Rainfall record at Casement Aerodrome

A total of 82mms of rain (more than three inches) fell yesterday at Casement Aerodrome, one of Dublin’s main weather stations.

The rainfall is an October record and an event likely to occur only once every 20 years.

Much of the torrential downpours were concentrated in a six hour spell yesterday afternoon between 2pm and 8pm when a phenomenal 65.7mms of rain fell. That is a once in 80 year event, according to Met Éireann.

The 23mms (almost an inch) of rain that fell between 4pm and 5pm was the greatest amount of rainfall ever recorded at Casement Aerodrome since records began in 1954.

The stations at Dublin Airport and the Phoenix Park also had significant daily rainfall totals of 69.1mm and 71.3mm respectively. These too are rainfall events only likely to occur every 20 to 25 years.

Though the rainfall yesterday was bad, it was not a record for Dublin. Over 180mm was recorded on 11th June 1963 during a violent thunderstorm in the Mount Merrion area of South Dublin. Exactly 30 years later on June 11th 1993 more than 100mms of rain fell in a 24 hour period in the Dublin area.

The heaviest rainfall yesterday was nearly all concentrated in the Dublin and Wicklow areas. Johnstown Castle in Co Wexford recorded 22.4mms of rain and Dunsany in Co Meath 37.8mms.

Met Éireann forecaster David Rogers said a combination of factors caused more than a month’s worth of rainfall to fall in a short time period in Dublin.

He said Ireland was at the centre of a slow-moving frontal depression which stretched from western France to south of Iceland.

The Wicklow Mountains caused a process called orographic uplift when moist air is forced to rise by a mountain barrier, condenses and then falls as rain. In addition, there was coastal convergence or the convergence of isobars, indicating atmospheric pressure, off the east coast which also caused moist air to rise and fall as rain.

“The whole lot conspired to produce excessive rainfall. It is not the first or last time this happened,” he said.

The forecast is for brighter and drier conditions in the following days.

Tomorrow and Thursday will see outbreaks of drizzle. Temperatures will be between 9 and 12 degrees falling to a cold 3 and 6 degrees at night.

Rain will push in from the west on Friday and it will feel cool with fresh southerly winds.

The forecast on Saturday and Sunday is for some wind and rain, but nothing out of the ordinary for this time of year.