Borrasca explosiva (bomba meteorologica) que azoto el oeste de Europa con rachas record de 207 km/h en Pointe du Raz (Bretana).
16 fallecidos en Europa occidental, millones de hogares sin electricidad, danos en bosques y costas atlanticas.
Ciarán is the most extreme storm on this list, and not by a small margin. It formed in an unusually fast jet stream over the North Atlantic and deepened at a rate meteorologists call explosive cyclogenesis: pressure falling more than 24 hectopascals in 24 hours. It crossed the English Channel brushing Brittany and Normandy and then ran down past the Bay of Biscay and Galicia. It was named by the British and Irish group, not by AEMET, which is why it does not appear on the Spanish list of named storms for that season.
The figures that follow are not estimates and have not been copied from any bulletin: they were computed on ERA5, the European Centre’s reanalysis, at a point representative of the area affected — Brittany — and compared with the 29 complete years of the series. What matters is not the number but the rank.
| Variable | During the episode | Rank in the series |
|---|---|---|
| Minimum pressure | 962.1 hPa | is the most extreme in the whole series of the 254,208 hours measured |
| Maximum 10 m wind | 84 km/h | is the most extreme in the whole series of the 254,208 hours |
| Rainfall over 4 days | 60.3 mm | falls in the most extreme 1 % of the series of the 10,589 4-day windows |
| Minimum temperature | 9.0 °C | does not particularly stand out in the series of the 254,208 hours |
At this point, what was exceptional about Ciarán was the depth of the low, the wind and the accumulated rainfall. The other variables stayed within what this place sees with some regularity. To place the rainfall: the wettest 4-day episode recorded at Brittany in the whole series was 85.5 mm, on 4 February 2014.
ERA5 works with cells of about 28 kilometres and smoothed terrain. It describes the air mass well and allows one storm to be compared with another on the same yardstick, which is precisely what cannot be done with station records that have changed site. What it does not see is the detail: a storm that unloads over one particular ravine is averaged across a cell of 800 square kilometres, and that is why its totals are always lower than those of a well-sited rain gauge. For the official figures of an episode, AEMET is the authority.
Data: ERA5 · Copernicus Climate Data Store, CC-BY licence. Sources and methodology →
