Convective infill

The convective infill that has affected inland parts of southwest England, has spoilt what started off as rather a lovely day. Having said that it appears that a similar thing has happened but on a much larger scale over Ireland this afternoon, as the whole country seems to be under a sheet of CUSC.

North Atlantic hurricanes – reviewing last season and looking forward to 2017

Figure 1 – Hurricane Sandy courtesy of NASA

The 2016 North Atlantic season ended up being slightly above average, with seven of the fifteen tropical storms reaching hurricane status, there were three category 1’s, two category 3’s and a category 4 & 5 hurricanes (fig 3 & 4). It was the highest number of hurricanes in a year since the ten in 2012.

Figure 2 – Raw HURDAT2 data courtesy of the NHC

Some of the tropical cyclones in 2016 were very long-lived. Hurricane Nicole survived over 15 days, and Hurricane Alex, which started life on the 7th of January, and became the first Hurricane to form in January since 1938, travelled almost nine thousand nautical miles in its ten-day life.

Figure 3

The most severe Hurricane of the season was undoubtedly Hurricane Matthew, which flirted with the eastern seaboard of the United state and reached category five status in so doing , the first category five hurricane since 2007.

Figure 4

I always reckon the best way to compare individual years is by the combined ACE of all tropical cyclones (fig 5), and using that as a yardstick 2016 was the most active year since 2010.

Figure 5

2016 Predictions

If you want to look at the NHC Forecast verification report for 2016 be my guest, you can find the PDF of the report here. To me, it tells you very little about the season, or what the verification says about the various forecasts that the NHC made. I love the old fashion verification system which has just two outcomes, right or wrong, hit or miss I’m afraid. Most of the pundits who made a prediction for how 2016 would turn out were generally correct, including me!

  • Accuweather weather 14/8
  • Met Office 14/8
  • NWS ~ 13/6

Those aren’t the odds but the count of North Atlantic tropical cyclone/hurricanes in the 2016 season, which ended up 15/7.

2017 Predictions

I’ve managed to find some early predictions for 2017 courtesy of Wikipedia

  • Tropical Storm Risk 11/4
  • Colorado State University 11/4
  • The Weather Company 12/6
  • North Carolina State University ~13/5

The general consensus from them is that it’s going to be an average season, although the big players haven’t thrown their hats into the ring yet, probably because the season doesn’t officially start till the 1st of June. The season has already started though because we’ve already seen one tropical storm this month already.

Late April cold spells and the Easter Snowstorm of 1908

Figure 1 – Lymington High Street – April 25th 1908 (courtesy of lymington.org)

Easter in 1908 fell late, so the snow that fell over much of southern England must have come as a big surprise on the Easter Sunday on the 19th of April (fig 1). The following week was intensely cold for late April, and there were periods of heavy snow across much of southern England. In an article in the Met Mag of May 1908, Fred J Brodie said this about the snow at Oxford:

The conditions at Oxford are interesting in a special degree on account of the length of the meteorological records at the Radcliffe Observatory which run from 1853. The depth of snow there was 17 inches, and the only instance of a greater amount being recorded at any time of year was on February 13th and 14th, 1888, when 24 inches of undrifted snow was measured.

I love the comment that Fred went onto make a few lines further on…

The practice of comparing, for the purpose of record making, observations made in two different localities is not to
be commended…

He of course is completely right in what he says, but he must be spinning in his grave these days, on the goings on in the early 21st century with extreme temperature records I would have thought, because no one, and that includes myself seems to give a hoot these days about comparing extremes from weather stations without knowing thinking much about their actual location. You can find an article about the events of April 1908 on the Weather Outlook forum, which includes details of snow depths recorded at the time, plus a lot of other information and photographs about the blizzard. The Weather Magazine of December 1981 also had an article about April 1908 in which it linked it to the April of 1981 and said:

The marked similarity of the graphs for 1908 and 1981, especially in the second half of each, is confirmed by a correlation coefficient of 0.93 for the last 15 days of the month. For the full month the correlation coefficient is 0.65. The weather of late April was remarkably similar in these years.

Since 1981, the daily CET series may well have undergone some slight modifications, but there is most definitely a cold spell that occurred during at the second half of each month, the minimum CET in 1908 was a couple of degrees colder than it was in 1981 though, and those on the 24th and 25th still hold the record for lowest minimums on those two days (blue stars). Personally I only see a broad similarity between the two, I’ll have to spend some time and write some code to generate a correlation coefficients between these two months and see what I come up with. If you look closely at the graph of CET (fig 2), you’ll notice that in just over a week, maximum anomalies rose from around -8°C to +8°C. The resultant rapid thawing of lying snow from the week-long cold spell lead to great flooding in places along rivers in the southeast especially the Thames, and the Great Ouse at Buckingham.

Figure 2

Synoptically, the 25th of April in both 1908 and 1981 were slightly similar in that they were both cyclonic in nature.

Figure 3 – Courtesy of NCEP/NOAA reanalysis

But up aloft in the atmosphere the cold air of 1908 was much deeper than it was in 1981 (figs 4 & 5).

It seems cold outbreaks towards the end of April are not at all uncommon, I’ve just picked on probably two of the more extreme events. Next week promises its own cold outbreak (fig 6), but synoptically, if the GFS model is correct, it will be more of a cold northerly rather than cyclonic as it was either in 1908 or 1981.

Figure 6 – Courtesy of OGIMET

 

Q: Just why has April been so dry & sunny?

Q: Just why has it been so dry and sunny and dry this April?

Figure 1 – Data courtesy of NCEP/NOAA reanalysis

A: Because for the first 18 days of the month there has been a large (+11 hPa) positive MSLP anomaly sat just to the west of Ireland (fig 1). As I reported earlier this month (never thinking that the first half of April would turn out as anticyclonic as it has), 1938 was the most anticyclonic in records that started in 1871 (fig 2). The two April’s are indeed very similar, but the anomaly chart for 1938 was for the entire month, and not just the first 18 days, and were larger and even more pronounced. That’s not to say that the second half of April 2017 won’t continue to be just as anticyclonic as was the first.

Figure 2 – Data courtesy of NCEP/NOAA reanalysis

I’ve just put quite a lot of programming effort into the program that I use to download, parse and visualise reanalysis MSLP data from NOAA, so hopefully I’ve got things right. The LTA that I have used to calculate the anomalies for years 2012 or earlier is for the whole of the 20th Century i.e 1901-2000. For the years after 2012 the LTA is for the 66 year period 1948-2013. This is because the older reanalysis data uses a 2 x 2° grid, whilst the data after 2012 is from the 20th Century reanalysis on a 2.5 x 2.5° grid.

Jersey the sunny Channel Island

Figure 1 – Courtesy of vintagerailposters.co.uk

Jersey have taken over at the top of the sunshine league this April, with almost 9 hours of sunshine each day for the first 20 days of the month. Their total of 178.6 hours so far is I estimate 66.1% of the possible maximum total. It’s not been sunny everywhere across the British Isles, but without detailed climate statistics to produce anomaly values it’s impossible to be precise, but as usual, it seems to have been duller the further west and north that you are so far this month (fig 2).

Figure 2

Recent cloud images

Here are some of my recent cloud images, it’s been a bit quiet as far as my photography goes this year, we seem to have missed out on any good sunsets. Last night was an exception though, not a colourful sunset but rather a broody dark display of SC with embedded mammatus, the base of the SC sheet was at around 5,000 feet according to the LCBR at Exeter airport.

It all ties in with the cloud in the visible satellite image of the same time that’s aligned ENE-WSW across southern England (fig 1). The 18 UTC analysis has a corresponding trough following behind the warm front on the analysis (fig 2), the bottom bit of the warm front is marked frontolysis by the Met Office no doubt because there is no cloud on it west of 1° east. There were some showery outbreaks of rain along the trough yesterday evening, so there must have been some instability associated with it as it moved SSE ‘ward (fig 3).

Figure 1 – Courtesy of the Met Office & EUMETSAT

Figure 2 – Courtesy of the Met Office

Figure 3 – Courtesy of the Met Office

A little white lie from the Met Office

Quite a lot of things annoy me about the Met Office as regulars readers of this blog will have no doubt picked up over the years. One of the worst traits that they have, is when talking about climate statistics for the UK, they use the following phrase:

“When records began in 1910…”

When you know full well that detailed records existed much earlier than that. What they ought to say, which is much close to the truth, is:

“We’ve only managed to digitize records back as far back as 1910, and even though we hold detailed climate records that go as far back as the early 1850’s, we can’t be bothered to do anything with because we’ve already spent the money on a big new shiny supercomputer.”

There is a classic example of that on their website today concerning the occurrence of frost in the UK during April.

Figure 1 – Courtesy of the Met Office

“Detailed frost recording in the UK began in 1961”. What a shocking admission for the national weather service of a country that was established in 1854. That must mean all of the sterling work done by meteorologists before 1961 was all in vain and a complete waste of time. What happened to all the temperature records between 1854 and 1960? At random, I picked out a copy of the DWR for January 1917 just to see if there were any extreme temperatures reported back then, and unsurprisingly there they were, for thirty-three stations across the British Isles (fig 2). Of course that’s just the tip of the iceberg, because like today, many more climatological returns from stations remain unpublished and go straight into the archives.

Figure 2 – Courtesy of the Met Office ©Crown Copyright

Absolutely no excuse

The Met Office were one of the first big users of computers and still are, here is a list of the computers that they’ve used down through the years (fig 3). I realise that looking forward with NWP model is vital, but so is looking back, and treasuring the climate data that previous generations have made since 1854. But why is it that climate records have always seemed to have been neglected, and climate data limited and inaccessible when there seems to have been no lack of one of the world’s fastest supercomputers at their disposal?

Figure 3 – Courtesy of Wikipedia

The Met Office have the resources, both in terms of staff and computing power to digitize the rainfall, temperature and sunshine records of the past and extend the gridded data series that they already have, back at least 50 years before 1910, but they have chosen to leave that wealth of old climate data untapped, and for the life of me, I just can’t understand why?

Ne’er cast a clout till May be out

Figure 1

Another touch of frost in places overnight, with air temperatures down to -1.8°C across the southeast of England this morning (fig 2). There has been a more general and sharp ground frost across most of the southern and eastern England too (fig 1), which won’t have please a lot of gardeners.

Figure 2

In fact the cold air at the moment is quite widespread across much of northern Europe and eastern Russia (fig 3), nothing exceptional, but because it comes after another relatively mild Winter and Spring so far, it’s come as a bit of a shock to some. And remember – ne’er cast a clout till May be out.

Figure 3

The driest Aprils since 1910 by region

I’ve spent a bit of time today creating an infographic of driest April’s. I’ve used the free data set maintained by the Met Office, which started in 1910 and is produced from gridded data for ten regions across the country. Hopefully one day the Met Office will extend this series to cover all the rainfall data that they inherited from the British Rainfall Organization in 1919 and just sat on for the last 98 years. I knew about the very anticyclonic and dry April of 1938 from a previous article that I had written earlier this month, but hadn’t realised that it was only driest in three out of the ten regions, even though it was the driest April in the EWP monthly series that started in 1766. The 1.0 mm in East Anglia in 2007 tops the list of driest region by region, which is something else I missed. I’ve borrowed the regional map from the Met Office, I’m sure that they won’t mind, let me know if you spot any issues.

Data courtesy of the Met Office

Later….

What’s slightly puzzling about these figures for April is why the UK value is the highest April value for all regions at 14.1 mm, when it’s made up of the value for Wales 8.8 mm, and the value for England 6.7 mm. Both values are for the same year 1938, I would have thought that the combined UK value should be some kind of mean of the two, but obviously not. It must have something to do with the gridding I suppose.

18 April – Sharp frost in north

 

Not a perfect radiation night across Scotland, there was always a little too much residual gradient left over from yesterday, even with a high pressure cell sat right slap bang over the country. Despite this Tulloch Bridge still recorded an overnight minimum of -5.7°C [06-06] which is not bad going for mid April (fig 2).