From North Atlantic Cooling to Omega Blocking: Dynamical Pathways to the June 2026 Western European Heatwave

Atmospheric blocking is a major feature of mid-latitude circulation and is closely associ-ated with the occurrence of extreme weather events over Europe. Among the different blocking regimes, Omega blocks are characterized by their persistent tripolar structure, which favors the development of prolonged heatwaves. In late June 2026, Western Eu-rope experienced one of the earliest and most intense heatwaves of recent decades. This study investigates the synoptic, dynamical, and climatic mechanisms associated with this event using ERA5 reanalysis data. The evolution of the 500 hPa geopotential height, 850 hPa temperature, polar jet stream, Rossby wave breaking, and dynamical tropopause (2 PVU) was analyzed together with anomalies in sea surface temperature (SST), meridional temperature gradient, soil moisture, and sensible heat flux. The results show that the heatwave developed under a persistent Omega blocking pattern, which promoted strong subsidence, enhanced solar heating, and sustained warm air advection over Western Europe. The event was further amplified by land–atmosphere feedbacks associated with anomalously dry soils. In addition, a pronounced cold SST anomaly over the subpolar North Atlantic preceded the onset of the blocking and coincided with a weakened me-ridional temperature gradient and reduced lower-tropospheric baroclinicity along the climatological position of the polar jet stream. These findings are consistent with recent studies suggesting that North Atlantic cooling associated with a weakened Atlantic Me-ridional Overturning Circulation (AMOC) may create favorable conditions for persistent summer Omega blocking and associated European heatwaves.