The events of the 16th June persuaded Napoleon to completely alter the focus of his original plan. He now determined to keep the Prussian army on the run while he crushed Wellington and then turn and face Blucher. To this end he dispatched Grouchy with the entire French right wing (33,000 men) on the morning of 17th June. Napoleon himself pursued Wellington but both actions were hampered by violent thunderstorms which restricted all movement to metalled roads and prevented cavalry from outflanking the retreating forces. By the time Grouchy reached the Prussian concentration point at Wavre, all that remained was the rear guard. The rest of the Prussian force had already left to aid Wellington at Waterloo.
He dispatched Grouchy with the entire French right wing on the morning of 17th June
At this time, Napoleon was worried that Wellington would slip out of his grasp under cover of the bad weather. He was anxious to bring the Allies to battle soon because he knew they would never again be this weak. However, he noticed with satisfaction on the evening of 17th June that the British were camped along the Mont Saint Jean ridge and were clearly preparing to offer battle.