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May weather

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One expects May to be a month of pleasant weather and gentle temperatures, but in fact it can be a very mixed month, with quite substantial fluctuations.

The month ought to be like 2001 or 2011, when May was largely sunny, but more often than not it sees quite a bit of drab, grey conditions. A mixture of high and low pressure often brings these conditions. Lows obviously bring cloud and cooler conditions, but highs do not always result in sunshine either. Much depends on where the high is situated and whether it brings in air from the warmer south and west or cooler east and north.

With the sea still cold, any airflow coming over the sea also tends to create cool grey cloud, often bubbling up after sunny starts and then clearing at dusk. May also seems to have a propensity towards static or slow-moving lows, which bring cool, showery weather, though interspersed with some sunny days.

From cold to hot and back again

2010 provided an excellent example of both types of high pressure. In the first half of the month highs to the west and northwest of the UK brought cool winds from the north and north east, with temperatures of just 11-12 degrees by day and low single figures at night. Many days in this period turned cloudy after a sunny start. But then from 15 to 25 May, high pressure to the south of the UK brought air up from the Azores and created a heatwave, with plenty of blue skies and temperatures getting as high as 27 degrees. Only in the last six days of the months did Atlantic lows break through, producing cooler, wetter conditions.

2002, 2004 and 2017 saw similar patterns. In 2002 high pressure kept the first three weeks of the month grey and cloudy before sun broke through in the last week, and in 2004 it was the first 12 days which were cloudy, with the rest of the month seeing blazing sunshine. In 2017 the month started with high pressure to the north, producing an easterly wind of the North Sea. Then from the 11th onwards static lows dominated till the 21st. This meant that the first three weeks were fairly cloudy, though with relatively little rain apart from the 18th and 19th. But then from the 22nd onwards a continental high brought a heatwave, with hot sunshine and temperatures up to 28 degrees

In 2008 the order was reversed, with highs bringing wonderful sunny weather till mid month, with temperatures in the low 20s, and then cooler and wetter (though still fairly static) weather setting in the second half. 2013 saw a sunny first and fourth week, with cloudy slow moving lows in between. Temperatures under the cloud were as low as 11 degrees, dipping to 9 degrees on the 24th when the wind turned northerly.

In 2009, the weather alternated every few days between between lows to the north (some fairly static, and bringing quite strong winds to the south) and periods of high pressure: the latter produced four periods of sunshine, with temperatures rising from 18-21 degrees mid month to 25-27 degrees towards the end.

2014 also saw highs and lows alternating, with a sunny early May bank holiday weekend being followed by eight cool and showery days. From the 13th to the 19th high pressure then brought increasing sunshine, with temperatures building to 26 degrees, before static lows (caused by a blocking high over Russia) brought cool and showery weather for the rest of the month.

May 2016 was another month of alternating highs and lows, but saw good amounts of blue sky (twelve sunny days, six of sun and cloud), with cloudier, wetter periods from 10-11, 17-22 and 29-31 May. Temperatures were in the high teens, with a brief foray into the mid twenties on 6-9 May - a welcome change to the end of April, when there had been a week of wintry north winds with highs of only 9 degrees. Towards the end of the month a static low set in over the near continent that was to bring cool cloud to the south east in early June while Scotland basked in hot sunshine.

In 2011 a hot drought that had lasted since late March and brought summer temperatures finally ended on 7 May with heavy downpours. The month then reverted to sunshine, however, with a mixture of static highs and lows. These produced much cooler and breezier conditions than in April, with temperatures mainly in the high teens, but there were only isolated and light showers for much of the month. Then just when the drought seemed to be setting in for the summer, there was substantial rain across the south east on the 26th, and more on the 30th and 31st, with the month ending on a cool, grey note.

In 2005 high pressure drove icy cold winds down the east coast in the second and third week, even producing night time frosts. In the fourth week, it then gave way to a slow moving low which was bad news for the north, which had lots of wet weather, but generally good for the south, bringing scudding clouds and sunny intervals.

Years when May was wet

More unusually, May can be dominated by Atlantic lows, as happened in 2006, 2007, 2012 and 2015. 2006 was the wettest May for 23 years, and 2007 was relentlessly grey, showery and cool - a big surprise following a hot and sunny April (it was on 7 May that the drought finally broke). In both years there were days right up to the end of the month when one felt like running the central heating.

That was also true in the first three weeks of May 2012, when - continuing a wet theme established in April - the weather remained stubbornly cold and wet, with temperatures as low as 9 degrees early in the month, and the ground as sodden as in winter. Then in the last eight days of the month there was a complete contrast, with high pressure, sunshine and temperatures of 27 degrees.

May 2015 was also breezy, with lows until the 11th, then a two day high ridge, then a static low to the north east for much of the rest of the month that brought north westerly winds. But the weather was not particularly wet, with only two days that were really dominated by rain, and many days seeing some sun. Temperatures were in the mid to upper teens, rising at best to 20 degrees.

Lighter clothes at last

Generally, even if the weather is not cooperative, coolness in May is relative – in March similar temperatures would have seemed balmy and warm. Winds (with 2005 and the first half of 2010 and 2012 excepted) do not tend to be cutting. It can still be cold enough for an extra layer, but only one: this is the first month when one can go out for the day relatively lightly dressed.

When the weather is sunny, the outside tables of a pub or cafe are suddenly all occupied and the inside ones empty – the exact reverse of the situation for the previous six months. People start to stand around drinking outside city pubs, Towards the end of the month one starts feeling the need to use suntan cream for the first time and even to sit under the shade of trees.

Generally it longer gets sharply colder in the evening - temperatures typically are 9 to 10 degrees at night - but there are some exceptions and in 2005, 2006, 2007 and 2013 night time temperatures remained cool right up to the end of the month. By contrast 2008 had night temperatures as high as 15 degrees as early as the first week of the month.

Almost unnoticed, you are in the some of the longest days of the year. Lighting up time goes from 8.30pm to 9.05 pm during the month, but it barely seems to register, and one rarely seems to make the best of the extra daylight.

Bank holiday weather

May has two bank holidays  and it is almost axiomatic that at least one of them will have miserable weather. The question is, which one? In 2003, 2005, 2011 and 2014 the early May bank holiday was gloriously sunny, while in 2013 after an unsettled start to the Saturday the rest of the weekend was sunny, apart from a few areas of stubborn static cloud. In 2006 and 2008 there was sun and cloud.

In 2007, there was a miserable Saturday and a wet Monday, however, and in 2009 a sunny Saturday was followed by cooler, cloudier days with some drizzle on the Monday. 2012 saw a cold and grey early May bank holiday weekend, with rain on all three days and temperatures as low as 9 degrees. 2010 was also quite cool, with a mix of sunshine and rain. In 2007, a 38 day drought broke on bank holiday Monday with heavy rain. In 2015 Saturday and Sunday were cloudy and there was sun through high cloud on the Monday.

As for the late May bank holiday, it was largely dry in 2009, with a glorious hot Sunday with temperatures reaching 25 degrees, and and in 2013 the whole weekend saw blue skies, making this a very rare year when both bank holiday weekends in May were sunny. In 2005, temperatures on the Friday before the bank holiday reached a record 32 degrees – the first hot weather in a rather cool May - before cooling again over the next few days.

But from 2006 to 2008, the late May bank holiday was stubbornly cool and wet. 2007 saw temperatures as low as 8 degrees, or 5 degrees in the Chilterns, and in 2006 both the Saturday and Monday were grey and rainy. 2008 continued the tradition with a thoroughly wet and miserable Sunday and Monday, while in 2010 there was rain on the Saturday, cloud on Monday but a relatively sunny, if breezy, Sunday. In 2011 after a hot sunny Easter and early May bank holiday, the late May bank holiday was cool and cloudy with some rain, and in 2014 it was mixed, with showers on the Saturday, rain on the Monday but blue skies on the Sunday.

In 2015 all three days were cloudy, making this a rare year when both bank holiday Mondays were largely cloudy. Not quite so rare, however, as both were also cloudy and cool in 2016 and 2017. On the early May bank holiday Monday in 2017 there was also rain, which had started on the Sunday night and was quite welcome after a dry April. The weather also went downhill on the Sunday of the late bank holiday weekend that year, though both Saturdays were fine. The same was true of both Saturdays and the early May bank holiday Sunday in 2016.

In 2012 there was no late May bank holiday due to the Queen's Diamond Jubilee celebrations the following weekend, but had it been in its usual place, it would have been hot and sunny. The four day jubilee break at the start of June, by contrast, saw two days of heavy rain and was generally rather grey and cool.

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