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50 Years ago today

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  • 11-06-2013 9:59pm
    #1
    Registered Users Posts: 10,758 ✭✭✭✭


    The Mount Merrian thunderstorm took place on the 11th of June 1963.
    There's a piece on MET Éireann about it.
    Any boardsies here remember it?

    Today, 11th June 2013, marks the 50th anniversary of one of the most violent thunderstorms to affect Dublin in the 20th century. On the 11th June 1963 considerable flooding occurred in the area between Dundrum, Blackrock and Sandymount. The “official” observations only hinted at the full severity of the rainfall. Eye-witness accounts suggested that far more than the 97.8mm (24-hour total) recorded at Ballsbridge fell in some locations. Following a public appeal for additional information several individuals came forward with amateur observations based on the rainfall collected in garden buckets during the storm. While it was impossible to verify the accuracy of these measurements (and the exposure of the sites would not have been meteorologically acceptable) the general consistency of the data within the area suggested that local rainfall totals probably exceeded 150mm. The intensity of the rainfall was also remarkable: at Mount Merrion at least 75mm of rain fell in one hour.
    Copy_Flooding-June-1963.jpgAnd the forecast for that day? According to the Irish Times, the forecast issued on the 10th June 1963 suggested "mainly fair or fine" with "scattered outbreaks of thundery rain in Munster and South Leinster". Given that there were no computer forecast models available at the time (and no radar or satellite data), the forecast was not wildly inaccurate but it did fail to warn of exceptional rainfall.
    Would we do better today? Met Éireann research staff re-ran the forecast for 11th June 1963 using its current operational high-resolution weather model (called Harmonie). The Harmonie forecast suggested a total of about 30mm of rainfall over the Dublin area but in other parts of the country the totals exceeded about 90mm. Given the random nature of thundery showers it is not too surprising that the exact details were not captured. Even higher resolution models (Harmonie currently runs on a 2.5km grid) might give a better deterministic forecast but running many forecasts - an ensemble of forecasts - from slightly differing initial states might be a better strategy to address the randomness of these events.
    If this forecast had been available 50 years ago, the forecaster might have emphasised the risks of torrential downpours in thundery showers. Today, such a forecast would lead to a weather alert for the Local Authorities regarding the possibility of significant local flooding. Also, today we have radar and satellite imagery to track the development of intense weather features, enabling Met Éireann to rapidly update forecasts.
    The following footage, supplied by Helen Carroll, shows the flooding at Dundrum and Roebuck Road in June 1963.


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