Thunderstorm/Convective Watch: Autumn 2010

Trogdor

Please post any reports of thunderstorms or convective developments here along with any discussion of forecasts and convective potential.

A few terms which may come up in discussions.
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.

And a few useful links that I've collected up over time (feel free to post some more)
Current sferics:
http://andvari.vedur.is/athuganir/eldingar/
http://meteocentre.com/lightning/map_sfuk.php?time=0&lang=en&map=Europe
http://www.meteo64.org/orage/ (France and far southern England only)
Forecasts:
http://www.estofex.org/
http://ukasf.co.uk/module-Storm/
http://www.torro.org.uk/site/forecast.php
http://www.keraunos.org/prevision-orage-tornade-france-convective-outlook.htm (France Only)
Charts:
http://lightningwizard.com/maps/
http://www.wetterzentrale.de/topkarten/
http://mapserver.stormcenter.eu/
Guides:
http://www.estofex.org/guide/
http://spotterguides.us/basic/basic02.htm
http://www.theweatherprediction.com/severe/ingredients/
Radar/Sat:
http://www.met.ie/latest/rainfall_radar.asp
http://www.metoffice.gov.uk/weather/uk/radar/
http://www.meteox.com/h.aspx?r=&jaar=-3&soort=loop1uur
http://www.sat24.com/gb

Deep Easterly

61-90 average number of days with thunder for each month from October to Feb at each of the long-term met eireann synoptic stations:



Data Source: Met Eireann Climate Averages & Extremes

jimmynokia

there was thunder storms in clondalkin this evening

Su Campu

Nice glossary and list of links there trogdor.

Just to clarify Lifted Index. It is the temperature difference (in °C) between the environmental sounding and parcel sounding at 500hPa, ie. how much warmer a parcel of air raised from the surface to 500hPa would be, compared to the actual surrounding air at that level. If the parcel is warmer than its surroundings, then it's positively buoyant and will continue to rise. In this case the LI is negative (ie. the environment is colder than the parcel).

LI = Temp500 - Tempparcel

Yesterday we had LI around -3°C, which was enough to generate those thunderstorms. I don't know what the record is here, but in the States, values below -10°C can be found.

skipz

I mostly think of thunderstorms as a summer time thing, surely we wont get to much action in the cooler months?
I cant recall much, or any around my area last year in Autumn.

Su Campu

skipz wrote: »

I mostly think of thunderstorms as a summer time thing, surely we wont get to much action in the cooler months?
I cant recall much, or any around my area last year in Autumn.

You say that as if we get a lot in the summer months! :pac:

It's interesting that Valentia gets the most winter thunderstorms. That would be due to its proximity to the warmest sea surface temperatures and the wintertime jetstream. A cool airmass over a warm sea, with support from the jet above, will give the best chance. Over land in the winter, there is little surface heating and hence meagre low level instability.

Mr Benevolent

I was amazed at the storms we were getting in Brisbane last year when I was over there. 3600 CAPE and -11 LI!

skipz

Su Campu wrote: »

You say that as if we get a lot in the summer months! :pac:
.

I only got my first thunderstorm of 2010 yesterday;), but you know what i mean its really something that normaly happens in the warmer months of the year.

Redsunset

Roll on the THUNDERSNOW!!!!!!!:D

Causes of Thundersnow

What causes thunder and lightning during some snowstorms? Those who study the formation and life cycle of thunderstorms forming during the warm season understand that a strong, warm and moist updraft is a necessary condition.

In the warm season, these updrafts generally arise from the surface, but they need not. It appears that only those thundersnows developing over bodies of warm water arise from warm surface air. Most others, particularly those observed in the US central states, develop when the necessary convective process starts at higher altitudes than the surface air layer.

The two most important mechanisms for producing most thunderstorms are layers of instability — a region of the atmosphere with a tendency to promote upward air motions — and strong dynamic lifting — factors other than buoyancy that move air upward. Working in tandem, these two mechanisms provide that lift necessary to turn a precipitating cumulus cloud into a towering, lightning-producing cumulonimbus.

In a warm-season, airmass thunderstorm, the atmospheric instability needed to start the process begins at the sun-heated ground. The moist air warmed at the surface becomes less dense (more buoyant) and begins to rise high into the sky, a process known as surface convection. The less dense the air is relative to the surrounding air, the higher and faster it will rise; in such cases we have a deep layer of surface instability.

But in the cold season, and particularly in air conducive to snowfall, the lower troposphere is dry and cold which makes it relatively stable and inhibits parcels of surface air from rising. However, the troposphere can have many layers of distinct airs with differing vertical thermal gradients (called lapse rates), and when a layer of warmer, moist air wedges its way between a surface cold layer and colder air above, a region of elevated instability forms that may give rise to elevated convection, the convective rise of air beginning at an altitude above the surface. The effect is enhanced when there is cooling in the middle troposphere layers above the warm air wedge to enhance the convection potential.

An example of elevated convection at an occluded front resulting in thundersnow.

There are several mechanisms that can cause strong dynamic lifting of air (which I look at in more detail in What Goes Up: Introduction to Updrafts ). When one of these occurs in an atmosphere that has layers of instability, it becomes a trigger for air to begin rising and continue to do so. In this manner, strong updrafts are formed. The lifting can work on elevated layers as well as surface layers and thus produce elevated convection. In the most intense cases of dynamic lifting, such as air forced over a mountain range, the resulting cumulus clouds have all the characteristics of purely convection cloud formation.

In late fall and winter, when cold air moves across the relatively warm waters of the Great Lakes and other large water bodies, intense convective storms often develop that drop snow upon reaching the downwind shores (see Lake-Effect Snowfall on this site). When the waters are significantly warmer than the air, they act similar to the solar-heated ground in the summer and form surface convection. Under these conditions, intense cumulonimbus cloud development may arise that induces lightning flashes. When these snow squalls strike with heavy snows and gusty winds, they are punctuated with flashing lightning and booming thunder, i.e., thundersnow

skipz

Thundersnow, sounds like a headshop high:pac:

Deep Easterly

skipz wrote: »

I mostly think of thunderstorms as a summer time thing, surely we wont get to much action in the cooler months?

You are right, thunderstorms are more frequent* during the summer months, but thunderstorms in the Autumn/Winter time can happen. Normally, they bring nothing more than a few flashes and a couple of bangs, but very occassionally, something much more intense will pass through. Some of the most dramatic lightning strokes I have ever witnessed have occurred during the winter months.

Roll on the squalls!!!

*a strictly relative term...

Su Campu

Deep Easterly wrote: »

61-90 average number of days with thunder for each month from October to Feb at each of the long-term met eireann synoptic stations:



Data Source: Met Eireann Climate Averages & Extremes

Of course with so many of those stations now unmanned or decommissioned, it would be difficult to generate the same table for more recent periods, as there are no observers there to record the thunderstorms. :mad:

One step forward, four steps backwards.....

Storm 10

To be honest most of the best thunderstorms that I see here are in winter especially after a storm passes and the heavy squally showers move in, normally very blue lightning

Deep Easterly

Found this little video I took last July 2009 as a series of storms moved in from Galway bay in over Conammara. Only a couple of seconds long as the original was only about 3 mins long before I speeded it up. The shower at the time of filming was just west of Galway City: (apologies for appalling quality)

https://www.youtube.com/watch?v=L9qvcc_K7FA

The same showers were to really explode over the western Mayo later that afternoon:




Recorded stikes on Icelandic sferic map on the day in question:

Deep Easterly

Was reading through the met eireann monthly bulletins archive earlier on to see if there was any notably thundery spell in the autumn months.

Nothing much, but the 21st to 23rd October 2003 seemed to be one exception. Thundery showers affected the east coast, and in particular the greater Dublin region, for a period of 36hrs almost non-stop!!!

Here is how the event is described in the October 2003 monthly bulletin

"Low pressure to the southeast of Ireland between the 21st
and 23rd generated a strong north to northeasterly airstream
over the country. These very cold winds picked up moisture
as they moved over the relatively warm waters of the Irish
Sea, generating thunderstorms over the Dublin area in
particular. Between 1900 on the 21st and 0700 on the 23rd,
thunder was reported during 22 hours of the 36-hour period.

Many of the showers were of hail and with
temperatures just above freezing for part of the period, snow
also fell over higher ground. Casement Aerodrome’s fall of
51.6mm on the 22nd was the highest midnight-to-midnight fall
for October at the station since records began there in 1964".


Screen grab of rain radar from the same met eireann PDF for the morning of the 23rd of October 2003:


pretty nasty looking by all accounts!



As descibed in the met summary, the cause of this almost continous series of thunder showers in the region was the result of very unstable airmass that followed on from cold front that moved down across the country late in the evening of the 20th of Oct:



It is interesting to note that despite the passage of the trough, pressure contiuned to fall, and quite rapidly, in its wake, which is a good sign that the instability is increasing rapidly within the cool sector. Chart for the 22nd 00z shows just how much the air pressure fell behing the cold front:



showery trough developing over the relatively warm waters of the Irish sea.



Satalite pics of the event:

The evening of the 21st Oct:



showers begin to impinge on the east coast.



By the small hours of the 22nd, organised and intense showers are buffeting much of the east coast into the east midlands:





Showers continue to move in over the east on the afternoon of the 22nd:





It is not until the morning of the 23rd that the air begins to stablise:






UK Met Office recorded strikes for the month of October 2003 showing the extent of the lightning over the east from these showers:





Lets hope for a similar event this autumn!


Data sources:
Met Eireann,
UK Met Office
Dundee University.

Deep Easterly

Just using this post to add more images as attachments on the post above because we are only allowed 5 attached images per post...

Su Campu

Thanks for the post Deep, I remember that night well. Some very nice purple lightning, of which I got some video, but of course lost it when my other laptop packed it in on me! :mad:

demakinz

That lightning in 2003 i was in Intel working on the construction site and they had to raise one of the huge cranes to protect the factory. My friend and i stayed an hour after work in the car watching the crane get struck several times over and over. It was amazing.

Su Campu

I wonder if we'll see something in southeastern parts Tuesday night/Wednesday morning. Models have pretty heavy rainrates near the triple point of the frontal system as it moves eastwards across the country. At mid-upper levels the trough becomes negatively tilted, maximising lapse rates, and with decent deep layer shear present, there could be some very heavy pulses as the occulsion clears the southeast and east coast, p[ossibly giving rise to embedded thunderstorms.

Behind the system Wednesday the airmass is a lot cooler and drier, with single digit dewpoints and low level cold air advection putting a strain on deep convection, except maybe over the western half of the country, where showery troughs will probably move in off the Atlantic.

delw

remember the 2003 event very well,couldnt belive the amount of hail came down the chimmeny,black dots every were on tiles,happy days:)

Lumi

Fantastic post Patrick - thanks!!
The thunder and lightning was discussed on boards at the time
http://www.boards.ie/vbulletin/showthread.php?t=121267
but unfortunately the link to some video footage no longer works

Trogdor

Thanks for that Patrick, remember the 2003 event very well and the lack of power as things really got going dumped quite a bit of snow on the higher wicklow mountains as well iirc!

Deep Easterly

Fionagus wrote: »

Fantastic post Patrick - thanks!!
The thunder and lightning was discussed on boards
http://www.boards.ie/vbulletin/showthread.php?t=121267
but unfortunately the link to some video footage no longer works

Interesting blast from the past there! I didn't even know boards.ie existed back then!

Thought one post in particular summed up the actual specifics of the event nicely:

"It still works on the same principles, but at the moment we have really cold arctic air coming down over relatively cold seas and convecting upward really strongly.

That it lasted so long is weird, though it's more loads of seperate ones than one big one sticking around for ages".


I think he/she/it meant to say 'warm' rather than 'cold' seas though.

Min

We didn't have many thunderstorms this year, very, very few in fact, 2009 was a great summer for thunderstorms, very regular.

Kilkenny gets most of it's thunderstorms in the warmer months, I have never seen thundersnow around here but I have near Mount Leinster.

skipz

I seen a small bit of convection today with a tiny anvil at the top of one clouds, any rumbles around the country?

IMC042

Plenty of convection around cork today and some heavy showers developed. I didnt hear any thunder though but it could happen yet!

Wertz

Pretty impressive shower here (N Louth) just now, came in with the underside of the cloud lit up pink and orange by setting sun.
Heavy, looked like it had thundery potential...looks good on the radar too at 6.45...

John2009

Plenty of convection around my area today

loads of photos from earlier, i had my young fella today so my hands were full but i still managed to click a few snaps

we were out the front of the house just after midday playing abit of the 'ol hurling when i spotted something in the distant out of the corner of my eye

enjoy







it then started to kinda rope out abit and get skinny so i decided on 1 or 2 close ups, please bare in mind that i was using the fathers Panasonic Lumix TZ3 without a tripod and zoomed in fully, they probably would have turned out abit better if i had a tripod,

my little fella wanted to play trains then so that was that finished with the storm chasing for today







got some more then after a trek around the park

Su Campu

Good shots John, well spotted. You should report that on the ESWD or TORRO sites

John2009

Heres a quick clip of the funnel from earlier today, hands were a little shaky with excitement of wanting an F5 to form in front of me and whip across the countryside

sorry that the clip is in a fixed position as the Panasonic Lumix TZ3 that i used doesnt have a zoom function whilst recording video and it was during filming that i realised i should have zoomed in abit more before pressing record but you still get to see the goodies,

roll on my birthday as i'm getting the Panasonic Lumix TZ10, cracking camera

please excuse the bossman at the end of the clip wanting daddy to stop storm chasing and play trains instead

https://www.youtube.com/watch?v=xAyLJ0GFLYg

Storm 10

Lots of lightning strikes off the West Coast heading my way hopefully

http://www.laoisweather.com/index.php?option=com_content&view=article&id=48&Itemid=57&637785ce63d5d53727ddaf08c2f3f540=09bf0c9142cb1b93b004414c0cc38d4d

Su Campu

Those thundery showers that MT spoke of in his forecast are now making their way in over western Mayo and Galway, with some lightning strikes around Belmullet over the last hour or so.

With warm air advection at low levels and coldest upper temperatures off the northwest coast, these showers should continue giving heavy rain and lightning well after dark.

Hooter23

Just had heavy shower with hail in Galway defiantly feels like thunder on the way I knew it even b4 I saw the forecast:pac:

Deep Easterly

Hooter23 wrote: »

Just had heavy shower with hail in Galway defiantly feels like thunder on the way I knew it even b4 I saw the forecast:pac:

Got hit by that same shower while driving through Claregalway but was nothing special. Shower looked more impressive coming in and moving out than it actually was overhead.

Hooter23

Is there something wrong with met eireann radar as it shows Galway in a dry slot about now and we just got another shower

Deep Easterly

Hooter23 wrote: »

Is there something wrong with met eireann radar as it shows Galway in a dry slot about now and we just got another shower

This radar updates quicker

http://www.raintoday.co.uk/

shows a shower over Galway.

Hooter23

Ya I saw the shower coming in the distance it just looked a lot bigger than what was shown on radar:mad:
Thanks 4 the link D.E

rhonin

Was walking the dogs on the beach near Strandhill around 18:00 when I saw this approaching. Needless to say we rushed back to the car

Deep Easterly

Some very intense bursts of rain moving through at the moment with hail. Sporadic enough though at the moment.

Storm 10

Latest radar looks to have some pretty nasty looking rain heading our way wonder if its active ???

http://www.met.ie/latest/rainfall_radar.asp

Deep Easterly

Storm 10 wrote: »

Latest radar looks to have some pretty nasty looking rain heading our way wonder if its active ???

http://www.met.ie/latest/rainfall_radar.asp

Am watching that Storm 10, seems to be losing intensity a bit as it moves into the bay but who knows, it may pep up again as it comes onshore.

Strike off the coast of Mayo in the last half hour.

http://www.meteox.nl/h.aspx?r=&jaar=-3&soort=satradar

Storm 10

Surprising given the radar colors that we are not seeing more action from these showers, we had a very big one around 7.30 pm it was so dark and evil looking yet nothing from it just torrential rain with hail.

Deep Easterly

There is definetly signs that a little convection going on here at the moment. Rain rate has shot up to 10.1mm/ph from nothing in the last couple of minutes. :eek:

Edit, all quite again! :rolleyes:

M.T. Cranium

Western Mayo and Galway can expect several more waves of these blustery showers, one coming in now and another one visible on satellite imagery about six hours out (around 12-13 W now). Perhaps there will be more lightning with the activity tomorrow morning as freezing levels are getting lower with time.

Storm 10

Is that heading my way MT

Deep Easterly

M.T. Cranium wrote: »

Western Mayo and Galway can expect several more waves of these blustery showers, one coming in now and another one visible on satellite imagery about six hours out (around 12-13 W now). Perhaps there will be more lightning with the activity tomorrow morning as freezing levels are getting lower with time.

Thanks M.T. Hopefully something to look forward too. I think lightning is off the cards for me tonight (NE Co Galway) though as I usually associate lightning with wind at this time of year but all we have at the moment is just a 7mph mean wind speed which is backing a little to the SSW. Pressure is steady on 995.1mb

Grand total of 6.9mm today, much of which fell in some ferocious showers in the late morning. Very little rain actually fell from the main frontal zone that passed over last night which I was surprised at.

Lumi

Deep Easterly wrote: »

There is definetly signs that a little convection going on here at the moment. Rain rate has shot up to 10.1mm/ph from nothing in the last couple of minutes. :eek:

Edit, all quite again! :rolleyes:

Exactly! While the radar looks promising actual shower activity has been limited to a few intense but short-lived bursts of rain with a little hail!

Hopefully as MT suggests there may be a little more excitement on offer weather wise later

Storm 10

Very active looking one just entering Galway Bay now hopefully there may be something in it.

Deep Easterly

Latest radar grab has those showers beefing up a little over the bay alright:



Destination Tuam????? :cool:

Storm 10

Galway first you can have the left overs :D:D

Lumi

Deep Easterly wrote: »

Latest radar grab has those showers beefing up a little over the bay alright:
Destination Tuam????? :cool:

Delighted to see that optimism is alive and well in Tuam tonight