Case studynew
Why the UK forecast flipped: 19–26 October 2026
Up to 14 October the ECMWF ensemble forecast a dry, high-pressure week for the UK; over the next three runs it flipped to low pressure and rain, and the flip proved right. This storyboard works backwards from the UK through a North Atlantic block that never happened, a Rossby wave packet and a trough that split over North America, to a short wave that came ashore in British Columbia and phased with an upper low over the Four Corners.
- ECMWF IFS & AIFS ensembles
- Forecast verification
- Rossby wave packets
- Radiosonde observations
- Typhoon Koguma