8/9 November 2016 – trough disruption

The trough disruption that occurred yesterday across the British Isles was well forecast by both the GFS and UKMO models, here are a couple of animations in hourly time steps of it happening. The warm air quickly occluded out as it came up against the cold air over Scotland and northern England and a secondary low formed on the triple point as the pressure continued to fall. This low tracked ESE across Wales and southern England with strong winds on its SW flank and behind the cold front.

1000-0900-on-9-nov-2016

Further north snow fell quite widely east of the Pennines even to low levels.

1000-0800-on-9-nov-2016

estimated-rainfall-accumulations-1200-1010-utc-on-wed-9-november-2016

The exceptional warm start to September

If you think that we’ve had in warm here in the UK during the first 14 days of September then it’s been very much warmer over central Europe with anomalies as high as +6°C. I  just wonder if the extreme warm anomalies that occurred over Russia during August, which were as high as +8°C for the entire month, have somehow retrogressed and migrated westwards.

air-temperature-anomaly-01-sep-to-14-sep-2016

The pressure patterns gives us the reason. The Icelandic low is misplaced, a little further southwest and 11 hPa deeper than usual, whilst a belt of high pressure stretched from the Azores to Poland with pressure anomalies of +4 in the southern Baltic Sea. This produced a conveyor belt of tropical maritime southwesterly for most of northwest Europe, but sunny, very warm or hot anticyclonic conditions for much of central Europe.

mean-sea-level-pressure-1-sep-14-sep-2016 mean-sea-level-pressure-anomalies-1-sep-14-sep-2016

 

 

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

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