The positive North Atlantic oscillation with downstream blocking and Middle East snowstorms: The large-scale environment

The NE-SW [northwest-southeast (NW-SE)]-tilted EB dipole occurs with a southward (northward)-displaced NAO⁺ event. The NE-SW-tilted EB dipole anomaly is associated with an arching-type low-frequency wave train that spans the North Atlantic, Europe, and the Middle East. This tilting has the most favorable structure for cold air outbreaks over the Middle East and southeastern Europe because this tilting leads to an intense downstream trough over this region.

In contrast, a NW-SE-tilted EB dipole anomaly leads to cold temperatures over northwestern Africa and southwestern Europe. The analyses herein also suggest that a strong jet over the North Atlantic may be a precursor for a southward-displaced NAO⁺ event that is usually associated with an Ω-type EB with a NE-SW-tilted dipole in the anomaly height field that favors a cold air outbreak over the Middle East.