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Convective/Thunderstorm Discussion : Spring/Summer 2020

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Just starting new thread for the season(s). Nothing to report!

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Oscar Bravo

Some sparks along that intense rain band from Dundalk to Letterkenny

Scrabbel

Hi,
A question for the very helpful experts who post on this board (your knowledge-sharing is really appreciated).

For those of us who don't have much sense of how CAPE, shear and other things like that interact and affect the likelihood of thunderstorms, is there a reasonably reliable overall measure of thunderstorm probability (and charts showing it) that we can jump straight to?

I see one measure called KO index for some models on Meteologix that sounds like it might be something along these lines. Is that a good composite measure or are there better ones that we can see on these sites?

Would appreciate any guidance. Thanks

igCorcaigh

I'd like to know too!

Are these measures of buoyancy? The upward push of rising air?

Scrabbel wrote: »

Hi,
A question for the very helpful experts who post on this board (your knowledge-sharing is really appreciated).

For those of us who don't have much sense of how CAPE, shear and other things like that interact and affect the likelihood of thunderstorms, is there a reasonably reliable overall measure of thunderstorm probability (and charts showing it) that we can jump straight to?

I see one measure called KO index for some models on Meteologix that sounds like it might be something along these lines. Is that a good composite measure or are there better ones that we can see on these sites?

Would appreciate any guidance. Thanks

highdef

highdef wrote: »

Did a few quick timelapses showing the convection in North kildare. Might have caught a brief funnel at about 17 seconds.

Fixed my timelapse link. There was an issue with it, also HD now

Meteorite58

Big convective showers but no sparks here in Kerry, less showers in the afternoon although one going through now, sunshine breaking through at least, breezy. A few sparks now near Rathcormac Co Cork. Looks like a rough day in Northern counties.

6.2mm

4rv8i9J.png?1

spookwoman

Some rumbles in waterford with heavy showers

vikings2012

Thunder and heavy rain in east Waterford at present

Teemarie

Rumbles of thunder and downpours now south wexford.

Gaoth Laidir

Scrabbel wrote: »

Hi,
A question for the very helpful experts who post on this board (your knowledge-sharing is really appreciated).

For those of us who don't have much sense of how CAPE, shear and other things like that interact and affect the likelihood of thunderstorms, is there a reasonably reliable overall measure of thunderstorm probability (and charts showing it) that we can jump straight to?

I see one measure called KO index for some models on Meteologix that sounds like it might be something along these lines. Is that a good composite measure or are there better ones that we can see on these sites?

Would appreciate any guidance. Thanks

The KO index is fairly good in warm and muggy situations like last Thursday where convective instability was present (we needed someting to lift the air to get convection started). It takes into account the difference in temperature and moisture between low and mid levels. A KO value of <2 means thunderstorms are likely, as long as there is some lifting mechanism present (from an upper shortwave and/or uplift over terrain/convergence). The sounding from that Wicklow storm below shows a KO Index of 0 (box on the right), which tallies with what happened.

CAPE is the first thing to look at, though. If there is no CAPE then that's it. If there is CAPE then it must be released, which is what didn't happen Thursday afternoon because there was too much of a cap (warm layer of air 1-2 km up) that stopped surface air parcels from rising high enough (to the level of free convection). If the CAPE is released then the Lifted Index (LI) is the next thing to look at as it tells us how many degrees warmer the rising air parcel is than its surrounding air at the 500-hPa level, however this only relates to surface-based convection. A similar index for eleveated convection is the Showalter Index, which is like the LI but for a parcel raised from the 850-hPa level, not the surface. In the sounding above the SI is about -3. A value of -4 or less means severe thunderstorms.

The other indices in that sounding are the Vertical Totals (VT) and Total Totals (TT). The VT is just the difference in temperature between 850 and 500 hPa (the higher the better) and the TT is the VT plus the the difference between the 850-hPa dewpoint and the 500-hPa temperature. A value of >50 means severe thunderstorms are possible and >56 means severe storms with tornadoes.

The EUMeTrain website is an excellent learning tool for lots of different situations. This page describes some of these indices in more detail.

Oneiric 3

Gaoth Laidir wrote: »

The KO index is fairly good in warm and muggy situations like last Thursday where convective instability was present (we needed someting to lift the air to get convection started). It takes into account the difference in temperature and moisture between low and mid levels. A KO value of <2 means thunderstorms are likely, as long as there is some lifting mechanism present (from an upper shortwave and/or uplift over terrain/convergence). The sounding from that Wicklow storm below shows a KO Index of 0 (box on the right), which tallies with what happened.

CAPE is the first thing to look at, though. If there is no CAPE then that's it. If there is CAPE then it must be released, which is what didn't happen Thursday afternoon because there was too much of a cap (warm layer of air 1-2 km up) that stopped surface air parcels from rising high enough (to the level of free convection). If the CAPE is released then the Lifted Index (LI) is the next thing to look at as it tells us how many degrees warmer the rising air parcel is than its surrounding air at the 500-hPa level, however this only relates to surface-based convection. A similar index for eleveated convection is the Showalter Index, which is like the LI but for a parcel raised from the 850-hPa level, not the surface. In the sounding above the SI is about -3. A value of -4 or less means severe thunderstorms.

The other indices in that sounding are the Vertical Totals (VT) and Total Totals (TT). The VT is just the difference in temperature between 850 and 500 hPa (the higher the better) and the TT is the VT plus the the difference between the 850-hPa dewpoint and the 500-hPa temperature. A value of >50 means severe thunderstorms are possible and >56 means severe storms with tornadoes.

The EUMeTrain website is an excellent learning tool for lots of different situations. This page describes some of these indices in more detail.

This post should be given its own thread and pinned to the top of the main page. Informative posts like this, not to mention the work put into it, are too easily lost forever in dynamic threads like this.

Scrabbel

Oneiric 3 wrote: »

This post should be given its own thread and pinned to the top of the main page. Informative posts like this, not to mention the work put into it, are too easily lost forever in dynamic threads like this.

Couldn’t agree more. Thanks so much to Gaoth Laidir. It’s exactly why it’s so good for punters to be able to tap into all the combined knowledge of the real experts on this board. A lot to get to grips with but I can already understand a bit more of what I saw in the build/up to last week.

Gaith Laidir, I’ll go to that website and read a bit more on all this. Thanks again.

Meteorite58

Small chance of some thunderstorms in south Munster, more so along coastal areas and Coastal Cork I would think has the highest chance as convection matures and reaches an area of convergence . Low chance and short lived if they do happen I reckon in the afternoon.

pad199207

Lightning in Carlow and N Wexford

CirrusBusiness

Thunder and torrential rain - Carlow/Wexford border. Very angry looking sky to the S/E. Wonder if we'll see some sparks.

Ballylad

CirrusBusiness wrote: »

Thunder and torrential rain - Carlow/Wexford border. Very angry looking sky to the S/E. Wonder if we'll see some sparks.

Yes looking towards mount Leinster from Ardattin near tullow , it looks impressive

Mortelaro

My view of that thunderstorm looking towards Gorey

https://twitter.com/Arklowweather/status/1278405631523897346?s=19

Gaoth Laidir

Looking at radar I would expect a few sparks in the south Dublin area soon too.

Larbre34

Gaoth Laidir wrote: »

Looking at radar I would expect a few sparks in the south Dublin area soon too.

I disagree, not a lot to suggest embedded activity

vickers209

Seen these on fbook apparently taken near Ballycanew co wexford this evening

vickers209

2nd shot

Bsal

Impressive looking if it's real.

Cantona's Collars

AFAIK it was near Ballycarney and there was another near Monageer.

pauldry

Just wondering is there anywhere to get the rainfall figures from last Fridays intense Thunderstorm in Sligo and Leitrim?

Markree has 5mm so they didnt get it but Sligo had 39mm as did Leitrim and North Mayo hence landslides.in Drumkeerin.

Yet Finner and Markree dont have much rain from it.

Where do I get accurate data for places that were hit?

Danno

pauldry wrote: »

Just wondering is there anywhere to get the rainfall figures from last Fridays intense Thunderstorm in Sligo and Leitrim?

Markree has 5mm so they didnt get it but Sligo had 39mm as did Leitrim and North Mayo hence landslides.in Drumkeerin.

Yet Finner and Markree dont have much rain from it.

Where do I get accurate data for places that were hit?

Try Sligo Airport data here: https://wow.met.ie/stations/20200703ceskwip7fae6ix3byyb96spgyy

Click on Data Display to set your parameters.

Friday June 26th - 18mm
Saturday June 27th - 25mm
Sunday June 28th - 32mm
Monday June 29th - 12mm

That is 87mm over a long weekend! :eek:

Also of interest there:

14/06/2020 15:30 17.3 7 See details
14/06/2020 16:00 16.0 24 See details

Went from 7mm to 24mm in half an hour!

pauldry

Thanks Danno

Closer to what we got thanks.

Still Sligo Town got 39mm Friday morning and airport is 5 or 6 miles away so we must have been in the eye.

Mortelaro

Danno wrote: »

Try Sligo Airport data here: https://wow.met.ie/stations/20200703ceskwip7fae6ix3byyb96spgyy

Click on Data Display to set your parameters.

Friday June 26th - 18mm
Saturday June 27th - 25mm
Sunday June 28th - 32mm
Monday June 29th - 12mm

That is 87mm over a long weekend! :eek:

Also of interest there:

Went from 7mm to 24mm in half an hour!

The one over Arklow that night (Friday into Saturday morning) gave me 13mm in 40 mins between 3am and 340am approx
The water from it cut a track down a lane into the yard here

pauldry

Mortelaro wrote: »

The one over Arklow that night (Friday into Saturday morning) gave me 13mm in 40 mins between 3am and 340am approx
The water from it cut a track down a lane into the yard here

Same as

The track at cleveragh park washed down onto the main path below

Meteorite58

From Convective Weather

https://twitter.com/convectivewx/status/1278755286812168194?s=20

That hot spot looks around Thurles / Cashel or thereabouts ?

Near Sligo features well.

Kermit.de.frog

I luv storms

M.T. Cranium

Things are now looking quite active for the late overnight and Sunday morning time frame, unstable westerly flow with embedded troughs will be the scenario, possible fast moving squally showers or thunderstorms, small hail, local wind damage, under a strong jet stream that looks like it got lost on the way to October or November.