Planning for the weather is a good way to make your trip to Eureka relaxing and enjoyable, especially when you’re splurging. The hottest months are usually July and August with an average temp of 62°F, while the coldest months are January and February with an average of 23°F. The snowiest months in Eureka are December, February, January, and March, with each month seeing an average of 13 inches of snowfall.