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://durrow.athost.net/lightning/
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://www.estofex.org/guide
http://www.strikestareu.com
If anyone has any more feel free to post them.

Snowbie

Will update the links above later and add more info above.

Just in time for the kiddies to go around the doors for Halloween, looks to be an area of greater instability crossing the Irish sea later on this afternoon and evening to affect any where on the east coast.

Hail a definite risk later with lightning a concern. Could be a repeat of yesterday evening when showers pepped up in late afternoon just offshore.
Data from the 00Z output.

With the day thats in it, hope this changes.
Met E have the risk increasing on their site for later on.

Many places dry with long sunny periods today but showers will affect western parts of Ulster and Connaught, as well as east Leinster. Some will fall as hail and the risk of isolated thunderstorms will increase near Irish Sea coasts. Moderate to fresh, northeast to north winds will keep it feeling cold; highest temperatures 6 to 9 degrees Celsius.

Sat and radar watching to see where these will come onshore.

Supercell

Plenty of hail showers passing through here and appear to be growing in intensity.
Wouldn't be surprised at all if there was thunder later.

Kippure

Serious shower activity coming through north of england, will pep up as it cross,es the irish sea. Some action later on this evening and tonight.

Snowbie

GFS 12z has played down the risk somewhat and pushes the threat a bit more south but there is sufficient Cape out over the Irish sea so always the chance of showers building and blown in with the onshore NE wind.

Danno

Lovely views of anvils far away to my east this morning around 11am. Pity I didn't have a camera. I looked up sat24.com straight away afterwards and seen them over Bray/Greystones area on the image. They must have been VERY high anvils to see them here over 60 miles away.

Fair bit of lightning here in the last half hour.
It's watery cloud to cloud stuff in the heavy shower we are having.
I'm afraid my rain guage has to be seriously under performing-I reckon the scales just are stiff and not tipping as quickly as they should be as theres been a lot of rain here this afternoon.I'd guess 7 or 8mm not the 2.8mm supposedly recorded.

Snowbie

Left over instability from NE UK has traveled over the Irish sea and is being peped up once again. Convective showers so i would expect some more hail in this.

This line of showers is about to come on shore in Dublin N+S and move SSW towards Wicklow.
However they don't seem too intense.

Edit: they have intensified just offshore and are moving in now in latest radar.
Can see the showers approaching.

paulhac

Thanks for those radar shots Snowbie. They have moved through here in glasnevin. no flashes though!

Mr Benevolent

I see that Saturday night is a possible candidate for a bit of flashbang fun!

Snowbie

From GFS 12Z output earlier.

A very strong Jet to the south of the country. Conditions ahead of this are very turbulent.
A moderate potential of storms for the west and NW in particular. A rumble of thunder can't be ruled out in the east(low potential atm) with a favourable atmosphere after midnight Saturday and into the early hours Sunday morning.

Trough approaches the west Saturday evening and crosses the country in the late evening destabilising the atmosphere ahead of it(forcing) and in its wake also introducing much colder air aloft also aided by nocturnal cooling of the cloud tops creating lots and lots of ice.
(Ice is an important ingredient for lightning)

18Z has slightly backed off but the potential i think will be increased in later runs.

Cape and LI shows decent amount of energy in the atmosphere.
Lapse rates drops significantly (Instability)
Low and deep layer shear indicating a good longevity to storms if they where to occur and
TT index (or Total Totals, anything over 45 is good) showing CB development and possible if storms to become strong, if they where to occur,
other parameters look good.

Nice to have charts like that in a summers afternoon sometimes.

Mr Benevolent

Dublin seems to be just on the edge of the good stuff, tantelisingly close as usual!

Thanks for the explanation, Snowbie. Always good to know why this stuff might happen!

M.T. Cranium

With the front rapidly approaching watch for hail, some thunder, and very gusty winds developing across the southern half or perhaps more of the country, winds should veer rapidly to WSW and this is where the strongest gusts may be recorded (60 mph possibly). Should be moving across in the next three or four hours.

kerry1960

Arriving shortly ....

Mr Benevolent

Feck. How long would that take to reach the East coast? 3 hours maybe?

Does the radar measure rainfall or cloud water content? Silly question I know, but I'm curious how clouds could keep up that sort of rainfall for such a long time.

kerry1960

Its seems to be intensifying....

kerry1960

Short and sharp

My back yard atm....

rc28

http://theweatheroutlook.com/twocommunity/forums/t/21721.aspx?PageIndex=2
Apparently the same front over us is a squall line- anyone in the west experience sudden severe gusts as the rain arrived?
Use the metoffice radar as it's far better at showing up the echoes and the meteireann one always underplays precip over NI (play the loop and look at that white blob develop over leitrim, tyrone area-tstorm?)

Supercell

They are really ramping this up on TWO
Must admit I'm looking forward to it

Deep Easterly

Black as hell here now. 2.4mm in last 5 mins.

nacho libre

rc28 wrote: »

http://theweatheroutlook.com/twocommunity/forums/t/21721.aspx?PageIndex=2
Apparently the same front over us is a squall line- anyone in the west experience sudden severe gusts as the rain arrived?
Use the metoffice radar as it's far better at showing up the echoes and the meteireann one always underplays precip over NI (play the loop and look at that white blob develop over leitrim, tyrone area-tstorm?)

it's been quite gusty here all right. it would have been a nice experience to be out in the middle of a field down in belmullet this morning

ian_m

My Meteox and Met Eireann radar composite shows one of the most intense bands of rain I have seen in a while. Forecast after the RTE lunchtime News warned of flooding in places. This could be interesting.

ninebeanrows

Yea looks like there will be an intense squall line!

Be on the look out for tornadoes and gustnadoes:pac:

Deep Easterly

Violent rain shower here now yippee!!!! Blackest afternoon I have seen this year!!!!

Edit: up to 10.3mm and rising..

nacho libre

Deep Easterly wrote: »

Violent rain shower here now yippee!!!! Blackest afternoon I have seen this year!!!!

fecker:D

Snowbie

Cold front moving across the country and looks more ragged on sat pics but precip on radar has it intensified somewhat in the last half hour.

http://www.irlweather.com/wxsatellite.php

00Z GFS hi res wants to intensify this into a possible squall line as it moves more eastwards across the country with forced ascent ahead of it. Seems to be doing so.
Atm from sat pics, cloud tops don't seem to be too high but should do so as this front moves east.

Cape and LI look to be only locally favourable due to the forcing and could be in a spell of quite heavy rain through midlands and east in the next couple of hours.

For the west using the sat above, look at the CB's dotted out over the N Atlantic that has your name on it later. Watching a possible trough forming from from this later. Nowcast using radar and sat pics.

Gusty winds and possible lightning but more an active cold front than squall line atm. It's not too well defined as yet.
Shear is well favourable.

ch750536

That was some rain, was caught in it at about 12:50 in Castleisland.

For 5 minutes was probably the highest rain rate I have experienced.

Snowbie

No squall line development, winds are very gusty in the passage of the front.
The most intense rainfall looks to be over Monaghan and Cavan. The odd rumble of thunder can't be ruled out from the odd embedded Cb.

Getting some sferics out west from showers moving in but nothing much atm.

highdef

Well I went to the effort of setting up my video camera. Obviously means that this will be a non event here. Looking that way at this stage. Only exceptional thing is how dark it is!!!

Snowbie

Front has intensified over the Celtic and in towards SW UK. Might be better fun over there later on. Sferics staring to get going down there.
NI has torrential stuff also but nothing up that way yet.

ninebeanrows

We got done yet again!

Look at that radar composite! Sickening

There sure situated our capital in a great position mind you.