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 temperature of 17°C, while the coldest months are January and February, with an average of -5°C. The snowiest months in Eureka are December, February, January and March, with each month seeing an average of 33 cm of snowfall.