A sub classification of the classic spanish plume?

[Josh Cool Stundon]

Hello all. 

 

So I am aware that there are at least 3 spanish plume regimes that lead to severe thunderstorms in the UK, ireland and northwest Europe. The classical spanish plume, the modified spanish plume, and the european easterly plume. However, I am wondering if perhaps there could be a sub classification of the classic spanish plume? 

 

For instance, the classical spanish plume often leads to severe thunderstorms that are typically confined to southeast England, and not effecting Ireland, or the north and west of the UK. Yet it seems that in rare cases, the classic spanish plume has lead to severe thunderstorms much further north and west. June 28th 2012 is one such example. I also recall the severe thunderstorms of August 31 2005 as another example. 

 

Of spesific interest to me were a few things mentioned in the estofex convective outlook for that day. ““models show deepening low pressure system moving from northern bay of biscay to southeastern Ireland”. 

 

A surface cold front moved across Ireland on that day, and a wave formed along the front over westcentral Ireland around midday, which is probably what lead to the severe thunderstorms in the Limerick area which is where I live. 

 

A very similar situation took place on July 25-26 1985. This situation lead to one of irelands most violent thunderstorm events on record. 

[Metwatch]

 

@Josh Cool Stundon Not sure about sub classifications of Spanish Plumes but this paper might be of interest relating to various weather patterns and which produce thunderstorms in the 2010s, at least for the UK.

There is a brief discussion on plumes though:

weather patterns and observed lightning UK.pdf

Edited April 20 by Metwatch

[Josh Cool Stundon]

Hello, thanks for your reply. Unfortunately, I was not able to read much of the article because I am visually impaired and a lot of pdfs wont read with my screen reader. Are you able to copy and paste what the article says about plume setups?

[MP-R]

Plume storms that end up just skimming the southeast tend to be the ones that go wrong or are ‘cut short’ by the westerly influence shunting things along too quickly.

The classics tend to affect the SW and/or the S Central region first before advancing north and east.

[Cambrian]

@Josh Cool Stundon

Hi Josh,

I think that we have to look at each event on its own rather than necessarily seeking a sub-classification of the classic Spanish plume. 

I have looked at the archive charts for June 28th 2012. What is striking about that event is the dramatic west-east temperature gradient that developed that day and how the contrasting air masses interacted in the circulation of the developing low pressure system. I have examined the pressure charts and the T850 charts, relevant here because the 850 hPa temperature, at altitude about 1.5 km, is above the atmospheric boundary layer and so is a very good measure of the relative temperatures of the air masses.

At 0z that day, the low pressure at around 1000mb, was centred about 800 km to the southwest of Ireland. The pressure was around 1005mb over southwest Ireland. The T850 was around 11 degrees over Limerick and around 14 degrees over southeast England, though the 16 degree isotherm of the plume was over the English Channel coast. The surface circulation over Ireland was a southeasterly, drawing in warm, humid air from that region. 

By 6z, the low pressure had extended northeast, and the pressure over southwest Ireland had fallen to 1000mb. The centre of the low was by then around 400 km to the west of Kerry. The T850 over Limerick was around 9 degrees, and the 16 degree isotherm had arrived in southeast England. The surface flow into southwest Ireland was still from the southeast, continuing to feed in warm, humid and unstable air. 

By 12z, the deepening of the low pressure, to around 995mb had pulled in colder air from the northwest, so that the T850 over Kerry and West Cork was only 6 degrees and this knuckle of much cooler air was pushing in from the southwest behind a developing front, into the very warm humid air to the east of it. The T850 over Kent was around 17 degrees, so two things had happened.

Firstly, over 12 hours, the difference in T850 between southwest Ireland and southeast England had risen from 3 degrees to an 11 degree difference, so the temperature gradient had become extremely steep. The atmospheric instability through that zone would have become profound. 

Secondly, the centre of the approaching low pressure had more or less stalled, still several hundred kilometres to the southwest of Ireland but the low was deepening in situ, so all of Ireland was by then below 1000mb as the system grew. The winds would have been slight and variable within this cyclonic circulation but with the dramatic west-east temperature contrasts within the system, and the peak convection of the afternoon, severe thunderstorms would have formed through the frontal zone, fed by the growing instability and making only very slow eastward progress. As the front approached, the wind would have backed southerly running along the front, so a local effect of air getting lifted over the Cork and Kerry mountains, enhancing the updrafts, might have been an additional factor for the Limerick area.

Limerick was in effect stuck in the trigger zone for several hours with the growing temperature contrast of the air masses and increasing convection of the day feeding a growing instability that resulted in the severe thunderstorms. 

I hope this helps look at the question in another way. The precise setup for each instance of this type of event is naturally different, but I was hoping that by looking at the dynamics of this particular event, the requisites might be identified. 

Edited April 21 by Cambrian

[Metwatch]

12 hours ago, Josh Cool Stundon said:

Are you able to copy and paste what the article says about plume setups?

Of course! Hope this helps:

Quote

 

"Finally, in the summer (Figure 6f), there are three PTWPs which occur slightly less frequently than normal (16, 21 and 22) and three which occur slightly more frequently (5, 8 and 11). Of the “less frequent” weather patterns, two of these (16 and 22) are worthy of further discussion. Examining Figure 2, it can be seen that both these weather patterns exhibit a low-pressure system to the west of the study domain and high pressure to the east of the study domain, with warmer air being advected from continental Europe. In Figure 2, we see that in weather pattern 22, the high pressure is further to the east and the low pressure further north and east than in weather pattern 16. Both weather patterns have flow over the domain coming from continental Europe. Strong southerly flow with air from Iberia coupled with a low-pressure system to the west of Ireland are notable features of the “Spanish Plume,” identified by Morris (1986). This is believed to be the predominant mechanism which leads to thunderstorms in the summertime over Britain and Ireland and occurs when warm and moist air flows northwards from Iberia, leading to an unstable environment favourable for thunderstorm development. The Spanish Plume has also been connected to severe storms in other parts of Europe (e.g., Van Delden, 2001; Piper and Kunz, 2017).

However, it is difficult to define a Spanish Plume by pressure patterns alone. For example, Sibley (2012) discusses a Spanish Plume case on June 28, 2011. Using the ERA5 weather patterns set described in Section 2, this case can be diagnosed as weather pattern 6 (Azores high extension over UK). In this specific case, the pressure gradient was weaker than the mean pressure shown in weather patterns 16 and 22, even though the flow was from Iberia. Analysing mesoscale convective systems over the UK, Lewis and Gray (2010) note two types of Spanish Plume, a “classic” and a “modified,” with different baroclinic life cycles. Their classic Spanish Plume model has warm moist air from Iberia capped by warmer but very dry air from the Spanish plateau; this is associated with a baroclinic wave on a developing low-pressure system. The modified Spanish plume consists of a more mature system with a forward tilted trough. Given that the low-pressure systems to the west of the domain of study in weather patterns 16 and 22 appear mature, these patterns are probably more representative of the modified Spanish Plume from the Lewis and Gray (2010) study. Given that Spanish plumes may fall into more than one surface pressure pattern, for the remainder of the manuscript, weather patterns 16 and 22 will simply be described as weather patterns with a strong southerly flow (SSF)"

 

 

11 hours ago, MP-R said:

Plume storms that end up just skimming the southeast tend to be the ones that go wrong or are ‘cut short’ by the westerly influence shunting things along too quickly.

There was a few instances last year, where one case 19th August that just clipped the south east. The second instance 24th August, had quite a westerly motion to the storms compared to the 19th, but only clipped the south coast. 2nd October was similar to the 24th august in some ways with a mostly westerly influence rather than southerly or southwesterly, but was a bit more widespread interestingly, likely the destabilition and airmass clash occuring further north.

[MP-R]

 Metwatch Interestingly, that 02nd October chart looks like a standard rPm cyclonic setup  Wouldn't even be able to tell it was a plume looking at that.

[Josh Cool Stundon]

@cambrian very interesting reply! What about the charts for August 31 2005? Limerick had some of the strongest thunderstorms I had experienced in a long time on that day in many years. 

[Metwatch]

3 hours ago, Josh Cool Stundon said:

What about the charts for August 31 2005? Limerick had some of the strongest thunderstorms I had experienced in a long time on that day in many years. 

Wetterzentrale has a collection of charts going back to the 19th century: https://www.wetterzentrale.de/reanalysis.php?jaar=2005&maand=8&dag=31&uur=1800&var=1&map=1&model=cfsr

Though looking at 31st August 2005 can see why it would have caused some potent thunderstorms. A strengthening cut-off low pressure system from the Azores moved northeastwards bringing with it, a very warm, humid and so an increasingly unstable airmass from Spain and the Bay of Biscay.

Doesn't seem to be any articles or write-ups about that specific event unfortunately, which is also the case with several other weather events in more recent years that have still led to impacts.

Edited April 21 by Metwatch

[Josh Cool Stundon]

I have noticed that alright. The only write up I could find about August 31 2005 was a few sentences written in the British isles weather diary for 2005. I think a cold front moved across Ireland and western Scotland? Unfortunately, my screen reader doesn’t read charts or graphical information. But it is disappointing that there are no articles written about this particular event. It was really quite outstanding in the Limerick area and I had rarely experienced anything like it since.