StratoQ

Good TS over Kilkenny City now. Went for a walk about 10 mins before hand but quickly ran back when I saw what was about to arrive!

Several stikes and some very intense rain (My rain gauge logged intensity at 136mm/hr).

Seems to be heading slowly north. You shud be next Danno!

Snowbie

Speaking to Danno now on MSN and he stays "looks like its between ballyragget and freshford"

Danno

One fork lightning here a few minutes ago.

Danno

Watched it from the attic velux. I thought it would fire up when it hit the east nore valley - the ridge from Ballinakill to Jenkinstown. Nothing still.

Danno

StratoQ wrote: »

Good TS over Kilkenny City now. Went for a walk about 10 mins before hand but quickly ran back when I saw what was about to arrive!

Several stikes and some very intense rain (My rain gauge logged intensity at 136mm/hr).

Seems to be heading slowly north. You shud be next Danno!

Hmmm, looked close enough to me here, but then again it was getting a bit darker. The edge of the rainfall area just clipped me here and headed more towards Castlecomer.

StratoQ

Well, Danno. I can vouch for the accuracy of your lightning detector anyway. The 10pm strike here (green triangle) was spot on. Green I take it means "negative"?

Snowbie

Another upper level trough will cross Ireland early on in the morning, once again.Showers from the word go through the south and SW will become widespread.
Depending on cloud cover, surface heating(if sun is out) will enhance convection and allow cloud tops to build up high. In any case slow moving heavy showers can be expected throughout the country but the south midlands and later east and north are at risk of a storm or two.
Showers subsiding by mid evening.

Although vertical and directional wind shear is slightly stronger than Wednesday, it is still very weak so storms be weak pulse type in nature.

Attach:Cape(SB and ML) LI and instability again favourable for hefty showers.

Storm risk a cautious 50%
Convective rain across the region at 15Z

Danno

StratoQ wrote: »

Well, Danno. I can vouch for the accuracy of your lightning detector anyway. The 10pm strike here (green triangle) was spot on. Green I take it means "negative"?

Negative intra-cloud. Good to hear that! Myself and Snowbie were concerned about the angle of placement one night. I made an educated guess for 175 degrees south, later a compass backed it up as 170. So we re-adjusted it and accuracy seems quite good since.

Mind you the further away storms are the more relevant the degrees become.