What brings good summers to Ireland
FRIDAY JUNE 05, 2015
What brings good summers to Ireland?
Let's first look at what brings undesirable summers in Ireland. It may be a season when high pressure over Denmark brings low pressure to the W of Ireland causing frontal systems to swing northwards over Ireland accompanied by belts of heavy rain with thunder, warmed because the source of the air is from the south. Sequences of depressions moving eastwards at a latitude just above Scotland with associated fronts can then bring changeable weather to Ireland. Poor summers like 1954, 1965, 1967, 1974 and 1979 can be attributed to the persistence of this pattern.
Sometimes there is a northward surge of the Azores high, often as a ridge towards England or just generally northwards, which bring winds from W or SW which can bring a dry warm and humid air in July to Ireland. West and SW coasts remain dull, misty and sometimes drizzly but more sheltered areas receive the sun and the SE can become sunny and warm. Meanwhile the far north of the country may remain in the regime of the Atlantic fronts and continue unsettled although amounts of rain may decrease.
If an anticyclone (wind systems circling clockwise) occurs to the west of Ireland with cooler air drawn over the country from the NW the country may remain cloudy and possibly cool and gloomy day after day. The SW then gets the best weather and the northern counties get chilly showers near their coasts. Such summers occurred in the 1960s, e.g.1965.
But easterly winds are the best sign. Really fine weather for Ireland only occurs if westerly wind systems break down. A high pressure system over the southern North Sea that brings hot air from the Continent over the British Isles, usually with SE winds, will lower wind speeds over Ireland and allow heat to develop. If an anticyclone positions itself so as to bring winds from the NE and SE, Ireland receives long summer days with unbroken sunshine and soaring temperatures.
Usually the northward surge of pressure extends right over the British Isles to form a high cell over or near Scotland. This draws a large mass of warmed air over Ireland from the west of Spain which becomes, for Ireland a heatwave recipe. Examples have been July 1955, June 1957 and July 1977. Prolonged sunshine will result with winds are from the NE or E of Scotland when the air source is from Scandanavia or even the Arctic with temperatures over 20C from May to mid-September. Such occurred in August 1968, June 1976 and August 1977. In Donegal some still maintain 1968 was the best summer of last century.
The reader may now care to note in passing that 1976/7 is one 18-19 year moon cycle onwards from 1959, which brought a glorious summer. It is also one moon cycle before 1995 which was equally memorable, and exactly another moon cycle before 2013, which we all fondly recall was a summer seemingly one out the bag. Accordingly before 1959 there were the good summers of 1940/41, 1921-23 and 1906. 1968 was a 9-year half cycle before 1977. To find out when the best summers will occur and why, this cycle and equal divisions of the cycle puts it all into a nutshell, and it is a pity the moon is not better recognised for its weather role.
There have also been other good summers in other years due to solar factors. June-August of 1975, 1976 and 1977 brought memorably good summer weather due to both. Very sunny NE to SE winds prevailed. The poor summers of 1978 and 1979 saw a decrease in easterly winds and a rise in the dull cooling winds from the NW. Poor summers are those where westerly patterns predominate.
Perigee is another factor. Once every 27.5-day month the moon drifts closer to earth then backs away again, called perigee by astrologers and astronomers. Perigee distance varies during the year and exactly which months have closer perigees repeats every 4-5 years. Closer perigees over the summer months also bring better summer weather. An example was 1938, when Limerick experienced 37 consecutive days with no rain.
The effect of perigee is to exaggerate the season. Whatever is about increases in intensity. Close summer perigees bring heat, close winter perigees, more cold. Close spring perigees invariably bring wind. In 2015 the closer perigees have been over February and March which has accounted for the cooler spring conditions, but close perigees are now gone until autumn. It means this summer will not be exceptional. As a comparison, in 2013 the closer perigees were in June and July. We now must wait until 2017 for closer perigees to again straddle summer months.
Our Dulux Weathershield advice in April was that after a cold and wet May (“possibly 50% more than normal”), the first half of June would bring the best of summer weather. This prediction has borne fruit, with Dublin airport receiving 50% more rain than average. And now Met Eireann is on the same page, humming happily last week that “Temperatures will rise as the run of bad weather is set to end”
The track record of our almanac is holding which bodes well for what was estimated there and in the rest of our Dulux report. June was anticipated to be the most summery month, with the second week sunny and dry, the third week wet, and then some dry days in the fourth week. The highest daytime temperatures are expected in the second week. For July you can expect rain within every three or four days, and a cloudier and cooler month than average. August has lew or no runs of dry days, but overall should be a warmer month than the average.
In summary, for this summer's driest days put a ring in your calendar around the first half of June, the third week of July and the last 4 days of July .What days to especially avoid? The wettest dates this summer may be June 16-17 and 21-23, July 1, 5-7, 12-13, 23-27 and 14-17 August
2015 Ireland Weather almanac
2015 Weather wall Calendars
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