Strategic Surprise:
The ultimate NATO nightmare. Peacetime circumstances, but somewhere in the depths of the Kremlin, the military overwhelms the Party and KGB, forcing them to launch a conventional strategic strike against the NATO powers (most unlikely). All Soviet forces launch within 48 hours, and catch the NATO air forces on the ground, the border forces are left to their own devices, and naval forces are caught by sneak sub-launched strikes (where possible). Heavy damage is done to NATO's Reforger sites, and to West Germany's lines of communications. Supply being the key. Soviet forces will be strangling for supplies, especially fuel, within 7-8 days, so its a question of how far can they get with what they have against scattered resistance.
Now, the Warsaw Pact is mobilizing fully and undamaged, while NATO forces are reeling. IOTL, the Soviets, against NO resistance, overwhelmed Czechoslovakia in 1968 using a conventional military force in far better shape than in the 1980s. Yet still, within hours of the complete occupation of the country, every Soviet tank in the country was immobilized by empty fuel tanks. These are the things you risk using strategic surprise. To lull the enemy (or AN enemy), you have to give them reasons to be lulled. Which means, hold off any real signs of mobilization until it becomes absolutely necessary. Not unlike Arab strategy in 1967 compared to 1973.
IMO, this scenario is the least likely, but if it happens, will result in Soviet air superiority for the time of the campaign (one to two weeks), but also the one most likely to see the opening use of tactical nukes by NATO, leading to a full WWIII. If its still conventional no matter what, then IMO the Soviets close up to the Rhine, while lacking the logistical mojo to get any further. Even Denmark and the Low Countries, despite their vulnerability, are unlikely to be taken. Yugoslavia and Austria will have to be left alone, as their neutrality protects the Soviets' southern flank. This is also the scenario that gives the best chance for doing major damage to the heaviest NATO forces, the American, in the center, while the main northern thrust goes forward.
However, Soviet war plans in the 1980s were largely unchanged from the 1950s, when the north of West Germany was still largely flat wide open farmland, ideal for Soviet armored warfare. In the 1980s, this region had become much more developed, making the usual grand tank army sweeps planned by the Soviets more problematical. OTOH, this region was defended by the Dutch and Belgians, who would not be deployed in their wartime stations in this scenario.
Better for the Soviets, even US readiness was horrible at the start of the decade. Though I believe the figure was during the Carter Administration, one US airbase had 72 F-15s stationed there, with 70 of them down for spare parts.
So, conventional only, the more surprise the Soviets get, the earlier in the decade, the better they do. No WMDs, and they're likely to secure much of West Germany, but little beyond that. A longer war following this is anybody's guess. It depends much on a complete X factor: Political cohesiveness in what remains of Western Europe. (to be continued)
I know this is supposed to be about air power only, but NATO v. Warsaw Pact isn't the Battle of Britain.