Final answer:
During the Wars of the Roses, heavy rain impeded the Lancastrian archers and assisted the Yorkist ones by reducing the effectiveness of the Lancastrian's longbows, which helped the Yorkists win the Battle of Towton.
Step-by-step explanation:
The weather condition that impeded the Lancastrian archers and assisted the Yorkist ones was heavy rain. This event occurred during the English Civil War known as the Wars of the Roses. The Yorkists benefited from this weather condition because the rain dampened the Lancastrian's longbow strings which reduced the effectiveness of their range and impact while the Yorkist archers protected their longbows and thus maintained their ability to fire effectively. This was a crucial factor in the Yorkist victory at the battle of Towton, a significant event within the Wars of the Roses.
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