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Sunday across much of the UK was one of the hottest on record. At Leeming in North Yorkshire, the maximum temperature of 27.2C (81F) was second only to the record which was set in May 1947, when the mercury soared to 28.9C (84F).

These high temperatures were all the more interesting when you consider it was only just under two weeks ago when I wrote that Leeming had recorded its coldest May night since 1967, and the second coldest on record, on the morning of Wed 13th May.

Other stations across Yorkshire have had similar extremes. At Pateley Bridge, which is not an official Met Office site but nevertheless an accurate station run by a local expert in the area, Sunday was the hottest since records began in that part of Nidderdale 27 years ago. Moreover, the contrast between the cold reported in Mid May, to this record heat, is a record in itself. The absolute temp range for this May at Pateley Bridge is 29.3C (-2.8C to 26.5C).

Hull in East Yorkshire also set a new record. Again, it's not an official station, but 29.4C (85F) was recorded on Sunday at a very reliable site run by a local expert. At the old Hull Met Office site, records which run from 1901 to 1971, the previous record was 27.8C. It's a remarkable temperature for a city on the Humber Estuary and so close to the influence of cold sea breezes at this time of the year.

But it's proved to be a very short lived hot spell. Indeed as I write, it's currently only 10C in the Vale of York as cool air from the Northeast makes a return.

For those still keen to know what the summer will be like, an interesting fact. As I wrote in my one of my previous blogs, there's been 23 cold winters since 1940; and only 2 have been followed by warm summers. That would suggest that although a hot summer is not impossible, it is certainly statistically very unlikely.

But one of the 2 years in which a cold winter was followed by a hot summer was in 1947. It's probably just a coincidence, but I found it interesting that Sunday was the hottest May day at Leeming since May 1947. Could history repeat itself, with 2010 following the same pattern as in 1947, with a warm summer to follow? Only time will tell.

Briefly onto global temperatures. I wrote in my last blog that global temperatures were high on all measures, close to the record values set in 1998.

The big question is how long will this heat last, and will it mean 2010 is the hottest on record, as predicted by the UK Met Office?

The graph below offers a few clues. It shows in blue the global ocean temperature anomaly, with the red line indicating the ocean temperature anomaly where the current El Nino has been occurring (an upwelling of warm water which adds to global temperatures). It shows a sharp drop off in the El Nino heat; with global temperatures starting to follow.

Several models are forecasting a La Nina developing later this year which would cause cooling. It's going to be a very interesting few months.

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Last night was the coldest May night for over 40 years. At the Met Office at Leeming, North Yorkshire, the mercury dipped to -3.5C (26F) making it the coldest since 3rd May 1967 when -3.8C (25F) was recorded - and the second coldest since records began shortly after the end of the 2nd world war in 1945.

It is interesting that the current record was set very early in the month - making the recorded temperature last night all the more remarkable.

Church Fenton in West Yorkshire also had their coldest May night since 1967.

Although April was above average from a CET (Central England temperature measurement) point of view, May is now well below average, and as we approach the half way stage of 2010 it is becoming clear that there is going to have to be quite a turnaround in UK temperatures for the whole of 2010 not to be colder than average.

This comes against a backdrop of warm global temperatures, on all measures. In fact so far this year, global temperatures as measured by satellites are only just below those that were recorded in the hottest year on record, in 1998.

Across the UK, next week looks much warmer than of late, with a continuation of the mostly dry, anticyclonic theme. If the models are correct, May on the whole looks set to be a very dry month.

This blocked weather pattern has mostly been in place since mid December of 2009. From a climatological point of view, It could be only a matter of time before a wetter, more cyclonic West to South-westerly type of weather becomes established for the first time since November of last year.

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Latest projections for tomorrow at 7am indicate that Ireland, Wales and the Southwest of England may well be affected by ash. Whether it affects flights of course depends on its density. Upper level winds suggest that the ash should start to clear southwards, with most of Ireland and the UK clearing accordingly through tomorrow and into Friday. With a general northerly persisting into the weekend and into the first half of next week, the volcanic ash should stay clear of the UK, although it may be a close run thing for parts of Ireland at times, especially into next week.

I have been asked numerous times just how long we could be affected by volcanic ash.

Dr Dave McGarvie who is a Volcanologist at the Open University told me earlier today about what history can tells us about Icelandic volcanic eruptions in the past.

"The current volcano (Eyjafjallajokull) erupted for just over a year from December 1821 till early 1823. It didn't erupt constantly all this time though, as after a week or so of intense activity it just sent out occasional minor explosions until end-June 1822 - when another sequence of substantial explosive eruptions started and lasted for a month till early August. It was quiet from then on (occasional explosions) and activity gradually died out early in 1823.

On June 26, 1823 the bigger volcano next to it (Katla, 25 km to the E) erupted. This was a small eruption by Katla standards and lasted for 28 days.

Historical record (last 1100 years) shows that three times Eyjafjallajokull erupted Katla has erupted soon after (c.920 AD, 1612, and 1821-1823). But it could be pure coincidence! After all Katla has erupted 20 times in that same time period. And each of the Eyjafjallajokull eruptions were different, so there's no common thread there. But the volcanoes are close to each other, and the lavas etc from both volcanoes overlap on the surface, so there could be a subterranean connection. Bottom line - we don't know enough.

The last substantial Katla eruption started 12 October 1918 and lasted 24 days. It produced an eruption plume an estimated 14 km (46,000 feet) high. A nice little injection of ash into the stratosphere of course, with a different set of problems to what we experienced in mid-April.

Katla is Iceland's second most active volcano, after Grimsvotn which lies within the Vatnajokull glacier. Katla has a habit of erupting twice a century, so that's why the Icelanders are a bit anxious about the length of time that's passed since 1918 - and whether this might mean a bigger eruption is due. However there's no correlation between the length of time that's passed and the size of the eruption because (for example) both of the eruptions in the 1600s and in the 1700s were amongst the largest recorded."

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This morning Irish airspace was affected by volcanic ash. This follows renewed activity from the Icelandic volcano. Latest information from the Icelandic Meteorological Office has confirmed an increase in activity from the Iceland volcano Eyjafjallajökull, erupting to a height of 18,000ft.

According to the Met Office there was a report from the Outer Hebrides yesterday evening of a milky sky, and in the early hours Tuesday of volcanic dust was detected at 9000ft in the same location.

The latest projection shown below for 7am tomorrow morning shows most of Scotland and parts of Western England affected by volcanic ash, roughly from Newcastle through Manchester and south to Exeter - though of course it remains to be seen whether it's thick enough to affect air traffic.

The wind direction at 20,000ft is mostly from the north, shown below. This would mean that the area of ash across Scotland, and the area to the north of Scotland, may be dragged across other parts of the UK later tomorrow and into Wednesday.

Of course even if volcanic ash affects more areas tomorrow, it's again worth pointing out that it's the density of volcanic ash that is of critical importance. So more flight disruption is not a certainty, although it is certainly possible, in the next few days.

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