Originally Posted by Dublin meterologist
5.3: Dublin's Most Severe Thunderstorms
5.3.1: Thunderstorm and snow, 21 November 1977 (an example of a 'winter' thunderstorm): This was the time I learnt to spell 'thunderstorm', and boy, did I never forget to afterwards. For I was terrified! It was my first experience of thunder and it happened late at night. It woke me from my sleep. I screamed and cowered under the bed sheets at every rumble of thunder as I was only 6 years old.
But God had also been good to us in a wonderful way, because the following morning came (I was almost afraid to look out the window because of the storm), IT HAD SNOWED! The thunderstorm had brought a heavy prolonged shower of snow, giving 3 or 4 inches by morning. This was an almost unheard of event for Dublin in November! I later found out that the temperature had dropped to -5C at Casement that morning. We had a day off school and lots of fun, but most of the snow had melted by the following day.
5.3.2: The Mount Merrion Thunderstorm of 11 June 1963 (a 'home-brew' thunderstorm in a south-easterly continental air mass): Reading an old copy of the Irish Times for 11 June 1963 is quite interesting. The main headline refers to the forthcoming visit of President J.F. Kennedy to Ireland, and the possibility that phone lines may be jammed during his visit (due to the FBI taking over the GPO, I presume). This is also some comment on the recent 'Profumo' affair in London. In a small corner on the front page is the day's weather forecast, reading "Another warm and sunny day, but isolated thunderstorms will break out in Munster later" or words to that effect. Not too bad a forecast for 1963....
Of course, later that day many Dubliners experienced their worst storm in living memory, when a violent thunderstorm over the Mount Merrion district deposited 184mm (7.5 inches) of rain in just a few hours, with 3.5 inches of this falling in one hour. It is quite possible that well over 200mm fell in an area where there were no rain gauges, indeed estimates of up to 235mm (9 inches) have been quoted. There was also violent thunder and lightning.
Back then I wasn't even a glint in my father's eye, for I was not born until 1971. But I have interviewed and talked to many people about that famous day (including my father), and they all have their own story to tell. It is quite remarkable that no-one was killed during the storm, for many people lost their possessions and had their homes badly flooded.
Synoptic details: A slack south-easterly airflow covered Ireland as an occluded front approached from the south-west. The previous few days had seen glorious sunshine and temperatures reaching 23-26C inland across central Ireland, although Dublin city was cooler with an onshore easterly sea-breeze, keeping temperatures at 18 or 19C.
The 11th June started similar, but by lunchtime large cumulonimbus clouds had gathered over the Mount Merrion district. These were seen clearly by golfers in Howth on the northside of Dublin, which completely escaped the storm deluge. They wondered what the fuss was all about when they got home. However, between 1 and 2pm, 85mm of rain fell at 10 Maher Road North, Mount Merrion (measured by Mr. D. Coleman). A further 100mm fell in his gauge over the following 2 to 3 hours. Rainfall isohyets indicate that the centre of the storm rainfall may have been just to the west of Mount Merrion (perhaps even over Clonskeagh), where as much as 235mm could have fallen. There are of course many accounts of the flooding - I have been told innumerable stories, of which a few include:
Rainwater raced down Goatstown hill, and backed up against a large 6 foot high granite wall at the rear of O'Briens farm. The water grew higher and higher, eventually bursting through the wall (like a damn bursting), causing water and debris to race across O'Briens front field. To this day, you can still see the huge boulder (several tonnes weight) lying in the middle of O'Briens garden (no longer a farm) left there by the massive flood.
My father remembers the little Dargle river (normally just a pathetic stream, if even flowing) flooding to perhaps 6 feet in depth, making the Goatstown Road impassable.
Prof. Gordon Herries-Davies of Trinity College told me of being unable to return home that evening due to the flood. Water was gushing down the embankment at Columnbanus (Milltown) into the river Dodder at such a rate that it looked just like a huge waterfall, several hundred yards wide. There was more water in this single outflow than in the whole river Dodder itself (which drains from Bohernabreena where between only 40 and 50mm of rain was recorded).
Mr. Douglas Gordon of Dundrum saw ball lightning bouncing along the ground in Monkstown and may actually have been hit by lightning himself!
For my undergraduate dissertation at Trinity College in 1992, I decided to measure the temperature pattern of Dublin city using mobile traverses. Some of my suspicions were confirmed when I discovered that horizontal temperature gradients of up to 8C per km can occur when certain weather situations develop. Warm residual fohn air tends to back up behind Mount Merrion hill in south-easterly airflows. The cold sea-breeze often overrides this warm air from the north-east, but usually fails. But could it have overran sufficiently on 11 June 1963 to cause massive surface layer instability over the Mount Merrion district?
Meanwhile, the Irish Times of 12 June 1963 makes even better than the day before. On the front page there are full accounts of the magnificent storm, together with photos of hundreds of buses and cars stranded at Merrion Gates, Sandymount. Unfortunately, there is no weather report - for the duty meteorologist himself was stranded by the floods and unable to come into the Irish Times office to draw the midday chart! (all weather maps were drawn by hand in those days).
An absolutely amazing and truly remarkable coincidence is that on the exact 30th anniversary of the Mount Merrion thunderstorm, that being 11 June 1993, Dublin experienced yet another massive deluge - with upwards of 110mm falling, making it the second wettest day of the century, runner-up only to 11 June 1963. I was there on that latter event, armed with my rain gauge! In a later section I have written a full account of that latter day.
W.A. Morgan, The Mount Merrion Thunderstorm, Irish Met. Service Publication (1963)
Graham, E, The Urban Heat Island of Dublin City, Irish Geography (1993)
5.3.3: The Storms of 25/26 July 1985: (This is an example of a 'home-brew' thunderstorm which formed on the boundary between humid continental air and fresher Atlantic air. The storms occurred at night and were probably caused by very rapid forced frontal uplifting). They are probably the most severe in times of lightning and continuous thunder that I have ever experienced. There were repeated cloud to ground lightning strikes throughout the night with continuous loud thunder for several hours. Up to 400 strikes per hour were later estimated to have occurred. The storm gave the impression that it would move away for 5 or 10 minutes before returning again. I was terrified (age 14) that night and prayed and prayed that the storm would just move away for good, but it didn't - it kept coming back again and again. Of course, I now realise that it was a series of different storms moving north-east along a trailing cold front and it was not the same storm repeatedly returning.
At about 5am, as the last of the cells moved away, I was brave enough to peek out the window. I saw a blaze of red and orange shimmering lights across the city, from what I presumed to be hundreds of fires caused by the lightning. The 6 o'clock news the following evening reported these storms as being the worst for 50 years (in terms of lightning and thunder). Charlie Bird showed a report from county Kildare where there were thousands of crows killed by large hailstones. Many of the hailstones were still lying in ditches on the side of the road.
5.3.4: 27 to 30 June 1986 (These storms formed in similar circumstances to the storms of 25/26 July 1985): After the storms of the previous July, we thought we had had our share and we would be spared from further violence for another 50 years. That was not to be the case, as an unusual airflow at the end of June 1986 brought several days of violent thunderstorms to be Dublin region. Although none of the storms were individually as severe as the overnight storm of 25/26 July of the previous year, it was the 4 or more continuous days of thunder that was the most surprising. Local downpours of up to 3 inches (75mm) accompanied the storms. Two lightning bolts hit within 100 metres of my parent's house on Laburnum Road, Clonskeagh. I also discovered that the shetland pony in the field beside us was hit and probably killed by lightning. During one of the evenings, another thunderstorm (but with no rain) was coincidental with a concert given by 'Simple Minds' at Croke Park in Dublin. At Clonskeagh, there was an amazing combination of distant loud music mixed with occasional thunder. It was also the same evening of the first Dublin-Belfast Co-operation-North maracycle.
5.3.5: 24 August 1990 (another 'home-brew' storm formed on the boundary between humid and fresher airmasses) : This was a much shorter storm compared to the examples above, lasting no more than one hour or so. It occurred at about 6:00pm on the day in question, which was at the end of a long and humid spell. I was just finishing my job at 'Spar' supermarket in Milltown that evening, but I was unable to leave for home at 6:00pm due to torrential rain and the fairly frequent thunder. After about 20 minutes waiting, I made a dash for it on my bicycle down Milltown hill. What I noticed then surprised me, for at the bottom of Milltown hill, only 100 metres or so away from where I had been waiting for 20 minutes, it was completely dry! The only evidence of water was from were the torrents of runoff flowing from the top of Milltown hill where I had been delayed! When I got home to Laburnum Road at about 6:30pm, my parents wondered what had delayed me - they did not believe I had to spend 20 minutes sheltering from the rain, for it was bone dry in Clonskeagh also. Eventually however, the rain started to pour down in Laburnum Road also, giving about 18mm in less than an hour.