July 2016 circulation

I know it’s not quite the end of July [2016], but I thought I would produce anomaly charts for mean sea level pressure [MSLP] so far this month, and see what influence the atmospheric circulation may have had on rainfall in parts of the south and east England. Quite a simple anomaly chart in truth, up to the 24th of the month there was a belt of lower than average pressure over the central Atlantic (-4 hPa) and higher than average pressure over Greenland (+7 hPa) and central Europe (+3 hPa).  The British Isles is sandwiched between the two, with the zero anomaly running WSW-ENE across northern England with higher than average pressure to the south and lower than average to the north. The belt of anomalous low pressure in the central Atlantic ties in nicely with the lower than average sea surface temperatures [SST] in the central Atlantic. This kind of flow would have produced rather cloudy weather in the north albeit rather warm and muggy at times, the closeness of the high pressure ridge over central France would also would explain the low rainfall totals in the south.  This might be a slightly better explanation than the “random distribution of showers” that Matt Taylor proffered on twitter as the reason, but I’ll leave it to you to be the final arbiter on that.

Mean Sea Level Pressure Anomalies 1 Jul - 24 Jul 2016

Mean Sea Level Pressure Anomalies 1 Jul – 24 Jul 2016

Mean Sea Level Pressure 1 Jul - 24 Jul 2016

Mean Sea Level Pressure 1 Jul – 24 Jul 2016

Mean Sea Level Pressure Anomalies  1 Jul - 24 Jul 2016

Mean Sea Level Pressure Anomalies 1 Jul – 24 Jul 2016

Mean Sea Level Pressure  1 Jul - 24 Jul 2016

Mean Sea Level Pressure 1 Jul – 24 Jul 2016

Kelvin-Helmholtz effect in central Pacific…

North Atlantic SST Anomalies on 20 July 2016

North Atlantic SST Anomalies on 20 July 2016

The cooler water in the central Atlantic persists, not because it’s that’s cool more because it’s surrounded by warm waters to the north, east and now west. The southwest approaches and Biscay both have positive anomalous Sea Surface Temperatures [SST] of +2°C, although curiously the SST’s in the English Channel south of the Isle of Wight are near average.  If you look back to as recently as early May these anomalies did not exist. Massive areas of warmer than average SST north of Iceland and west of Svalbard persist with anomalies as high as +4°C – will that area ever see sea ice again? In comparison the Mediterranean looks quite normal. I’m just wondering what these latest SST values spell out for the coming Autumn and Winter.

There’s some kind of Kelvin-Helmholtz effect going on in the central Pacific, and I mean in the SST anomalies and not in the sky, as the last vestiges of the recent El Nino collapses to make way for a La Nina event that will start later this year perhaps. These pulses of cold and warm SST anomalies are definitely very fractal like, and I’m sure there is probably an explanation to this effect, but you won’t get it from this blog unless someone kindly posts us the answer in a comment!

Central Pacific SST Anomalies on 20 July 2016

Central Pacific SST Anomalies on 20 July 2016

July 2016 – Latest Polar Sea Ice

I was looking at the latest sea ice figures yesterday and noticed that in the Arctic 2016 had closed the gap since the start of June on the year 2012 by a large amount, so much in fact that for the 14th of July, 2016 has now slipped to the third lowest sea ice extent (82.3% of the LTA for this day of the year) behind both 2011 and 2012. If 2016 is to set up a new minimum this year, then it has to keep up a fair old rate of loss even just to keep up with 2012. In May I thought that 2016 would be a racing cert to set up a new minimum Arctic ice extent , but at the moment its neck and neck with 2012.

Latest Arctic Sea Ice (14 Jul)

Latest Arctic Sea Ice (14 Jul)

Meanwhile in the Antarctic, the sea ice extent is steadily tracking the long-term daily average at the moment, but still -4.2% down on last year.

Latest Antarctic Sea Ice (14 Jul)

Latest Antarctic Sea Ice (14 Jul)

Very wet in northern areas; warmer and thundery in the south…

Lamb Weather Types for 27 Jun 2016 - 22 Apr 2016

Lamb Weather Types for 27 Jun 2016 – 22 Apr 2016

Very wet in northern area; warmer and thundery in the south” that’s how the monthly weather report from the Met Office summed up July 1985. The reason that I mention this is that I’ve had a look at the objective Lamb Weather Types [LWT] that I download from the Climate Research Unit [CRU] at the University of East Anglia. I then ran a very simple compare routine to find the best match from LWT for the period 31st of May to the 27th of June for 2016 in all previous years back to 1871. And top of the list came 1985, whether this has any significance in what the weather for the next month in the UK will be like I’ll leave you to judge – at the end of July! All I can say is that there are a remarkable number of high place analogs for June 2016 so far, a month that was anticyclonic until the 9th, and then became more and more progressive and occasionally cyclonic as the month went on. I’ll freely admit I did run this same analysis (but looking at 7 days rather than 28) at the beginning of the month and found that 2009 (the barbecue summer),  was almost a perfect analog for the first week of June 2016.  In this latest analysis, 2009 is a 73.4% match for 2016, whilst 1985 is a 90.2% match, again I will stress the analysis is very simple and a little bit of fun. When you publish a blog you must have the courage of your convictions and on the strength of the summer so far, often cyclonic and thundery, and looking at the latest T+192 of the GFS, I might be off to a bit of a flyer!

Lamb Weather Type Analog for the Last 28 days [31 May - 27 Jun] Match Average Indices method

Lamb Weather Type Analog for the Last 28 days [31 May – 27 Jun] Match Average Indices method

North Atlantic MSLP & 500 gh [WZ] July 1985 (courtesy of Wetterzentrale)

North Atlantic MSLP & 500 gh [WZ] July 1985 (courtesy of Wetterzentrale)