Cold front brings change overnight Plus November Review

Monday was another gloomy day under thick, low cloud without any sunshine that saw the thermometer rise to 9.7C, just below average for November. There was a little light rain late afternoon and again at 21.00 as the very narrow cold front passed through bringing 0.3mm of rainfall. The monthly rainfall total rose to 71.2mm

As the cold front passed through the temperature slowly fell away to a minimum of 2.1C at 07.27 on Tuesday with evidence of a ground frost.

Tuesday after dawn brought variable, high cloud.

November 2020 Review.

A mild and moist month

The new month arrived with unsettled weather from the tail end of Ex hurricane Zeta crossing the country. The wind gusted to 38mph on the 1st with 5.9mm of rainfall and then 8.5mm on the 2nd. During the first two days of November the warmest day of the month was set producing a maximum of 15.5C, which was 5.5C above average and the warmest night of the month when the thermometer did not sink below 11.8C being 8.1C above average.

On the 3rd a huge buckle occurred in the jet stream allowing the influence of an intense high pressure system in the North Atlantic to bring fine, sunny and dry weather for five days. After so many dull, wet and sunless days it was a pleasure to have several hours of sunshine with light winds, a maximum gust of just 9mph on the 4th. However, the clear skies at night allowed the thermometer to fall low with ground frosts on two nights, the coldest being -1.7C in the early hours of the 4th. Fog also formed in the early hours of the 5th and 6th limiting visibility to 200m.

The second week saw a succession of depressions advance from the Atlantic that combined with high pressure over Germany brought a flow of mild, moist air from Iberia that meant several days with above average maxima. The wettest day of the month occurred on the 20th with daily rainfall of 26.1mm making it the wettest day since 3rd October

On the 10th a sub tropical storm developed in mid-Atlantic that broke the record for the number of storms in 2020. Storm Theta was the 29th such storm to form, however, it drifted north-eastwards towards Madeira rather than the usual course towards the Caribbean. The 30th storm, that far exceeded the record set in 2005 for Atlantic storms, was Storm Iota that formed on the 14th, which wreaked havoc over Central America for several days with sustained winds of 155mph.

The middle of the month saw south-westerly winds persist with modest rainfall amounts but as the 20th approached high pressure built up and was in residence for several days bringing much calmer weather but allowing a light air frost under clear skies that saw the thermometer drop to -0.4C on the 23rd.

The global mean sea level has risen about 21–24 centimetres since 1880, according to the National Oceanic and Atmospheric Administration, with about a third of that coming in just the last two and a half decades. They state “As global temperatures rise, melting glaciers and ice sheets have combined with the thermal expansion of seawater to increase sea levels at an alarming rate”. Marlborough is far from the coast so will not experience any flooding from this phenomenon but low lying coastal areas could be devastated in the future as sea levels are forecast to continue rising. Oceans absorb about 90% of the excess heat trapped by greenhouse gases, which contributes to sea level rise. Currently a flotilla of autonomous floats, that have covered the seas since the early 2000’s, bob down as low as 2,000 meters every day to capture data at a depth. Research is under way to utilise these floats to accurately ascertain sea-level rise. Sound travels faster in water when it is warmer therefore differences in speed of sound can reveal the change in water temperature.

In addition, the Sentinel-6A satellite was launched on the 21st to also monitor sea levels that will provide “unprecedented accuracy”. It carries a radar altimeter, which measures the time it takes for radar pulses to travel to Earth’s surface and back again. A sister satellite will be launched in another five years to support these measurements.

The anticyclone eased away on the 24th allowing southerly winds to bring mild, moist air from Iberia over the country again with light rain showers and above average temperatures. At that point in the month we had only experienced one day with a below average maximum temperature.

The month finished with five days of below average temperatures with the coldest day of the month on the 27th when the thermometer struggled to reach 5.4C making it the coldest day since 5th March. That night a hard frost set in when the minimum fell away to -3.7C being 7.4C below average and the coldest night in 2020 equalling that recorded on 21st January.

November has been a relatively warm month with the mean temperature 1.2C above average making it the warmest since 2015. Analysing the data the mean daytime and nighttime extremes were 1.5C and 1.0C above average.

It has seemed a damp month with numerous days of rain and recently morning fog. A large proportion of the monthly rainfall, totalling 71.2mm, fell on the 14th when 26.1mm was recorded. The monthly total was 77% of the 36-year average or 21mm below.

Fog was observed during the early hours of eight days and an air frost recorded on seven mornings.

Autumn 2020 was a mild season with the mean temperature 0.3C above average and rainfall of 292mm being 51mm above average.

Mist and murk persist

Sunday was another day that started and ended with fog. The air was very still underneath the large area of high pressure. For many hours the anemometer hardly moved and was stationery after midnight with a peak gust of just 10mph in the morning. The cloud was so thick and dense that no solar of UV registered on the instruments.

It was another dry day, the twelfth this month with rainfall total of 70.9mm when the average is 92.3mm.

The thermometer struggled to reach a peak 6.5C during daylight hours, which was 3.5C below average and fell away to 3.1C at 02.52 on Monday morning.

Monday saw little change after first light with fog again limiting visibility to 300m and the anemometer stationery.

Although there was little breeze over the past twenty-four hours the air mass initially came from the northeast but during the day there was a slow but subtle shift into the north and then northwest before late evening coming from the west.

Anticyclonic gloom pervaded Saturday

Saturday arrived with fog that limited visibility to 200m and only slightly improved as the day wore on. We were, and still are on Sunday, under an extensive area of high pressure that still stretches from mid-Atlantic to Scandinavia. There was very little wind to stir up the atmosphere with a maximum gust of 11mph but for most of the day the anemometer was still or rotated very slowly.

The thermometer rose just over 1C during daylight hours to reach a maximum of 8.8C being 1.2C below average. The minimum of 5.0C was logged just after midnight.

Our large 16 solar panel array, that at this time of year can produce almost 3kw, struggled to produce 100w for most of the day with one very brief rise to 240w at 11.45.

Sunday after dawn saw that little had changed in our weather with fog still in evidence from the low, dense cloud that limited visibility to 300m. By 09.00 the fog had thickened to limit visibility to less than 200m.

Coldest day in eight months

After the coldest night since January, Friday during daylight hours, brought us the coldest day since 5th March as after the hard frost the thermometer struggled to reach 5.4C at 13.46. However, we were not encased in fog that was close to the north, and occasionally crept over the Marlborough Downs towards Marlborough but not reached, as we enjoyed 3.4 hours of sunshine in the morning that faded away after 13.00. The temperature dipped to 3.3C late afternoon at 16.00 before recovering overnight to reach 7.1C at 08.00 on Saturday. The wind on Friday was from the northeast but a subtle change late in the afternoon on Friday saw it veer into the east allowing slightly warmer and moist air to arrive.

A fragmented band of rain crossed the area during the early hours of Saturday producing 0.7mm of rain that triggered the rain gauge at 04.45.

Saturday dawned with fog that limited visibility at first to 200m. I suspect that the fog is due more to a very low cloud base than the moist air travelling over the cold ground condensing in the almost still air.

Coldest night in 2020

The ridge of high pressure brought a fine day on Thursday, after a cloudy start, but the air mass, very calm with a maximum gust of just 7mph, was from the north-northeast. As a result of the cooler air the thermometer struggled to reach 8.4C at 14.06 during the 3 hours of sunshine, which was 1.6C below average. It was the coldest day since 28th April.

As the afternoon moved into the evening the thermometer slowly fell away and reached -0.1C at 19.32 when an air frost began to develop. The minimum reached at 08.05 on Friday morning was -3.7C. This made it the coldest night in 2020 and equalled the minimum on 21st January 2020 being 7.4C below the 36-year average.

Fog formed in the early hours, after a misty evening, that limited visibility to 400m at dawn on Friday but slowly evaporated so that by 08.40 visibility had increased to 1200m as the sun began to rise bringing weak sunshine. The high pressure is still dominant so another fine day is in prospect.