Latest Arctic sea ice – 7 Sep 2016
It’s not quite reached the minimum sea ice extent in the Arctic but it’s close. The average date for the Arctic minimum is in fact the 11th of September as far as I can see, and looking at the latest figures up until the 7th of September that’s still in doubt, especially as the minima could still occur as late as the 21st (as it did in 1989) which could mean a further two weeks of decline.
Arctic sea ice extent minima 1978-2016
Meanwhile 180° south, the Antarctic sea ice is reaching its peak, which if my programming is correct is still 12 days short of the average data maxima occurs on the 19th of September. The increase in sea ice has taken quite a knock in the last 10 days, and at the moment the 2016 maximum has dropped to the 22nd highest since 1979.
Latest Antarctic sea ice 7 Sep 2016
Antarctic sea ice extent maxima 1978-2016
Looking at the bigger picture and the rolling 365 day mean since 1989 it’s clear that as the Arctic sea ice has dropped by 14.1% in those 27 years whilst at the same time the Antarctic sea ice has increased by 7.6%, although in the last year that increase has slowed quickly.
Mean Sea Level Pressure Anomalies 1 Aug – 31 Aug 2016
Lower than average pressure across the central Atlantic (-3 hPa) and higher than average pressure across central Europe (+5 hPa); with even higher anomalies over Asia (+8 hPa); meant that there was a W’SW flow across the central Atlantic and the British Isles in the mean pressure chart for August, this flow extended across the North Sea and into northern Germany, Poland and north and west Russia. You would have thought with that kind of pattern that there would have been more rain across the British Isles than there was, but mean pressures of around 1019 hPa across the south must have warded off most of that.
Mean Sea Level Pressure 1 Aug – 31 Aug 2016
Air Temperature Anomalies 01 Aug to 31 Aug 2016
I must admit that I never realised just how warm it had been over central Russia in August, a monthly anomaly of +8°C is something quite special. Other than that their were negative temperature anomalies over the Balkans (-2), Scandinavia (-1), North Africa (-1) and of course the central Atlantic(-1).
Synops 1500 UTC on Sat, 3 Sep 2016
A low pressure was deepening and tracking into Western Ireland on this plotted chart for 1500 UTC on the 3rd of September, its associated warm front had crossed all of Wales, and was lying approximately from Llandudno to the Isle of Wight by 1500 UTC.
Estimated Rainfall Accumulations 0600 – 0600 UTC on Sun, 4 September 2016
Above is a map of estimated rainfall totals gleaned from 15 minute weather radar images from the Met Office between 0600 on the 3rd and 0600 UTC on the 4th of September. The wettest places were over South Wales with totals in excess of 50 mm in the 24 hours. For some reason the 21.3 mm estimated total at Carlisle was considerably less than the gauge total of 36.8 mm. Here’s the frame for 0245 UTC on the 4th:
Who knows if more frequent and higher resolution images might have improved that? It’s on a knife-edge here with very high intensities just to the south of Carlisle, and I just wonder if my mapping projection conversion code might be very slightly out particularly when calculating latitudes, I’ll revisit the code, but it’s the kind of code that you don’t ever want to see again.
Daily 24 hour rainfall [06-06] 3 September – Sunday, 4 September 2016 In WMO Block 03 Highest Daily Rainfall [06-06]
There were reports on social media of flooding at Braunton in North Devon. I estimate that the 24 hour total at Braunton was around 16.6 mm in the 24 hour period, so not a large total, but looking at the (inset) intensity graph a lot of it came in a very short time during the afternoon, and with the ground being baked dry from several months of dry weather there must have been a great deal of runoff that might have contributed to the local flooding.
Estimated Rainfall Accumulations 0600 – 0600 UTC on Sun, 4 September 2016
I have just downloaded the gridded 1910 data series from the Met Office for August so that I can have a look at the 2016 summer index across the country. I require that sunshine, rainfall and temperature gridded data so I can calculate the monthly terciles and quintiles values that are used to calculate the summer index. The summer is of course the meteorological summer and consists of the months June, July and August. The table below is the summer index for the whole of the UK, and as you can see summer 2016 index was +10 which is above average and much better than last year, but comes only joint 19th best since 1929.
UK Summer [JJA] Index 1929 – 2016
The picture is much better when you look at the regional summer indices that I’ve also calculated and ranked. East Anglia comes top with an index of +25 just ahead of southern England with +20. Incidentally, in East Anglia summer 2016 was also the best summer index since 1995. No region in Scotland fared particularly well this summer with summer indices of around average (remember the best summer scores 48 and the worst summer -48 using the summer index formulae). You can find more details about the summer index in an earlier article I wrote earlier this year.
Best Summer Index [JJA] in 2016
Daily CET Summer [JJA] 2016
It looks like Summer 2016 was the warmest in Central England since 2006 with a mean temperature of 16.43°C which was +1.08°C above the long-term average (1961-1990). Surprisingly no maximum records were broken during the summer but two high minima were.
Warmest Summers 1659-2016
In the bigger scheme of things Summer 2016 was the joint 27th warmest since 1659 based on mean temperature.
Summer mean CET & anomaly 1659 – 2016
August 2016 looks like it was the warmest since 2004 with a mean CET of 17.12°C which was +1.38°C above the long-term average (1961-1990):-
I make it the 27th warmest August since 1659 judging by its monthly mean temperature:-
August mean CET & anomaly
I got a little fed up with hearing every BBC weather presenter churn out the phrase “this are of low pressure is very unusual for the time of year” and decided to investigate the truth of the matter. Of course, it all depends on what you term “unusual”, I know personally that as I get older how easy it is to forget past events, and that the low now tracking into Ireland might not be that unusual at all, and that’s when gridded MSLP data and weather statistics drawn from that data come into their own.
I’ve used the NCEP reanalysis six hourly MSLP data back to 1948 to find the extreme mean sea level pressure [MSLP] range for August. I decided to look at a grid size that extended from 10W to 2.5E and from 50N to 60N a total of 30 grid points in total. I could go back farther but the grid size changes to a 2°x 2° grid from the 2.5° x 2.5° later grid and I need to write the code! There is one problem in the analysis in that it’s looking for a minimum pressure in the grid around the British Isles which won’t necessarily find a discrete low pressure circulation, but until I write an algorithm to do that with this will have to do.
Extreme MSLP August – British Isles [50N-60N 10W-2.5E] 1948 – 2016
As you can see the lowest MSLP in August in the vicinity of the British Isles was 972.3 hPa on the 24th August 2005, the one that’s affecting us at the moment is off the west coast of Ireland with a central MSLP of around 980 hPa and filling. Admittedly the lowest pressure then was just to the northwest of Scotland.
Extreme MSLP in August across the British Isles [1948-2016]
Here are just few of examples from the list of extreme low pressure systems across the British Isles that you may remember from the past.
Synops for Tue, 26 Aug 1986 at 0600 UTC
Hard to say but the centre of this low over northern Scotland looks around 970 hPa on 30 August 1992.
Synops for Sun, 30 Aug 1992 at 1800 UTC
This is the infamous low ‘Y’ that wreaked havoc in the Fastnet race in 1979.
Synops for Tue, 14 Aug 1979 at 1200 UTC
The Met Office have just issued their usual mid month report on the weather and say this about rainfall in the first half of August 2016:
“After the first day of the month, when an area of low pressure gave some large rainfall totals in the south, England, Wales and Northern Ireland have been much drier than average. By this stage in the month you would normally expect around 52% of the total month’s average to have fallen. However, many parts have seen less than 20%, with Anglesey only recording 5.6mm which is just 7% of the total month average”
Courtesy of the Met Office
This is a perfect example of how statistics in an anomaly map don’t always give you the full picture. I am not saying that the anomalies are wrong, they aren’t, but the anomalies are masking the fact that as in July, August at a good many stations across the south of England was a drought. So at first glance you would not know that the south although wetter than parts of Eastern England, had suffered a drought. There are a number of ways a meteorological drought can be defined, but I like the one that says 15 consecutive days with less than 0.2 mm of precipitation in any day. Even yesterday’s rainfall has failed to halt the drought in quite a number of locations across the south of England as you can see from the following map of ‘days of drought’ gleaned from the SYNOP observations.
Below is a tabulated list of stations and the number of days of drought, and as you can, there are at least seven stations that have gone 15 days with less than 0.2 mm in any day, yesterday there were many more with 14 consecutive dry days. Tomorrow’s rain will put paid to this very short-lived drought I’ve no doubt.
Estimated Accumulated Precipitation 00 UTC on 1 August 2016 – 12 UTC on 18 August 2016 WMO Block 03
Please note that because the Irish stations don’t report a 24 hour total I calculate the above rainfall stats using a 00-00 UTC daily total, so the number of drought days at Bournemouth of 15 is based on this, but if you use the 06-06 (24 hour) total the drought ended yesterday. Rainfall statistics gleaned from SYNOPs are not at all straightforward!
Someone on the Weather and Climate Google Group asked me to produce a list of the 50 warmest daily anomalies in the Central England Temperature [CET] series in a similar manner to how I produced a list of the 50 hottest days since 1878, and so here it is!
50 warmest daily CET anomalies since 1878
So there were nine entries in the top fifty that have occurred since 2001, but surprisingly to me, an April was in top spot, the 3rd of April 1946 to be precise, with an anomaly of +13.6°C for that day, closely followed by the 3rd July 1976 (+13.2) and the 9th of August 2003 (+12.8). This is the chart of the 3 April 1946 courtesy of Wetterzentrale, so obviously a very warm spring day in an anticyclonic SE’ly.
Also noticeable was the 29th of March 1965, with a remarkable range in anomalies of -2.2°C minimum to +11.5°C maximum. The actual temperature range was 21.5°C from a minimum of +0.7°C to a maximum of 22.2°C in the day.
Warmest Central England Temperatures for the 29 March