Taking the local weather in Lewisville into account is an important factor for planning your visit, especially if you plan to spend your trip by the pool. The hottest months are usually August and July, with an average temperature of 18°C, while the coldest months are February and December, with an average of 4°C. The rainiest months in Lewisville are December, November, January and March, with each month seeing an average of 277 mm of rainfall.