August 2016 circulation

Mean Sea Level Pressure Anomalies 1 Aug - 31 Aug 2016

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

Mean Sea Level Pressure 1 Aug – 31 Aug 2016

August Temperatures

Air Temperature Anomalies 01 Aug to 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).

Warmest August since 2004 in Central England

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):-

Daily Central England Temperatures August 1772 - 2016

I make it the 27th warmest August since 1659 judging by its monthly mean temperature:-

August mean CET & anomaly

August mean CET & anomaly

Yesterday’s rain fails to halt the drought

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

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.

rainBelow 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

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!