Our study focuses on the impact of weather on the returns of the Casablanca Stock Exchange, using the GJR GARCH model and over a period between 02/01/2012 and 29/01/2021, we tested the impact of temperature and precipitation on the performance of the MASI. The results of the estimation of this model confirmed the impact of the weather on investor mood and then on price formation in the Moroccan case, and that high temperature have a negative impact on MASI's performance. So, we should introduce behavioral variables to explain financial phenomenon which traditional finance has not been able to do.