Weather news

Parts of Europe have seen further rounds of severe, even extreme flooding during October. A powerful mid-latitude cyclone containing the remnants of Hurricane Kirk moved east across France on 9/10 October. Slow-moving areas of heavy rain revolved around the depression, affecting the Seine-et-Marne department especially badly, where the Grand Morin River surpassed levels seen during the widespread flooding of 2016. Parts of the National Assembly in Paris were also flooded. Around a week later, parts of southeast France were hit by severe flash flooding as another slow-moving frontal zone with embedded convection brought a couple of days of intense rainfall. As much as 700mm of rain fell in parts of Ardeche and Lozere, leading to widespread disruption to transport and damage to property and infrastructure. This was the worst flooding this part of France has experienced in 40 years. At the end of October, parts of eastern Spain were hit by some truly extreme weather. On the southern side of a diffluent block positioned over northwest Europe, a slow-moving upper vortex, with plumes of warm, moisture laden air spiralling north and west from the western Mediterranean and northwest Africa, destabilised over eastern Spain. This is locally known as ‘gota fria’ or ‘cold drop’ and this phenomenon can often bring severe weather to this part of the Iberian peninsula. Other sources refer to this phenomenon as a 'DANA' – Depresión Aislada en Niveles Altos. The slow-moving severe thunderstorms (Figure 1) brought historic flooding to the region around Valencia, with the town of Chiva recording a year's worth of rain (491mm) of rain in just 8h. Turís, around 10km to the south of Chiva, recorded 772mm in 24h, according to AEMET. Large hail, up to 5cm in diameter, damaged cars and trees in Almeria. At the time of writing, more than 200 people are known to died, with many more missing. (Sources: Météo France, AP News, Euronews, AEMET, ESSL.) The first storm of the 2024/2025 season to be named by the ‘Western Europe’ group of national meteorological centres, Ashley, was christened by Met Éireann and swept through on 20 October. Beginning life as a baroclinic wave with central pressure of 1015hPa, Ashley benefitted from a strong plunge of polar air and associated powerful polar front jet, explosively deepening at a remarkable rate of 50hPa/24h to end up as a 950hPa low well to the west of Ireland. In what was a fairly textbook example of rapid cyclogenesis (although complicated to some degree by a cold air low to its immediate north), a sting jet was inferred from imagery over the Atlantic, but by the time Ashley reached the UK it was a mature feature with a cold conveyor belt and occlusion completely encircling its centre. Gusts in excess of 80mph were recorded on the western Irish coast, 82mph at Aberdaron in west Wales and 81mph was reported at Killowen in Northern Ireland. A gust of 78mph at Tiree Airport was the strongest October gust here since 1972. Orange/Amber warnings were in force from Met Éireann and the UK Met Office. In addition to disruption to road, rail and power from the wind, Ashley also combined with spring tides to bring coastal flooding to parts of western Scotland, including at Fort William where the gauge at Corpach registered its third highest tide on record at 4.05m AOD. (Sources: Met Office, Met Eireann, SEPA, BBC News, SSEN, NIE, Police Scotland.) It has been an active month in the tropics with no fewer than 12 named systems keeping forecasters very busy indeed. While space does not permit a survey of them all, we did want to make special mention of Hurricane Oscar, a tiny and somewhat unexpected hurricane which caught even the specialists by surprise. The usual media culprits made their usual mess of reporting in the run up to the event; earlier model runs had indicated a significant development which some outlets proclaimed would be Hurricane Nadine heading towards Florida. By the time Oscar developed, Nadine had already formed in the Gulf of Honduras to affect Belize. Oscar was so small that its intensity was not fully appreciated until a Hurricane Hunter plane found mean winds just above the surface of almost 100mph, but the radius of hurricane winds extended just 5 nautical miles from its centre. Despite its size, it still packed a punch, sadly causing at least six fatalities in Cuba and damaging over 1000 homes. (Sources: NHC, Colorado State University, Daily Mail, BBC News.) While it has not rained all the time, many parts of the United Kingdom experienced a particularly wet period between October 2023 and September 2024. The biggest departures from average (i.e. greatest positive anomalies) were in some of the climatologically drier parts of the country, for example, parts of central and southern England. Data from UK Centre for Ecology and Hydrology (UKCEH) reveals that river flows across a broad swathe of southern and eastern Britain (and the east of Northern Ireland) were at exceptionally high to record levels on average between October 2023 and September 2024. Indeed, the River Thames at Kingston ran at 202% of average flow on average throughout this period. Only a couple of monitoring sites in western and northern Scotland ran a fraction below normal on average through the same reporting period. The full report can be viewed here: https://nrfa.ceh.ac.uk/sites/default/files/HS_202409.pdf. (Source: UKCEH.) Data from the Copernicus Climate Change Service issued in early November 2024 indicates that it is now virtually certain that 2024 will end up as the warmest year on record in terms of global average surface air temperature, and the first full year to end up more than 1.5 degC above the 1850–1900 pre-industrial baseline. With the year to date running at 0.1 degC warmer than the same period last year, which was the warmest year on record, it would take an unprecedented fall in these anomalies over November and December for 2024 to finish below the 2023 record. October 2024 globally finished 0.80 (1.65) degC above the 1991–2020 (1850–1900) long-term average, and was the second warmest October on record, beaten only by October 2023 at 0.85 (1.70) degC above. (Source: C3S/ECMWF.) A recent study of global forest fire behaviour from Jones et al. published in the journal Science states that carbon emissions from these fires has increased by 60% in the period 2001–2023. The study authors used machine learning techniques to sort global forest ecoregions into a number of ‘pyromes’ which enabled them to isolate and analyse the balance of human, climatic and vegetation factors driving the extent of forest fires. In particular, they found that forest fire emissions have sharply increased in the extratropics over the past 20 years, where the warming climate is a much stronger driver than human intervention, which tends to be a stronger driver in tropical regions. The study also found that fire emissions in tropical regions had actually decreased, due to reduced human activity as well as greater fragmentation of forested areas acting as fire breaks. These trends point towards an increasing challenge to global targets in tackling climate change, with the ability of forests to act as carbon sinks steadily diminishing. The full article can be found here: https://doi.org/10.1126/science.adl5889. (Source: Science.) The world-famous volcano, and Japan's tallest mountain at 3776m high, remained snowless during the entirety of October for the first time since such measurements began in 1894. Following the heat of summer, the reappearance of the snow cap is an annual milestone which on average happens in early October – the previous latest appearance was on 26 October in both 1955 and 2016. Consistent with much of the rest of the world, 2024 has been anomalously warm in Japan, and the summer especially so, being the joint hottest on record. With temperatures through October remaining anomalously warm, and too warm for snow, the snow cap finally reappeared on 6 November, as observed by the Japanese Meteorological Agency (JMA), and confirmed a day later by the local office at Kofu, Yamanashi Prefecture. (Sources: Reuters, BBC News, JMA.) After the devastating flooding wrought by extreme rainfall prior to and during the extratropical transition of Hurricane Helene at the end of September, much of the impacted region has seen little to no rain at all since then. In fact, much of the eastern side of the United States saw no measurable rain throughout October, including a number of major cities such as Philadelphia, New York City, and Atlanta, as the jet stream remained well to the north. These cities, along with nearly 80 other climate sites scattered across the broad region of the eastern United States, recorded their driest month in series going back to the 1860s, whilst a further 50 or so official sites reported their driest October on record. Much of the contiguous United States is now rated as at least abnormally dry, according to the US Drought Monitor. (Sources: NWS, NOAA (climate.gov), US Drought Monitor.) Love them or loathe them, weather apps have become part of daily life for many people. A recent informal study conducted by the University of Reading's Department of Meteorology has aimed to highlight the strengths and weaknesses of some of those most commonly used in the United Kingdom. The research compared the apps' forecasts to actual weather over 2 weeks in Reading and 1 week in Narberth, South Wales, so from the outset it should be noted that this study was conducted over a limited time period in just two locations within the same climatic zone. AccuWeather came out on top for the accuracy of short-term forecasts (nowcasts), while the Met Office fared best for forecasts a few hours into the future and The Weather Channel was deemed best for forecasts for the following day. Though as a probable user of a weather app, or perhaps several of them, you may have your own opinion! Weather apps notwithstanding, the undoubted value of national meteorological institutions the world over is exemplified by a recent independent economic study which concluded that the Met Office will deliver £56 billion to the UK economy over the next 10 years. This is equivalent to a return of almost £19 per £1 spent. The full report can be viewed here: https://www.metoffice.gov.uk/about-us/news-and-media/media-centre/corporate-news/2024/met-office-delivers-gbp56-billion-of-economic-value-to-the-uk. (Sources: Inews, Met Office.)