Planning for the weather is an important factor for making your trip to Lao Cai a success, especially when you're splurging. The hottest months are usually May and June with an average temp of 80°F, while the coldest months are January and December with an average of 61°F. The rainiest months in Lao Cai are August, July, June, and May, with each month seeing an average of 12 inches of rainfall.