Quantifying the effect of weather on sales

Note to the reader: This article assumes some familiarity with data science and analytics concepts. The finance team of a major Australian retailer wanted to know the answer to the question of "How much does the weather affects the weekly sales?" However, nobody in the business has a scientific method of solving it. As pointed above the business value of solving this problem is tremendous, as this could help better understand the impact of certain weather events on the top and bottom line. Not just that, the business can better monitor and report weekly transactional habits of the customer, which are influenced by the weather.