The first thing Shire decided to do in his counterattack was to regain control of the air.
He didn't want his troops to be discovered by the enemy, nor did he want the direction and even the route of the march to be constantly under enemy surveillance.
More importantly, he didn't want his troops to be strafed or bombed by enemy aircraft.
On rainy days, the direct casualties caused by enemy bombing and strafing aren't significant, but it affects the speed and morale of the troops.
Once the air superiority is regained, all these troubles will be eliminated.
These issues will turn into the Germans' troubles: Shire's fighter planes will constantly harass the German Army's 17th Army Group rushing to reinforce, making their advance on muddy roads extremely difficult.
Moreover, once the "Curlew" fighters appear, even bombing the rear transportation lines will be impossible for the Germans. If their bombers are discovered, there's no return for them.
