Author: Eric Gilbert

There were many hours of sunshine on Wednesday but a couple of very light showers occurred mid-morning that amounted to 0.3mm but nothing thereafter. The wind was very strong during daylight hours, peaking at 30mph again in the afternoon. The thermometer eventually peaked at 14.4C, logged at 14.41, being just 0.3C above average. As the skies cleared in the evening the thermometer began a steady fall reaching a low of -1.5C at 05.44. Analysing the minute by minute data stream the air frost began at 02.55 and only returned above freezing at 06.58, thus four hours of freezing air. Thankfully, my apple blossom is yet to unfurl, so no damage last night.

After dawn on Thursday the sun began to work lifting the temperature to 4.4C by 08.00, however, it was the coolest start to a day at that time since the 10th (4.1C). The wind will be much lighter today, changing direction from an easterly quadrant first thing to a south-southwest air flow this evening.

We are now under the influence of another major depression, centred in the western approaches, so the unstable weather pattern continues with sunshine and the likelihood of showers occurring. There is the possibility of fair weather clouds, cumulous clouds, occurring again today. As the warmth increases the moist air rises, condensing into white, puffy clouds.

This depression will, as yesterday, move northwards up the western side of the UK, principally later today and on Good Friday, so once again we are likely to be on the periphery of any substantial rainfall.

After a relatively calm and sunny day on Tuesday the thermometer lifted above average again, just, with a maximum of 14.7C being 0.6C above my long-term average. Thicker cloud built up in the afternoon, thanks to the depression that had been lurking over Brittany, throwing up a large area of cloud that produced light rain just after 16.00. Another light rain shower triggered the automatic rain gauge at 00.52 that raised the daily precipitation to just 1.0mm. Considerable rain ran up the east and west coasts during the day and to the west overnight. The low of 4.6C was logged at 05.59 early Wednesday being also above average, just, at +0.9C.

Wednesday after dawn revealed broken cloud scudding fast across the sky. Overnight, the depression had decided to move north and visit the UK, continuing to move north to the west of our region. We have been, and continue to be on the periphery of the depression, however, the wind strength increased markedly during the late evening and overnight as we were close to the centre of the depression. The minimum barometric pressure of 994.1mb was logged, the lowest since 28th January. The first indication of rising wind strength was observed just after 22.00, building to a peak of 33mph at 02.14, but close to that peak for several hours. As the day progresses the cloud is likely to break up and thin as the depression eases away, allowing some variable sunshine with the wind slowly decreasing.

The temperature of 6.7C at 08.30 felt more like 5.0C outside due to considerable wind chill. Wind chill could be called the ‘feels like’ temperature being different to the actual air temperature, which measures air temperature, relative humidity and wind strength at five feet (human height) as well as an understanding of how heat is lost from the human body during cold and windy days.

There is no official definition of wind chill as definitions vary globally, dependent on how it is measured. In the UK, a system called the Joint Action Group for Temperature Indices is used to realistically measure wind chill. This calculates wind chill by measuring how much heat is lost from a person’s bare face at a walking speed of 3mph.

As the depression moves away the barometric pressure is rising rapidly at over 4mb every three hours.

Although the wind was predominantly from the warmer southwest during daylight hours on Monday the variable cloud and limited sunshine restricted the temperature rise to a maximum of 13.5C at 12.56 being the first below average peak this month at -0.6C.

The first spots of rain, only spots on the window, were observed at 19.30 as the main rain band progressed up the western side of the country leaving us on the fringe of a wide rain band. There were a couple of brief showers when the automatic rain gauge was triggered at 23.07 and later at 00.52 early Tuesday producing just 0.8mm of rainfall, the first measurable rainfall since the 27th, which then only produced 0.1mm. Thus we are half way through April with 0.8mm of precipitation against the 41-year average of 57.6mm.

Tuesday revealed a cloudy start to the new day, however, just before 08.00 the sun broke through gap in the cloud with blue sky appearing. The cloud radar shows a heavy bank of cloud to the east, with heavy rainfall, running northwards and another large area of cloud to the west, also moving northwards, with a small triangular gap between the two, which is likely to be short lived but welcome to start the day. The repositioning of the depression will result in the breeze coming from the east today.

The depression to the southwest is currently over Brittany and will head northwards over the UK as the day progresses throwing more cloud across the country, but variable in its content. The centre of the depression is very close with a barometric pressure reading at Marlborough of 995.8mb at 08.00, the lowest pressure since January. The rain is currently falling over eastern parts of the London area and also over Devon and Cornwall with more to come.

The two cold fronts passed over our area on Sunday as forecast, just before and after midday, that brought thicker cloud and a cooler air stream on the breeze from the west. The maximum of 15.1C was the coolest day since the 9th but still 1.0C above my long-term average. The cloud meant lower solar energy and the UV level back to the ‘Low’ category, not seen since March, likewise we have not seen a westerly since last month. Variable cloud meant the thermometer did not begin to drop away until after 23.20 due to a bank of cloud, but by 04.52 the thermometer had reached its minimum of 1.5C being 2.2C below average.

First light on Monday revealed the low temperature and a much more moist air stream, a humidity of 95% was the highest at 08.00 all month, which had allowed fog to form that at sunrise limited visibility to 300m. However, just before 07.30 the sun began to break through and by 07.50 it had virtually dispersed, just limited to the north of our area and could be seen in the distance over the Thames Valley.

We are now under low pressure systems to the northwest and southwest of the UK. The small low currently over Iberia will migrate northeastwards over France and is forecast to be over southern England this time tomorrow bringing more cloud and the possibility of light rain, there is some disagreement over this feature between the major forecasters. The barometric pressure had dropped to its lowest all month yesterday due to the departure of the anticyclone and arrival of low pressure systems with a reading of 1003.2mb, but eased upwards to day to read 1006.0mb.

The cooler air and reduced sunshine is slowing up the development of the apple blossom but slowly the trees are beginning to change colour.

The maximum of 21.6C on Saturday was exactly the same as on Friday being a significant 7.1C above my long-term average thanks to the many hours of strong sunshine. The increased cloud cover overnight gave us a mild night that saw the thermometer only dip to 6.5C being 2.8C above average. There were a few drops of rain observed very briefly at 19.55 that only dampened the hard surfaces but was not measurable.

Sunday brought us a brief glimpse of weak sunshine after sunrise but cloud very quickly drifted across from the west just after 07.30. This change is due to the anticyclone having deserted us and the depression, centred just off Iceland, throwing a couple of cold fronts across the country today.

The coming week will see the variable weather patten established with, sadly, much less sunshine, the days will not be quite so warm but conversely, the nights will not be so cold.

The first twelve days of April followed the extended dry period in March with no measurable rain having fallen. There is no forecast rainfall in the next couple of days with the possibility of a light shower on Wednesday morning. The sunshine and warm breezes this month has seen the equivalent rainfall of 37.2mm lost through evaporation from ground sources and plant life.