15 May briefing

Western Ireland saw the heaviest rain overnight, more specifically the higher ground of counties Kerry, Mayo and Donegal seeing accumulations of more than 75 mm (fig 1).

Figure 1 – Estimated rainfall totals from Weather Radar Images

Rain is holding the temperatures down in the southeast, but I notice that there’s much warmer air just across the Channel (fig 2) at 09 UTC.

Figure 2

There was a little bit of rain overnight in the southeast but not nearly enough, but the cold front will drag its heels this week though, and could take till Thursday to clear the southeast, and if the GFS model is correct, will produce a wet day on Wednesday across the south (fig 3).

Figure 3 – Courtesy of OGIMET

What’s the sunniest month of the year?

I thought that I would investigate and find out exactly what climatologically is the sunniest month of the year using monthly sunshine data from the Met Office. The gridded sunshine record only started in 1929, but I’ve been reliably informed by someone in the know at the Met Office, that plans are well advanced to extend this (along with the rainfall and temperature series), back to at least the start of the 20th century, which I applaud, although in my opinion it’s a long way overdue. The add-on to my application looks not only at sunshine, but rainfall and temperature too, and for any region within the United Kingdom. The pie chart I’ve include is for England & Wales (fig 1), and reveals, surprisingly to many I bet, that May is climatologically the sunniest month of the year in 35.2% of years since 1929, followed by June in 31.8% of years, and July in 19.3% of years.

Figure 1 – Data courtesy of the Met office

Also rather surprisingly, it can happen that in some years April is the sunniest month. According to my application that’s occurred five times, in 1945, 1954, 2002, 2007 and 2011, so three times in the last 15 years. There’s always a chance that I’ve made an error let me know if I have.

The sunniest month in the entire England and Wales record was the July of 2006 with 287.6 hours of sunshine (fig 2). The sunniest month in the famous summer of 1976 was also a July with 251.5 hours of sunshine, but ranked only 13th in the list of sunniest months in a year.

Figure 2 – Data courtesy of the Met Office

The sunniest May’s in the UK since 1929

What was the sunniest May in the UK? That of course depends on where you live, so using the regional gridded sunshine data series from the Met Office that started in 1929 here is a map of the sunniest May for each of the nine individual regions, and for the whole series in a horizontal bar chart (fig 1). May is climatologically the sunniest month of the year in the UK, but more of that in an upcoming post, and by the look of it, the May of 1989 was the sunniest in nine of the seventeen regions, including the UK and England and Wales, if the gridded sunshine values are anything to by.

Figure 1 – Data and map courtesy of the Met Office.

The 1989 record certainly is in no danger of being broken in the southeast this year, but it’s certainly could in Northern Ireland and the west of Scotland, where they’ve got off to a flying start (fig 2).

Figure 2

The correlation between precipitation and air pressure

Figure 1

The pressure has fallen surreptitiously and steadily over the last few days here in the southwest, from around 1028 to 992 hPa without most of the population probably even noticing, unless of course they still have a hall barometer that they tap before going out to work, but that’s my very old-fashioned 1950’s suburban view of the world, that’s all but gone in these days of smartphones and tablets.

That fall of pressure and the recent dry spell, got me thinking about the obvious close correlation that exists between air pressure and precipitation, so I thought that I would overly the pressure and precipitation in a single graph, and hey presto a new graph, which I call a baro-hyetograph for want of a better word, is born. The top baro-hyetograph is for the period since the start of the year for Exeter airport, and shows the recent dry spells and anticyclonic periods very well (fig 1). The second baro-hyetograph is for Heathrow airport and paints a very similar picture (fig 2).

Figure 2

Interesting trajectory

The interesting curved trajectory that the showery rain took overnight left most of Devon reasonably dry (fig 1), although we might not be so lucky today. The rain must have come as a shock to some northwestern areas, and today’s cloud puts an end to an eleven day spell of sunny days.

Figure 1

Many places still without rain this month

Many places across the British Isles, especially over Northern Ireland and Scotland are still without rain this month, as the dry spell that started in late March continues.

Figure 1

All change

Looking at guidance from the latest NWP generated from the GFS model shows that the weather is now on the change, with a more cyclonic southwesterly spell for this weekend and the early part of next week, before high pressure rebuilds in the mid Atlantic by the end of next week.  In fact the forecast for next Monday (fig 2) looks quite windy and wet, especially across the west, although the southeast does look like it will escape the worst of the rain.

Figure 2 – Courtesy of OGIMET

Having said that, the Met Office in their forecast charts for Sunday night don’t develop this feature quite so deeply (fig 3).

Figure 3 – Courtesy of the Met Office

Wonderful start to May in Northern Ireland

It’s been a wonderfully sunny start to May in Northern Ireland, with Aldergrove recording 133.3 hours of sunshine in the first 10 days of the month. They have now jumped ahead of the ‘Sunshine Island’ of Tiree as the sunniest place in western Europe this month, with Alicante now close behind in fifth position (fig 1). In stark contrast, the dearth of sunshine in the southeast is quite noticeable in the chart, with just a measly 33.7 hours of sunshine so far this month at Wattisham.