What a difference six weeks can make

Figure 1

There’s a very similar circulation pattern in control of this weeks weather to the one at the end of February, with an anticyclonic easterly flow affecting all parts (fig 1). The big difference is that the air mass at the end of February was much colder, but additionally spring has sprung, and Eurasia has warmed, so the 06 UTC anomalies look very different (fig 2) despite the warming or cooling effect of the North Sea.

Figure 2

My meteorological heroes

Figure 1 – Courtesy of the WMO

I have a few ‘meteorological’ heroes in my life, and it may come as a surprise to many that Peter Ewins or Julian Hunt don’t feature in the list. At the top of it must come Gordon Manley (1902-1980), whose name I first came across when reading his 1952 book ‘Climate and the British scene’ as a teenager. He is best known for his work on reconstructing the past climate of Central England with his CET series, which was adopted and sanitized by the Met Office, which I noticed that he joined in 1925, but had the good sense to resign the very next year!

Along side Manley at the top of my list of meteorological heroes is Hubert Lamb (1913-1987). It was Lamb who catalogued the circulation patterns across the British Isles from 1861 and came up with the idea of ‘Lamb’ weather types, which as far as I know extended the earlier work on weather types done by Van Bebber and Gold. That work has been carried forward by the CRU at the UEA, although they switched to an objective rather than Lamb’s original subjective way of classifying each days weather type. In 1964 he was asked to write a new edition of a book called the ‘English Climate’, another very readable book that I first came across when I joined the Met Office. Lamb did work on and off for many years with the Met Office, in fact from before the war until 1971. The second world war was a problem for him because as a Quaker he couldn’t directly get involved in it. The answer was that he work in the Republic of Ireland for the duration of the war with Met Éireann. He finally saw the light late in his career, and had the good sense to leave the Met Office for academia and launch the CRU at the UEA.

Looking at both of my heroes, I can see the connection between the two is that they were both instrumental in creating important climate data series with the CET and LWT. For some reason that appealed to me, and as soon as I had invested in a BBC micro in 1982, it was the first thing that I felt impelled to write a program for – the rest as they say is history!

The connection between these two esteemed gents and myself, apart from our innate love of the climate and weather of the British Isles and resigning from the Met Office, is a fondness for its hills and mountains.

So when I came across an interview with Hubert Lamb recently on the WMO website I just had to include some of the more interesting questions that he was asked. It was in a publication called the Bulletin Interviews and here are a few of the questions that he was asked that I found interesting. As far as I can see the interview took place before 1981.

Figure 2 – Courtesy of the WMO

Hands up how many of us have a love of weather that started when we experienced a snowy winter as a child?

Figure 3 – Courtesy of the WMO

I never realised that Richardson was also a Quaker, he too would also feature in my list of meteorological heroes.

Figure 4 – Courtesy of the WMO

This story of Lamb’s reminds me of the thick smoke haze that we would get in the Vale of York when I started my observing career at RAF Leeming in 1970. I can still remember reporting 800 metres in smoke behind a light northeasterly sea breeze that was blowing down from Middlesbrough. Thankfully things are a little cleaner these days.

Figure 5 – Courtesy of the WMO

It’s a shame that the Met Office don’t share Lamb’s passion for past climate data, they’ve recently left the digitising of the DWR records to the Weather Rescue volunteers. What would Lamb have thought? No wonder he left.

Figure 6 – Courtesy of the WMO

I like the bit where he says about climate warning – “…there is also the dangerous tendency to think that Man is responsible for all occurrences. That should be viewed with considerable scepticism“.

Unfortunately the ‘Bulletin interviews’ doesn’t feature an interview with Gordon Manley which is a shame.

Weak weekly cycle in Central England

Regular readers of this blog will know that I’ve been boring them with an approximate weekly cycle of northerly outbreaks occurring each Sunday for the last four weeks (fig 1).

Figure 1 – Courtesy of the Met Office

I thought that I would take a look at the provisional daily CET anomalies to see if I could pick out the cycle in it, which if you squint your eyes a bit, you can just about make out in the mean anomalies (fig 2).

Figure 2 – Last 3 months daily CET anomalies

Looking at the latest forecast for Sunday, it looks like the cycle may be struggling to manage to produce a NW, so that might be the end of another bright idea of mine!

A true northerly

Figure 1

You don’t often see a true northerly so I thought that I would try to capture the moment for posterity. I’m sure that “it’s streaming Arctic air straight from the North Pole” but the less said about that cliché the better. It’s interesting to see from the plotted chart that even though the gradient maybe 020°, the surface wind is still backed NW across most inland stations (fig 1). A regular feature in this kind of flow is the plume of showers that stream down the Irish Sea, and it’s there today clearly visible in the satellite image (fig 2).

Figure 2

At 11 UTC the stream starts midway between the Isle of Man and the Northern Ireland coast and stretches southward down to western Cornwall. There also seem to be two distinct parallel lines of showers to the west of Wales that you can see in the weather radar (fig 3).

Figure 3

Atlantic SST – Is this the end of the cold blob?

Figure 1 – 24 November 2015
Figure 2 – 27 November 2016
Figure 3 – 22 November 2017

You can tell just by looking at these sea surface temperature charts since 2015 (figs 1-3) that there’s been considerable warming going on in the last two years. The cold anomaly that was a feature for so long in the central Atlantic is now less intense and much smaller a feature than it once was. It’s shifted and has been squeezed further northeast towards the southeast coast of Greenland and the opening of the Labrador Sea.  The other notable difference that’s appeared in recent months is the area of warmer SST anomalies ~1500 km to the west of Portugal (42N 17W), a warm blob if you like.

The warm blob and this coming winter

To be honest I don’t have a clue if this warm blob will have the slightest effect on the weather in the British Isles this coming Winter. It would be nice to think that the area of warmer SST might weaken the Azores high in some way, and that might increase cyclonic development in the southeast Atlantic which will run northeastward towards Biscay – who knows. Looking at the actual MSLP anomalies (fig 3) for so far this month, it’s true that the Azores high is displaced further to the northeast, but all this has done has been to increase the strength of the zonal flow across the Atlantic. In fact everything seems to be enhanced in some way, if you look at the underlying anomalies (red dashed line) both highs and lows have been more intense in the first three weeks of November 2017 than usual.

Figure 3 – Data courtesy of NOAA/NCEP reanalysis

A cycle of northerly Sundays

Figure 1

If you examine the forecast chart for tomorrow and next Sunday, you might be forgiven for thinking there is something of a weekly cycle going on here (fig 1), both days are northerly, in fact next Sunday is a cyclonic northerly worthy of any cold spell in winter worth it’s salt. And if you look back over the last two weeks (fig 2), you’ll notice that both the 29th of October and the 5th of November had northerly tendencies too.

Figure 2 – Courtesy of the Met Office

Of course it’s all just chance, but just out of scientific curiosity, I’ll be keeping a close eye on the weather pattern for next Sunday, just to see if we can manage four successive northerly Sunday’s.

  • 29th October [N]
  • 5th November [N/NW]
  • 12th November [N] (forecast T+24 but odds on)
  • 19th November [CN] (forecast T+192)

The most anticyclonic November

Figure 1 – Data courtesy of the CRU/UEA

November is not renown for being an anticyclonic month in the British Isles. As you can see (fig 1), November is one of the few times in a year when cyclonicity is on a par with anticyclonicity. So looking at a ranked list of anticyclonic November’s since 1871 (fig 1), the number of any November’s that are over 50% anticyclonic (when using the Objective Lamb Weather Type as a crude measure) is quite small.

Figure 2 – Data courtesy of the CRU/UEA

As you can see, joint top of the list of most anticyclonic November’s along with 1942, is the year 1988, when 15 of the 30 days were pure anticyclonic.

Figure 3 – Data courtesy of the CRU/UEA

An anticyclonic Autumn month in November can only spell mean one thing as regards weather is concerned – frost and fog – and 1988 did not disappoint in that regard. The headline in the Monthly Weather Report for November 1988 read:

“Generally sunny and dry; cold at night with frequent fog”

Figure 4 – Data courtesy of Wetterzentrale

Looking at the daily charts it’s easy to see why it was so foggy, and it was also the 10th driest November in the UK since 1910, and fourth sunniest since 1929. In the Review of Autumn 1988 in the Weather Magazine, R.A.S. Ratcliffe said when explaining about the upper air pattern across the northern hemisphere for November 1988:

On the 500 hPa monthly mean chart the circumpolar vortex was split, with part over Novaya Zemlya, and part over northern Canada. The jet stream was unusually strong in the eastern Pacific, but the most unusual anomalies of 500 hPa height were -140 m over western USSR, and +100 m over the UK.

I don’t have that particular 500 hPa level chart to hand, but I can generate the mean surface pressure anomaly chart for the month (fig 5).

Figure 5 – Data courtesy of NCEP reanalysis

July 2017 – why so mobile?

Figure 1 – data courtesy of NCEP Reanalysis.

July continues it a mood of being mobile and often quite cyclonic at times, in fact that’s how it’s been since the end of May across the British Isles, as this graph of zonality shows (fig 2). The simple answer  of why has it been so mobile is that mean pressure in the first three weeks of July 2017, has been 8 hPa below average across Baffin Island, and there has been a band of lower than average mean pressure extending westward across Iceland, before arching around Scandinavia and into eastern Russia. South of that the mean pressure across much of the central Atlantic has been higher than average (+3 hPa), and between the two the W’SW gradient has been tightened.

Figure 2 –  data courtesy of NCEP Reanalysis.

It’s very likely that this is all driven by temperature of the atmosphere at all levels. The SST is well below average around Baffin Island (-4°C), and the central mid Atlantic remains generally cooler than average (-1.5°C), although there is now a band of warmer water (+1.5°C) extending westward from America at ~38° north. It’s interesting to see the SST down the east coast of Greenland being colder than average, probably from fresh water from the summer melt of the glaciers.

Figure 3

This may help explain the very intense lows for July’s that we are seeing. Here’s the forecast for this Wednesday (26 July) from the Met Office, which shows an intense low of 973 hPa low at 19° west, throwing a frontal system across the British Isles. This low in turn, will spawn a series of secondary lows that will dumbbell around it before the week is out maintaining the mobility.

Figure 3

Finally, I thought that I would look at a virtual barograph that I would sit at 57.5° north and 22.5° west (where hopefully it won’t get too wet). As you can see (fig 4) the anomalies there have been mainly negative there for  long periods, and this is in an area of low pressure anyway and generally close to where the Icelandic low is found on mean pressure charts.

Figure 4

 

 

 

The unusual warm and anticyclonic spring of 1893

Figure 1

I noticed that the warmest spring* in the daily CET record back to 1772 in Central England was 1893. I don’t make a habit of looking for exceptional warm springs in the Victorian era, it was just that the spring of 1893 was even warmer than the spring of 2017 which has just ended (fig 1). The other thing that caught my eye was how exceptionally high the mean maximum was (anomaly +3.82°C), and how comparatively normal the mean minimum (anomaly +0.37°). This obviously points to a very anticyclonic regime back in the spring of 1893 to produce very warm days and comparatively cold nights, the graph below (fig 2) shows the contrasting anomalies during that spring perfectly.

Figure 2

So just how anticyclonic was it? A quick scan of the reanalysis charts for that spring reveals it was very anticyclonic.

Figure 3 – Courtesy of Wetterzentrale

Here are the headlines from the monthly weather reports compiled by the Met Office back then:

  • March 1893 Exceedingly fine and dry in all but the extreme north and northwest where showers were more frequent.
  • April 1893 Remarkably fine, warm and dry, especially over southern England where the severe drought continued with scarcely any intermission.
  • May 1893 Mostly fine and dry, especially in the south and east till mid-month, then unsettled with rain and thunderstorms in places.
  • June 1893 Generally fine and dry first half with local thunderstorms, the second half saw frequent showers and thunderstorms.

As you can see from the LWT analysis (fig 4), spring 1893 is easily the most anticyclonic in the series that started in 1871, with 58% of LWT being either anticyclonic or anticyclonic hybrid. It wasn’t cold, because the predominant flow was generally southeasterly or southerly rather that east or northeasterly. Spring 2017 is currently in 22nd position with a couple more days of records to go.

Figure 4 – Data courtesy of the CRU/UEA

It was also the second driest spring [MAM] since 1766 in England and Wales (fig 5).

Figure 5 – Data courtesy of the Met Office

*  I’m old-fashioned, and because of this I prefer to use seasons that start and end (approximately) at the times of the various equinoxes and solstices, so most of these stats are based on so-called ‘astronomical’ rather than ‘meteorological’ seasons.

May 2017 – mean MSLP and anomaly chart

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

You can understand why May ended up being the second mildest on record since 1910, when you see the mean pressure chart for the month (fig 1). There was a large negative anomaly (-13 hPa) in central Atlantic, which distorted the flow around a large elongated low of 1006 hPa (49N 30W), which pushed the Azores high further south than usual, producing a SSW flow over western Britain. Pressure over central Greenland was much higher than average (+15 hPa) pushing the normal Icelandic low south. The Greenland high ridged southeastward into Scandinavia and central Europe, with a mean northerly flow over much of that region.