After the deluge at the end of March the rain eventually stopped just after 10.00 on Saturday as the wind veered from the west into the north, this was due to Storm Mathis moving away and a ridge of high pressure just beginning to assert itself. The maximum of 11.2C for the beginning of April was 2.9C below the average due to the cloud and cooler northerly airstream. However, that same cloud cover meant a minimum of 6.4C was 2.7C above the average.
Sunday first thing revealed the cloud still in place with light drizzle at 07.00. The wind continued from the north and quite brisk that for the first time in three weeks meant that there was a wind chill so that outside although the thermometer 6.5C at 08.00 it felt more like 5C.
The ridge of high pressure, reaching from Norway to Portugal, has intensified that saw the barometric pressure rise 22mb since Saturday with a reading of 1025.0mb at 08.00. This will mean a drier period, hopefully with sunshine later in the day
March 2023 Review
From the very beginning of March, the weather reverted back to Winter with a persistent north-easterly then northerly airstream. Maximum temperatures were below average until the 10th. The coldest night of the month occurred in the early hours of the 11th when the thermometer dropped to -3.2C, which was 5.6C below the 39-year average.
During this period significant snowfall occurred on three days, 7th, 9th and 10th. The initial fall on the 7th revealed 8cm depth of level snow, which was added to on the 8th before it turned to rain and a thaw set in. The wettest day on the 9th produced 13.2mm of precipitation.
Storm Larissa, named by Météo France as they were on the southern flank and were hit hardest, was the cause of the later snowfall. However, thankfully for us the worst of the storm was felt in the north if the UK.
The 8th was a particularly cold day when the thermometer did not rise above 1.2C, which was 9.4C below the average and the coldest day since 23rd January.
The next two days brought very disturbed weather with the south-westerly wind gusting 37mph and 48mph on the 12th and 13th respectively.
It began to feel more like Spring from the 16th as maximum temperatures began to be consistently above the average with a high of 15.2C on the 21st being +4.6C. This was the warmest day since 13th November.
The wet and very windy five-day period from the 20th not only produced significant daily rainfall totals but was also very windy. This was due to a depression lurking just to the west of Ireland that produced the strong south-westerly winds gusting to 29mph at its peak.
The rainfall on the 21st took the monthly total above the 39-year average for the first time in March.
The depression slowly moved across the country so that on the 25th it began to merge with another low pressure system over Scandinavia as a result the wind began to veer into the west and then from a northerly quadrant on the 26th that saw the temperatures drop significantly under the short lived Arctic air stream.
The end of the month was dominated by a mild, moist south-westerly air stream. The rainfall was added to significantly by the arrival of Storm Mathis, named by Météo France, a deep and large depression. The wettest day for two months, 30th/31st, added another 16.8mm, that took the monthly total to 134.6mm and broke the record for the wettest March set by March 2018 (130.9mm). At 08.00 on the 31st the March rainfall was 229% of the long-term average.
The last day of March was appalling as it rained all day until 22.00 and then began again in the early hours of the 1st. The rainfall during that twenty-four hour period was 28.7mm making it the wettest day since 19th December.
The March rainfall amounted to 163.3mm, which was 277% of the 39-year average or plus 104.5mm and well and truly smashed the record set in 2018 (130.9mm). Even though we had a dry February the rainfall for the period January to March was 60mm above the long-term average.
There were 22 days in March described as wet days by the Meteorological Office, that is rainfall equal to or above 1mm, when the average is 11.
Air frost occurred on only 5 days as against the average of 8 days, so it was not surprising to find that the mean temperature for March was 0.5C above the 39-year average.
It was the dullest March since my solar sensor was installed in 2010 being just 81% of the 13-year average.
Atmospheric Rivers
Atmospheric rivers are relatively long, narrow regions in the atmosphere – like rivers in the sky – that transport most of the water vapour outside of the tropics. These columns of vapour move with the weather, carrying an amount of water vapour roughly equivalent to the average flow of water at the mouth of the Mississippi River. When the atmospheric rivers make landfall, they often release this water vapor in the form of rain or snow.
California has recently been experiencing this phenomenon with 12 occasions during March that produced major flooding and significant property damage.
The atmospheric rivers are greater than 2,000km long and less than 1,000km wide and have at least 2cm of vertically significant precipitable water. They collect moisture from the tropics and carry it northwards.