Latest April 2017 rainfall totals

You’re all probably all getting fed up to the back teeth hearing me prattle on about what a dry first half of April it’s been, so I’ll let the graphic do the talking.

Accumulations from available SYNOP – Data courtesy of OGIMET

April snow for Cairngorms

Figure 1 – Cairngorm from Loch Morlich courtesy of © Winterhighland Limited

It’s proving to be a cold and showery Easter over Northern Scotland this year, and the showers affecting the area on Saturday afternoon look like they are putting snow down to ~3000 feet if this webcam image is anything to go by (fig 1). That’s because the cold air over Scotland is holding the air temperature on Cairngorm at a very cold -2.9°C (13 UTC) at the moment. The heatmap of air temperatures on the summit since the start of March shows that until this last week, it had been relatively mild since around the 24th of March (fig 2). It looks like the high ground might get a bit more snow overnight, but it might be a bit late to extend the skiing season from what I can see from the other webcams in the area.

Figure 2

At the same time it’s been quite a benign Spring as far as gales and storm force winds are concerned on the summit (fig 3).

Figure 3

Absolute drought frequency in the British Isles

Figure 1 – Courtesy of the Met Office ©Crown Copyright

I was interested in the average number of droughts they were each year across the British Isles and came across an article in an old Met Mag (vol 76 No 903. September 1947) with the above maps of droughts for the period 1906 to 1940. These might be old climate stats but that doesn’t mean they have no value. Back in 1887 the British Rainfall Organisation introduced the following definitions for absolute and partial drought:

  • An absolute drought is a period of at least 15 consecutive days, to none of which is credited 0.01 inches of rain or more.
  • A partial drought is a period of at least 29 consecutive days, when the mean daily rainfall does not exceed 0.01 inches.

I assume that the partial drought limits the total of rain in any 29 day period to less than 0.29 inches (~7 mm) but I’m guessing, the definitions will have no doubt been changed since 1947, but I have no idea to what. The chances of an absolute drought of 15 days or more (which some stations this April have at the moment) looks to be highest, as you would expect, across the southeast of England, and south of 52° north the average looks to be around 1 or 1.2 occurrences a year. Curiously, there doesn’t look that much overall difference between the map of absolute drought and the map of partial drought (fig 1).

It’s refreshing to see that climate maps in 1947 included the whole of Ireland as well as the rest of the UK, it’s a shame the head of international climate service development at the Met Office can’t get around to talking to his counterpart at Met Éireann and share our climate data! Perhaps if we make this a stretch target or SMART goals for Dr Chris Hewitt (who I believe is the present incumbent in this role) he will make it happen. Weather and climate know no man-made political boundaries, or it didn’t the last time I looked.

Saturday 15 April 2017 – Dry spell hangs on despite overnight rain

 

Figure 1 – Data courtesy of the Met Office

The dry spell and absolute, or ‘meteorological’ drought as it’s known these days is just hanging on despite some overnight rain across the country (fig 1). St James Park in London last had >0.1 mm of rain 17 days ago, but as always the rainfall data in the SYNOP data can be omitted or the observation missing at times. Linton-on-Ouse in the Vale of York got away without any overnight rain, as did a few other stations including Exeter as far as I can tell (fig 2). Please post a comment if you know any different.

Figure 2

Figure 3

As far as I know, St James Park only reports 24 hour rainfall totals at 06 UTC each day, and it’s rarely missed so far this year. The accumulation for 2017 is currently standing at 135.2 mm (5.32″) for the last three and a half months. Looking more closely the last real rain was 7.2 mm on the 23rd of March, so I make it, barring an instrument malfunction, they’ve had 0.2 mm of rain in the last 22 days (fig 4). I’ve got a strong feeling that they won’t get away with it tomorrow, although Exeter might just get away with a trace.

Figure 4

 

A night to remember – 14/15 April 1912

Figure 1 – Courtesy of Wikipedia

The RMS Titanic sank in the early hours of Monday the 15th of April 1912, after striking an iceberg at 11.40 am on the previous evening. The exact date and time it struck the iceberg fixes the time of the disaster, which depends on which time zone that you use. If you get a chance, I read a short but fascinating article about the disaster on the Encyclopedia Britannica web site. There is so much written about the event that there are literally hundreds of articles available on the Internet. Wikipedia, as you would expect has a complete and detailed report about it, 10 things you might not know about RMS Titanic  and the Titanic Facts websites also make interesting reading.

Titanic was south of Newfoundland that evening, and steaming at almost full speed (22.5 knots) west south-west after ’rounding the corner’ and heading on a Rhumb line for New York (fig 2). Who knows, if the First Officer William Murdoch hadn’t try to avoid the infamous iceberg and Titanic had hit it head on, rather than as we know with a glancing blow, that created a series of holes below the waterline in five of the ship’s watertight compartments, this disaster may never have occurred.

Figure 2 – Courtesy of Mark Chirnside

All I can offer about the weather at the time of the sinking, apart from that we know it was a clear and starry night, and the sea was like a mill-pond, is the midnight chart for the 15th of April, which I’ve generated using the 20th century reanalysis data (fig 3).  Titanic as you can see was in a col like area between two anticyclones in a belt of high pressure that stretched right across the North Atlantic that night, winds will have been light and from the northwest, rather spookily weather reports from ships in the North Atlantic at that time may well have been used in this reanalysis.

Figure 3 – Data courtesy of NOAA/NCEP 20th Century Reanalysis

In an eye-witness account from Jack Thayer a 17-year-old survivor, who said:

It was a brilliant, starry night, there was no moon and I have never seen the stars shine brighter; they appeared to stand right out of the sky, sparkling like cut diamonds. I have spent much time on the ocean, yet I have never seen the sea smoother than it was that night; it was like a mill-pond, and just as innocent looking, as the great ship quietly rippled through it.

Figure 4

The risk of icebergs was well-known in April in that part of the western North Atlantic (fig 5), and if the Captain of the Titanic had only done what the Captain of the SS Californian had done, and that was to stop the ship overnight, or at least slow it things might have been so different.

Figure 5

  • Interestingly the SS Californian was later sunk herself, in November 1915, by a German submarine, in the Eastern Mediterranean during World War I.
  • Titanic’s sister ships HMHS Britannic struck a mine in the Aegean Sea also in the first World War, and sank in a similar way to how her sister ship sank four years earlier.
  • Titanic’s other sister ship lead an interesting life, RMS Olympic was used as a troop ship in World War I, and collided and managed to sink a German submarine. On the 15th of May 1934 she managed to collide with something else, this time the Nantucket lightship (see map fig 2) with the loss of seven lives, her final voyage ended when her hull was towed in for scrap at Inverkeithing in September 1937.
  • In July 1918, the RMS Carpathia which played such a big part in rescuing so many of the survivors from the Titanic, was herself torpedoed by another German submarine U-55 in the Celtic Sea.

It certainly was a dangerous life for any merchant seaman back then.

El Niño latest

Figure 1 – Courtesy of NCOF

The coastal waters off the coast of Chile seem to have cooled down since last month. There were SST anomalies 0f +5°C on the chart for the 18th of March last month (fig 1), but the highest that I can see in the same area is +3°C twenty five days later (fig 2). The experts are saying that an El Niño event still remains a distinct possibility towards the end of this year though.

Figure 2 – Courtesy of NCOF

I’m no expert and don’t pretend to understand why the cold Humboldt current seems to be the controlling mechanism for the upwelling of warmer water off the coast of Chile (fig 3).

Figure 3 – Courtesy of Wikipedia

But this map I found after a little research on the Internet indicate that there are more than just the Humboldt current at play down the coast of South America (fig 4).

Figure 4 – Courtesy of CALEB

I shall of course try to find out and report back, unless one of my readers would like to do it for me.

Dust Storms

Image 1 – Courtesy of the BBC

I watched a fascinating documentary on BBC4 the other night about dust storms and what a serious risk they pose to people’s health, especially in the Middle East, dust storms might look dramatic but they must make people’s lives a misery. I liked the matter of fact tone of the documentary, which is in marked contrast to many other ‘scientific’ documentaries that you see from the BBC about weather and climate in recent years, that’s probably because it was a program made for the BBC World service.

Apparently the Sahara is the source of 50% of all dust in the world’s atmosphere, and 25% of dust storms can be attributed to man, but it’s something we can do something about, if countries can only work together. I had heard about the ecological disaster that man had made of the Aral Sea in the early 1960s, but Lake Urmia in Iran was news to me, a terminal salt lake that’s shrunk to less than 40% of its former size is yet another disaster to add to that list, and because the fine particles from the sediments in the dried out lake bed are an ideal source of dust in storms because they can be so easily lifted by the wind.

You can find the program on iPlayer for the next month and I encourage you to watch it. 

Image 2 – Lake Urmia courtesy of the BBC

The drought in the southeast

Figure 1 – Consecutive dry days (13 April 2017)

The overnight rain in some places put an end to any possible drought across the country, but as far as I can see both Wattisham in Suffolk, and St James Park in London have now gone 15 consecutive days with less than 0.2 mm of rain in any day, so are technically in drought, and when I say drought, that’s the old-fashioned meteorological type. It might not last very long though, because the GFS is forecasting rain from a cold front moving south during Friday, which might scupper the drought before it even gets going. Looking beyond Friday though, the same model predicts anticyclonic conditions returning and persisting till at least the 21st, so we could be in for a very dry April in some parts.

Extreme Easters since 1772 in Central England

Figure 1 – Data courtesy of NCEP/NOAA 20th Century Reanalysis

The Met Office beat me to a story about extreme Easters of the past, but undaunted, and without the masses of climate data they have at their disposal, I pressed on with a bit of research of my own.

Because Easter is not at a fixed time each year it’s difficult to compare one with another. Easter Sunday can fall as early as the 22nd of March or as late as the 25th of April. I’ve used the daily CET series from 1772 (now there’s a surprise), and calculated a five-day mean, from Maundy Thursday to Bank Holiday Monday to do my comparison with. Because of the time range that easter can fall, I have base it on mean temperature anomalies rather than the mean temperature. So from what I’ve found the coldest Easter period since 1772 occurred in 1892 (fig 3). The Easter Sunday that year fell on the 17th of April so it was by no means early.

Figure 2 – Data courtesy of the Met Office

The mean temperature for the five days between Maundy Thursday and the Bank Holiday Monday in 1892 was 2.1°C, which was -6.4°C below the long-term average for that period (fig 3). The weather chart for the Sunday (fig 1) shows just what a bleak and cold Easter that must have been in eastern parts.

Figure 3 – Data courtesy of the Met Office

I couldn’t resist including the Monthly Weather Report for April 1892 after using it to check out my story because I was taken with some of the phrases that were used by whoever wrote the report. I have highlighted some of them from the PDF that I accessed courtesy of the Met Office (fig 4). The remark about Vapour Tension exceeding 0.25 on the south coast of Ireland and England was a real charmer, I bet sixpence was a lot of money in 1892, and what happened to the Weekly Weather Report?

Figure 4 – Courtesy of the Met Office and ©Crown Copyright

Conversely, the warmest Easter using the same method, fell in 1926 in Central England at any rate.  Easter Sunday that year fell on April 4th, and the five-day mean was +6.5°C above today’s long-term average, and if you look at the synoptic situation (fig 5) you can understand why. I did look for any weather related news for Easter 1926, and mistakenly thought that this was the year of the Easter Rebellion in Ireland, but I was 10 years too late, that occurred in 1916.

Figure 5 – Good Friday 1926, data courtesy of NCEP/NOAA 20th Century Reanalysis

Dry start to April continues…

Here are the number of consecutive dry days (<0.2 mm) across the southern half of the British Isles I’ve compiled from SYNOP reports. This is my best shot, some sites have missing observations, some have missing rainfall reports, and I have noticed that the AWS the Met Office employ are very sensitive and have a preponderance to push out a 0.2 mm report, when a trace or 0.1 mm might have been more appropriate. I reckon that’s the case at many stations, take Exeter Airport for example, some very good radiation nights in the last week could easily knock up 0.2 mm of dew in the gauge, and as this count is for days with less than 0.2 mm each day, so the total gets zeroed, and we have a count of 3 days instead of 8 or more.