From: Lower Saxony Germany
If I remember correctly aircraft can't fly when their airfield hex is in mud.
Airfields are viewed as grass field where fighter planes flew, mud and snow make it impossible to fly.
I your opponent is not in a mud hex he can still fly and you can only relay on Flak to defend your skies.
A bit of a pain, but if you keep an eye on the weather, you can react in time.
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