MOSCOW (AP) — Thick clouds have forced the cancellation of the traditional dramatic conclusion to Russia’s annual Victory Day parade on Red Square — the roaring flyover by scores of military aircraft.

The parade marking the anniversary of Nazi Germany’s surrender is a highly ritualized display and marked changes in its order are unusual.

The Defense Ministry had said cloud-seeding planes would be deployed to disperse the overcast skies Tuesday above Moscow. That has been done previously when poor weather threatened. It wasn’t immediately clear if the planes had been deployed.

Victory Day is Russia’s most important secular holiday, commemorating the Red Army’s determination and losses in World War II.

President Vladimir Putin said in his parade address that “we feel a piercing blood relationship with a generation of heroes and winners.”