Convective/Thunderstorm Discussion : Spring/Summer 2020

Gaoth Laidir · 27-06-2020 6:20pm

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 · 27-06-2020 9:03pm

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 · 28-06-2020 10:43am

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 · 01-07-2020 9:55am

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 · 01-07-2020 7:21pm

Lightning in Carlow and N Wexford

CirrusBusiness · 01-07-2020 7:32pm

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

Ballylad · 01-07-2020 7:44pm

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 · 01-07-2020 8:11pm

My view of that thunderstorm looking towards Gorey

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

Gaoth Laidir · 01-07-2020 8:43pm

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

Larbre34 · 01-07-2020 9:00pm

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 · 02-07-2020 12:18am

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

vickers209 · 02-07-2020 12:21am

2nd shot

Bsal · 02-07-2020 12:52am

Impressive looking if it's real.

Cantona's Collars · 02-07-2020 12:53am

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

pauldry · 03-07-2020 1:48pm

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 · 03-07-2020 2:58pm

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 · 03-07-2020 3:24pm

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 · 03-07-2020 3:28pm

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 · 03-07-2020 4:07pm

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 · 03-07-2020 7:54pm

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 · 03-07-2020 8:02pm

I luv storms

M.T. Cranium · 04-07-2020 7:15am

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.

First Up · 04-07-2020 7:17am

M.T. Cranium wrote:

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.

Any parts of the country at most risk?

Donegal Storm · 04-07-2020 11:03am

Meteorite58 wrote: »

That hot spot looks around Thurles / Cashel or thereabouts ?

Near Sligo features well.

I'd assume that spot is some sort of error? Hard to believe one random non-descript spot in Tipperary is by far the most thundery place in the country!

Also locally I think I've only experienced thunder/lightning once this year so the Donegal colours seem a bit generous

pauldry · 04-07-2020 11:04am

The West and Northwest look like bearing the brunt of this with 120kph gusts possible in Finner or Sligo airport

Meteorite58 · 04-07-2020 11:28am

Donegal Storm wrote: »

I'd assume that spot is some sort of error? Hard to believe one random non-descript spot in Tipperary is by far the most thundery place in the country!

Also locally I think I've only experienced thunder/lightning once this year so the Donegal colours seem a bit generous

Must look into it further when I have time .

Gonzo · 04-07-2020 11:30am

that thunder chart is certainly right for my area, south-east Meath with a grey colour showing 0 days of thunder and lightning.

Gaoth Laidir · 04-07-2020 12:10pm

What isn't an error is that blank spot through NE Kildare. Have seen f all here this year.

Oneiric 3 · 04-07-2020 4:43pm

Donegal Storm wrote: »

I'd assume that spot is some sort of error? Hard to believe one random non-descript spot in Tipperary is by far the most thundery place in the country!

Also locally I think I've only experienced thunder/lightning once this year so the Donegal colours seem a bit generous

Seems about right for here, underplaying it if anything as we had a fair amount of days with thunder observed during the first quart of the year.

Mortelaro · 04-07-2020 4:52pm

Gonzo wrote: »

that thunder chart is certainly right for my area, south-east Meath with a grey colour showing 0 days of thunder and lightning.

its wrong for parts of East wicklow anyway as all of east wicklow had last weekends storms
Here in SE Wicklow I've had 3, I think

Oneiric 3 · 04-07-2020 5:23pm

Mortelaro wrote: »

its wrong for parts of East wicklow anyway as all of east wicklow had last weekends storms
Here in SE Wicklow I've had 3, I think

Seems the map is based on Sferic data, which is at best crap and at worst, downright misleading as it only picks up a fraction of lightning occurrences in reality with a bias toward cloud to ground.

M.T. Cranium · 04-07-2020 5:39pm

As to potential overnight and Sunday, would say all regions have potential since the prime generator will be unstable troughs embedded in fast westerly flow. At a guess, the Galway to Dublin corridor perhaps more favoured than other areas but differential may be slight. There seems to have been a downgrade as far as met service are concerned but I was surprised to see that after first checking the latest obs since those had come in about as expected.

In any case, this would likely become a nowcasting challenge through the period especially Sunday morning, so stay tuned, radar watching commences shortly.

SlowBlowin · 04-07-2020 8:17pm

Gusts here 20 minutes ago, Sneem area without power.

PukkaStukka · 05-07-2020 11:04am

Several sferics reported over the Irish sea this morning. Squally morning with convection about

SlowBlowin · 17-07-2020 10:37pm

Met.ie showing potential thunderstorm activity in west Kerry at 6 am tomorrow.

Any further info on the likelihood of this occurring ?

Danno · 18-07-2020 12:32am

SlowBlowin wrote: »

Met.ie showing potential thunderstorm activity in west Kerry at 6 am tomorrow.

Any further info on the likelihood of this occurring ?

I would be surprised if this were to materialise. Thunderstorm activity in a relatively flat-line west-to-east flow at this time of year is quite rare.

SlowBlowin · 18-07-2020 5:05am

Danno wrote: »

I would be surprised if this were to materialise. Thunderstorm activity in a relatively flat-line west-to-east flow at this time of year is quite rare.

Met.ie now showing thunderstorms at 8 am.

repulsebay321 · 18-07-2020 8:02am

Heavy downpours in Cork in the last hour.

Meteorite58 · 22-07-2020 11:42pm

Fri ( low chance in the W ), early Sat morning ( passage of an unstable trough ) and Sat some chance of thunderstorms, more so Saturday from the afternoon. Charts showing cold uppers spread over the country on Saturday, decent shear and lapse rates coinciding with peak diurnal heating possible. Heavy showers, some of hail maybe. Would think the Eastern half of the country with best chance of thunderstorms as convection matures as it crosses the country from W to E. Some nice convergence near the S and E coasts.

Meteorite58 · 23-07-2020 11:53pm

An interesting day Saturday perhaps during the passage of an unstable trough producing heavy showers and giving thunderstorm potential.

Meteorite58 · 24-07-2020 10:59am

Hi Res AROME looking good for some thunderstorms tomorrow.

Meteorite58 · 24-07-2020 8:57pm

S, SE and E look like getting the heaviest rain tomorrow afternoon as convection matures crossing the country into the evening ( parts of the Midlands and N could see heavy rain also ), a bit of spot flooding in a few places perhaps.

DP's 12 to 14C in general .

Thinking that it might be possible to get warnings perhaps if thunderstorms materialize to some extent in the afternoon as they progress across the country .