Author: Eric Gilbert

The very cold air streaming down from the Arctic on Monday meant a cold day with the temperature not getting above 8.2C, which was 6.1C below the April average. However, that was only part of the story as the strong wind, gusting to 24mph, meant there was significant wind chill that for most of the day it felt at least 2C colder outside than indicated on the thermometer.

A band of light precipitation crossed the area at 11.40 and ice pellets were observed. It was not fluffy snowflakes as what fell from the sky was very much smaller than hail and much more irregular and bounced as it hit the ground. Being small and light it was blown around in the wind and could have been mistaken for small snowflakes. Ice pellets form when snowflakes start to melt as they drop from the cloud, then fall through sub-freezing air, whereby they refreeze into grain-like particles.

The thermometer dropped below zero at 22.41 Monday evening and continued downwards unit 07.20 on Tuesday. This produced another hard frost with a minimum of -2.8C at 05.00 on Tuesday. This low was 4.9C below the 37-year average.

Much blue sky and sunshine was in evidence after dawn on Tuesday but shortly after 08.00 cloud began to drift across obscuring much of the sun. By that time the thermometer had recovered to 1.6C. The anticyclone has drifted a little further south so the wind has backed a few degrees and currently coming from the north-northwest. The very dry air continues with humidity at 08.00 as low as 73%.

Sunday was a gorgeous day with 9.8 hours of glorious sunshine and in the afternoon the thermometer rose to 15.9C being 1.6C above the 37-year average.

Overnight and during the early hours two cold fronts traversed the area with the wind veering from the west and then northwest into the north. The second cold front passed over southern England at dawn with thick cloud and very light drizzle that was not measurable but recorded as a ‘Trace’.

Monday morning after 08.00 saw the cloud thinning and rising as the weather front continued southward. By this time the thermometer had fallen away to its lowest point with a minimum of 5.2C. The humidity on the northerly wind is exceptionally dry with a reading of 67% at 08.00. The last time the humidity at this time of day was so low was on the 9th July 2019 with 69%.

The effect of the north easterly winds, still in existence on Saturday, can be be seen in the slow fall of the maximum temperatures for the past five days with 22.1C, 18.9C, 13.6C, 10.3C and 9.2C on Saturday. The peak on Saturday was 5.1C below the 37-year average and the coldest day since 7th March.

The continued loss of warmth has occurred before the Arctic blast arrives on Monday.

Overnight, under clear skies and with the wind having dropped out, the thermometer dropped to -3.3C at 06.43 on Sunday producing a hard frost.

The start to Sunday was glorious with sunshine as soon as the sun rose above the eastern horizon so that by 0800 the thermometer had risen above freezing with a temperature of 0.2C. The soil temperature at a depth of 5cm has dropped from 9.1C on the 1st to 1.7C on Sunday.

The anticyclone that has been resident over the North Atlantic for the past four days is losing central pressure and slipping southwards so that on Sunday the air mass will, for most of the day, come from the west.

The persistent wind from the north east on Friday brought another cool day and colder than Thursday. The thermometer struggled to reach a maximum of 10.3C, which was 4C below the average for April and down 3C on the Thursday peak. Wind chill as a result of the strong cool wind, gusting to 26mph, meant it felt at least 1C cooler outside due to wind chill.

It was another dry day with 8 hours of welcome sunshine and the UV level back into the ‘Moderate’ level.

The air from this direction continues to be very dry dropping to 46% during Friday.

The past night was again chilly with a minimum of 2.7C at 04.19 on Saturday that was 1.9C below average.

Saturday arrived with total thick cloud cover with little solar energy percolating through, currently little chance of seeing the sun. The thermometer rose to 4.6C at 08.00 but wind chill meant it felt more like 2.8C outside at that time.

The north easterly wind onThursday, a cold direction, limited the warmth of recent days with a maximum of only 13.6C, which was 0.7C below average. The wind was strong, gusting to 27mph, that meant wind chill was a factor so that it often felt at least 1C below that indicated on the thermometer.

Sunshine was also reduced with only five hours and the UV level, due to high cloud, reached a peak of only 2.7, which was at the top end of ‘Low’.

Thick cloud greeted Friday morning with the northeasterly still gusting strongly after a minimum temperature of 2.9C at 05.12 being 1.2C below average. By 08.00 The thermometer had risen to 4.1C but wind chill meant outside it felt more like 2.8C.

The anticyclone is intensifying and moving very little at the present time that means the wind will continue to come from this cold direction and very brisk with a gust of 23mph recently.

March 2021 Review

March began with persistent winds from the northeast that meant temperatures were depressed. Thick cloud carried in overnight from the North Sea blanketed the area that on one morning limited visibility to 200m. On the 4th the thermometer struggle to reach just 4.4C, which was 6C below the 37-year average.

There followed several nights when an air frost occurred, the coldest being in the early hours of the 8th with a minimum of -3.3C being 5.7C below the long-term average. However, just after dawn the temperature had risen to 0.7C with no evidence that a hard frost had occurred.

The wind direction changed significantly from the 8th backing into the west and then south as the anticyclone eased away and a depression approached from the Atlantic driven on by a strong jet stream. A peak gust of 42mph was recorded in the early hours of the 11th.

The succession of weather fronts during this period gave us three days of rain with the wettest on the 12th with 8.5mm.

A welcome anticyclone approached on the 13th and intensified over the UK for ten days reaching a peak pressure of 1035.8mb. This brought fine weather and minimal rain with daytime temperatures above average but due to clearing skies many cool nights.

Several rain bands crossed the country on the 25th and 26th adding another 8.3mm on the latter day, the second wettest day in what proved to be a relatively dry month.

The month ended with a flow of Continental Air on a southerly air stream that arrived from North Africa and Iberia. The 30th saw the thermometer soar to a maximum of 22.1C, which was 11.6C above my 37-year average and a record for this station set up in 1984. I understand that it was the warmest March day since 1968. The 30th didn’t reach such heights but a peak of 18.9C was the second warmest for March.

Overall March gave a mean temperature 0.4C above average that was principally due to the last three days of unusual warmth. By contrast, we had 6 nights when an air frost occurred with -3.3C during the early hours of the 8th the coldest.

March 2021 was a relatively dry month with only 36.6mm of precipitation recorded. The total was 23.2mm below the 37-year average and the driest match since 2015 that followed a below average total for February. There were 20 totally dry days when the long-term average is 16.

Although it was an above average month for temperature it was not thanks to many hours of sunshine as the solar energy total was only 82% of the 12-year average. The UV level reached a ‘Moderate’ level on just 6 days.

It is interesting to analyze the diurnal temperature range for March since 1984 when I find that in the latter 1980’s the average was 15C but recent years have seen the average range increase to 17.5C. On the 30th our human frame had to adjust to a diurnal range of 22.5C.

I came across an interesting item recently, having commented in a recent monthly review about the importance of accurate data when monitoring the oceans with regard to CO2 and the rise in sea level. A new era of sailing for science began in January with support for vital ocean observations from the high-profile round-the-world Vendée Globe yacht race. Ten of the skippers took with them scientific instruments including either drifting buoys that gather climatological information or Argo floats that analyse seawater. During the race they deployed all the drifting buoys and almost all the Argo floats at agreed co-ordinates in the Atlantic. The World Meteorological organization stated recently that “We cannot stress enough the importance of the oceans, without them there would be no life on earth. As major players in our climate system, they store over 90% of the excess heat from radiative forcing and absorb about a quarter of the human-produced CO2 emitted annually”.

Seven meteorological buoys and 3 profiling floats, operated respectively by Météo-France and Argo France, were deployed by the IMOCA skippers at agreed positions in the Atlantic Ocean.  Four skippers also carried onboard equipment to measure essential ocean variables such as sea surface salinity, temperature, CO2, atmospheric pressure, as well measure the microplastics pollution at sea. The article concluded that “usually, the deployment of ocean observing instruments is done through research oceanographic ships, which are very costly and not able to sail everywhere throughout the ocean regardless of the season. Racing yachts can reach remote and not yet well sampled areas of the ocean, filling critical observational gap”.