Barometric pressure is rising so less rainfall – hopefully!

The sun made a return on Monday with 3.4 hours but due to a very brisk westerly wind, gusting to 35mph, the maximum of 12.7C was set mid-morning, which was 2.8C above the November average. However, just after 03.30 Tuesday morning the wind veered into the northwest and the thermometer fell away to a minimum 4.3C, still 0.6C above average. This brought to an end the run of mild nights with the lowest minimum temperature since 19th October.

Rain fell on Monday and also very heavy at 03.30 on Tuesday as a rain band passed through producing a daily total of 8.5mm.

As Tuesday dawned the thick cloud obscured the sky but just after sunrise the back edge of the weather front could be seem easing eastwards and the sun breaking through.

The barometric pressure has been rising rapidly with a current reading of 1015.5mb, the highest since 119th October, which means a more settled day or two with less rain and more sun. An intense high pressure, the current pressure is 1045mb, is centred to the south west of the UK and producing the north westerly run of air.

October 2020 Review

Record rainfall since weather station began in 1984

Storm Alex, named by Météo France on 1st October, was memorable for the three days of almost continuous rain that broke the record for the wettest day I have recorded since the station was set up in 1984. A total of 49.9mm fell on the 3rd that was preceded with 39.1mm on the 2nd. The previous wettest day occurred in May 2007 with 45.4mm. In fact I have only ever recorded seven days since 1984 when the daily rainfall has exceed 40mm. The deep depression eased across the English Channel and settled over the UK, slowly rotated and moved geographically, very little over the three days.

By the period 9th to the 11th a very different air mass covered the country. A deep depression to the east, rotating anticlockwise as they do, and a high pressure system to the west rotating clockwise, meant a run of Polar Maritime Air from the Arctic region. As a result temperatures by day and night were depressed being a couple of degrees below average. During the early hours of the 9th the thermometer fell to a minimum of just 2.9C, which was 4.2C below average. However, they were welcome dry days after the very wet days in the previous week.

The occurrence of extreme weather events somewhere in the world seems to be in the news more frequently. A new UN report involving 16 international agencies, coordinated by the World Meteorological Organisation, states that the world needs to raise investment in early warning systems for these extreme weather events calling for a change in emphasis from simply forecasting the weather to showing the impact of that weather system. Over the past 50 years recorded disasters have increased five-fold, thanks in part to climate change, they state. During that time period some 11,000 weather related disasters have claimed 2 million lives.

The recent examples are numerous but to name just four. Storms Ellen and Francis were two of the most notable August storms in the UK in the last 50 years, with gusts of 50 to 60kt in exposed coastal locations. The 3rd May was the wettest day on record in the UK. There have been record numbers of Atlantic hurricanes. In early October in southern France 500mm of rain fell in just 10 hours, which is equivalent to 60% of the annual UK rainfall in a few hours. Power supplier Scottish and Southern Electricity issued a warning of possible power cuts during the weekend of the 24th/25th as Storm Dennis was forecast to sweep across the Wiltshire area, fortunately the storm was less severe than predicted.

The World Metrological Office has stated that Hurricanes are getting stronger, moving more slowly over land and deviating further north and south of the equator. These can and do get caught up in the Jet Stream and bring very stormy weather to the UK.

My station began accurate recordings in 1984. Before the year 2000 I had never recorded daily rainfall in excess of 150mm during the month of October. Since that date there have been four years with daily rainfall in excess of 150mm in a twenty-four hour period being 2000, 2004, 2019 with 2020 totalling 191.0mm.

The Metrological Office lists nine severe weather UK weather events so far this year. Britain’s wettest day occurred on 5th December 2015 when 341.1mm was logged at the Honister Pass in Cumbria. January 2014 produced the wettest month in my records since 1984 with 219.1mm. Warmer air, resulting from climate change, holds more moisture so the trend of increasing rainfall on occasions is to be expected.

After four consecutive dry days with a cool northeasterly wind that meant below average temperatures during daylight hours, Sunday 18th was notable for a distinct change. During the course of a calm day, the maximum gust was only 7mph, the air mass began to arrive from a southerly direction from the Continent as a depression edged towards the country from the Atlantic.

There was all change on the 20th as Storm Barbara, named by the Spanish Meteorological Office, worked its way up the west of the country. It brought a Continental air stream that gave us the warmest day for a month with a peak of 16.7C being 2C above the average followed by a very mild night when the thermometer did not fall below 13.6C. However, this mild night was due to thick cloud associated with the depression that produced an extensive rain band and a very wet day on the 21st with 14.0mm.

There was a very mild end to the month as southwesterly winds brought warm, moist air across the country. A significant diurnal range (temperature difference between day and night) of just 0.5C occurred during the 29th/30th with a maximum of 13.9C and minimum of 13.4C. The final day of the month was wet and windy as Storm Aidan, named by Met Éireann, advanced to the northwest of Ireland, with gusts to 36mph on the 31st.

The additional rainfall of 11.1mm on the 31st brought the October total to 191.0mm.This rainfall total of 191.0mm was a record for my station set up in 1984 breaking the previous high of 159.3mm in 2004. The average number of wet days (rainfall equal to or greater than 1mm) in October is 12 but this past month saw 22 wet days and only 7 dry days. The rainfall total for the ten months of January to October was 828.3mm being 163mm above the 36-year average.

With the sunshine total some 14 hours below average it was not surprising to find the mean temperature was 0.3C below average. The extensive cloud cover meant the average maximum was 0.6C below average, however, it provided a duvet during many nights that meant an absence of frosts with the average minimum exactly average.