As always the mean pressure chart can reveal a lot about the weather, and in July 2023 it showed why it was so wet and changeable, with near average temperatures across the British Isles. It’s also apparent from it why Iceland was so cold due to the squeeze in the pressure gradient between higher than average pressure across Greenland, and lower than average pressure across NW Europe, resulting in a persistent and strong N or NENENorth East flow of air across the island. It’s not so revealing about the causes of the heatwave across North Africa, which happened in a very slack pressure field in a ridge of high pressure that extended eastward into the Mediterranean from the Azores high.
Well the first thing to say is that low’s are not at all unusual in August. Remember the Fasnet storm of 13 August 1979? Tomorrow’s low has a forecast central pressure of 983 hPahPaA Hectopascal is the SI unit of pressure and identical to the Millibar for midday and is situated close to Birmingham. Below is a graphic of charts drawn using reanalysis data from 1948 so you can make your own minds up. The one that immediately stands out to me is the chart for the 2nd of August 1986, with a GIGIGale Index of 38. Remember this chart uses reanalysis data in a coarse 2.5°x2.5° grid of MSLPMSLPMean sea level pressure is the pressure at sea level, or, when measured at a given elevation on land, the station pressure reduced to sea level assuming an isothermal layer at the station temperature. values so contours may well be lower.
It just so happens that I have this chart, but as you can see the low close to Tiree is already a filling feature, with a minimum central pressure of 988 hPa at 06 UTCUTCCoordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about 1 second of mean solar time (such as UT1) at 0° longitude (at the IERS Reference Meridian as the currently used prime meridian) and is not adjusted for daylight saving time. It is effectively a successor to Greenwich Mean Time (GMT)., and can’t match the forecast depth of tomorrow’s low. So tomorrow’s low looks very unusual, and is likely the deepest low to affect the UKUKThe United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and Northern Ireland. on this date in over 75 years!
